How to make jpeg format on iPhone

Table of Contents

Graphics editor

The most famous and easily accessible way for these purposes is to use any graphics editor. In this example, we will consider Paint, since this program is in every Windows, which means that everyone can use it.

Open Paint in any way convenient for you. I personally prefer to open it with the “Run” line. In general, I really love this line. In general, open it (for those who do not know, press the WINR key combination). Well, in the line itself, write mspaint and click OK.

In the editor, click on the “File” menu (the button that is responsible for the main menu items). And already from the drop-down menu, click “Open”. Now find on your computer the image you need and it will open in the editor.

make, jpeg, format, iphone

I decided to open the image in PNG format. In principle, you can open the most common formats in Paint, such as PNG, JPG, BMP, GIF. Well, in general, now all we need to do is to click on the “file” menu again, only this time select the “Save as” item. “. If you haven’t noticed, an additional menu has appeared a little to the right with possible image formats.

I came here to make JPG from PNG, so I select “Save image as JPG” and look for a place to save. That’s all. We didn’t even have time to sweat).

We change the image format to jpg or any other in three different ways

Good day to you, my dear friends. How is your mood? I seem to have nothing. Although it has been better. But today is not about that. I remembered here one case, how one employee came with the fact that her picture was not uploaded to some site. She says that she did everything as said, and when she wants to select a file, it seems as if it is not in this folder. She was there, almost in convulsions, looked for this picture, made several copies, deleted everything except this file in the folder. It turned out to be simple. This downloader required uploading files only in the graphic format JPEG (JPG) and in no other.

Usually, most pictures and photos are in this format, but this is not always the case. Well, then I explained to her how to change the image format to jpg so that everything would meet the requirements.

In general, the procedure is simple. Quite the opposite, even a very simple one. Therefore, I will show you today 3 different options, with which you can convert an image to jpeg or any other format.

Crunch your fingers. Come on, come on! Fingers need to knead. Now let’s go!


The next method is also simple, although it requires the installation of an additional converter program. But it is done once and for a long life. If you don’t know, a converter is a program that converts one format into another. And it doesn’t have to be a graphic format. Converters are also created to work with audio and video formats, well, with others. I will not go deeper. About this in a separate article.

Let’s download the Format Factory program. This is a special universal converter that works with different types of files. You can download it from here. Do not worry. This is a proven site and will not take money from you.

Download, install and run. Here’s a simple procedure. But this, of course, is not all.

  • So you are in the program. Now you need to choose the type of files from which you will convert. We need images, so choose “Photo”.
  • In a new window that opens, you see the available image formats. What format do we need? In principle, any, but in this example we are considering just JPG, so click on the icon with the inscription JPG.
  • Next, another window will open for you. Here we need to upload the files that you want to convert (difficult word? Don’t get used to it). To do this, click on the “ADD” button, and in a new window that opens, select one or more files that you want to convert to JPG. As you can see, I have selected 2 PNG files. Now click OK. And if you wish, you can delve into the settings, but I will not dwell on them.
  • Well, now we see that our 2 files are already in the project. Now you can convert, but first look down. Opposite the inscription “Destination folder” is written the destination where our files will come. You can change this path by clicking on the corresponding “Change” button. Click and search for the desired folder. Well, at the end, we press the coveted OK button.
  • Did you think everything? It was not so. Now we will be thrown back to the main window of the program. only now, note that our files have appeared on the right side, their size and what they will be named after conversion (and of course in what format they will be). As you can see, the name remains the same, only the format is different. True, this is only a preview. In fact, these files have not been translated yet. It remains for us to do the final touch, namely to press the “Start” button.
  • After a short time, depending on the size of the files (it took me 1 second), you will see that everything is done (it will be written this way), and at the same time you will hear a sound signal. We’re done, but to be sure we’ll go to the final folder. Everything is in place. Everything is converted and opened. So our task is completed.

But that’s not all. Take a short break and we will find out another quick way.

Online converter

There is another rather easy way that does not waste your time and effort. Now we will again use the converter, only via the Internet. What is the advantage of this procedure? What do you think? Of course, you don’t need to install anything, since you will be working with the site. Let’s go to one such site, for example. As you can see, this converter is also versatile and can translate not only image formats, but much more. It’s just that in this case we will do everything using the example of transferring from PNG to JPG.

  • Select the item “Convert” to JPG in the “Image Converter” section.
  • Now select the file on your hard drive that you want to convert to JPG. If you do not have a file, but there is a picture on the Internet, then you just copy the address of this link and paste it into the appropriate line. Besides that, you can play around with other settings. As you can see, everything is clearly written here. I usually do not change anything, well, I only set the best quality and change the resolution in rare cases. In general, if you need to change something in the image, then I’d rather use the same Photoshop. By the way, in Photoshop, you can also save in a different format, but I will not consider this here.
  • Well, in the end, as you yourself probably already guessed, you just need to click “Convert file”. That’s all.
  • After the conversion is completed (from one to several seconds), your new converted file will start downloading to the folder where you have all the default downloads. Just open the file and enjoy.

Well? Which of the presented methods is the most convenient for you? Or maybe you have some interesting way of your own. Then write in the comments. Do not be shy.

Files can be converted to any format. But what will happen if a failure, a powerful virus, technical damage, human misconduct and other factors destroy files that are so important to you. In this case, you shouldn’t really count on antivirus. To be ready for all this, I recommend that you watch a powerful and interesting video course on file protection. Everything is told in human language and is designed for any level of knowledge. In general, if your important data is dear to you, then it is better to play it safe.

Well, this is where I end my article today. I really hope that you liked my article, so do not forget to subscribe to my blog updates, then you will definitely not miss anything interesting. Well, I say goodbye to you. See you soon. Bye Bye!

How to change the photo format to JPEG

1) Open Settings.

2) Select the Camera section.

3) Go to the Formats item.

Note: If your device does not support HEIF / H.265 formats, you will not have this item.

4) Select Most Compatible.

After that, photos and videos will be saved in the old JPEG / H.264 formats.

After changing the settings, existing photos and videos in HEIF / H.265 formats are not converted to JPEG / H.264.

Tip: If you have HEIF images in Photos and would like to transfer them to your computer as JPEGs, go to Settings → Photos and select Automatic at the bottom of the screen.

This converts files to JPEG / H.264 when transferring over USB.

IPhone 8 and iPhone X owners will have to change settings every time they use shooting modes that require HEIF / H.265.

iOS automatically changes JPEG / H.264 to HEIF / H.265 when shooting Slow-mo at 1080pHD at 240fps or 4K video at 60fps.

How to take jpeg snapshots with iOS 11

If you have an iPhone 7 / model newer or iPad Pro 2017, then you may have noticed that after installing the iOS 11 update, pictures are saved in the new format. HEIC, and videos. in HEVC or H.265, instead of the usual JPEG and H. 264.

The new format is great, it retains the same high quality, and at the same time the files take up much less memory. HEIF images take up almost half the storage space, sync faster via iCloud and consume less bandwidth while transferring.

HEIF as the new standard

The Camera app on an iOS 11 device saves HEIF / H.265 files by default if the device supports them.

HEIF / H.265 is supported on devices with A10 Fusion processor and newer. These include the following models:

  • iPhone 7
  • iPhone 7 Plus
  • iPhone 8
  • iPhone 8 Plus
  • iPhone X
  • 5-inch iPad Pro
  • 9-inch iPad Pro (2nd generation)

If your device is listed above, and you have already installed iOS 11, then you may want to revert to the usual JPEG / H.264 formats.

HEIF compatibility

With this, problems will not arise so long.

Ultimately, HEIF images will completely replace JPEG, not only because they take up half the memory, but also because they have many more advantages. So far, the format is not supported by all applications and devices, so it is worth switching to JPEG / H.264.

Switching from new formats is optional as iOS 11 can automatically convert them to JPEG when streaming via various apps or AirDrop.

In addition, HEIF files are converted to JPEG when you open them in applications that do not support this format. In other words, you can continue to shoot in the new economical formats and not worry about their compatibility, since iOS 11 has already taken care of this.

What is the photo format on iPhone?

With the iPhone 7, Apple smartphones capture HEIF photos. The new extension reduced the size of the files while maintaining the original quality. The disadvantage of the iPhone photo format is the inability to view the image on previous iPhone models or on computers with a different OS. When uploading pictures to social networks, the photo automatically changes the format to compatible with the service program.

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How to change HEIF photo format to jpg in iPhone

JPG is a photo and picture format known to all users of digital devices and computers. JPG has long foreshadowed imminent extinction, but the expansion is still popular and in demand today. Apple is famous for its desire to make all the tools for its devices on its own, but the photo format on the iPhone is not like everyone else.

If you exclusively use Apple products, there are no problems. Other platforms, however, do not recognize the HEIF or HEIC extension. Therefore, the question arises, how to change the photo format to jpg in iPhone.

How to disable HEIF and change to JPEG?

Do not get upset right away, Apple has provided all the options and offers to change the camera shooting settings.

Instructions on how to change the HEIC format on an iPhone.

  • Enter the “Settings” menu.
  • Select “Cameras”.
  • Item “Formats”.
  • By default, the checkbox is set to “High Efficiency”, move it to “Most Compatible”.

Now the smartphone shoots video in the usual JPEG. However, be prepared for the fact that files with this resolution take up 30-40% more space than HEIF. Here you have to make a choice between the efficiency of using the device and the ability to share a photo.

Another way how to change HEIF to JPEG iPhone is to use online format conversion services. They are free and available without registration. Stages of work:

  • In the search bar, fill in the query “photo converters from HEIF to JPEG. Will choose the appropriate.
  • On the site page there will be a place to download files from your computer. Upload a photo.
  • Start converting.

After the end of the process, the file in the converted extension will be downloaded to the device. There are programs with similar functions. For example, iMazing. Usage instruction:

  • Find and download the program on the Internet. She’s free.
  • Wait for the download, follow the prompts in the dialog box that appears.
  • Select HEIF images by right clicking.
  • Bring to the iMazing main window.
  • At the bottom of the page, in the “Format” tab, select JPEG.
  • In the Keep EXIF ​​data item, check the box.
  • In the tab, the quality will select the desired result. Remember that the higher the quality, the “heavier” the file. Recommended amount. 85%.
  • Choose the folder where to save the photo.
  • Start converting.

The conversion time depends on the number of objects and the capabilities of the PC, but usually the process takes several minutes or seconds. If you don’t want to constantly think about how to change the HEIF format to JPEG iPhone, use tools that automatically change the extension when transferred to another device. To do this, use “share”. The method works for iOS 11 and macOS High Sierra.

To enable the option go to “Settings” → “Photos” → select “Automatically” transfer to Mac or PC with Windows, Symbian or Linux. After that, HEIF files will be transferred already in JPEG. In this case, no additional conversion is required. The quality of the images does not change, but with frequent “flips” from one expansion to another, the image may deteriorate.

How to convert to jeepg or other graphic format?

There are many different ways to change the aspect ratio of a photo. The file format determines in which program it can be opened or edited. The file extension defines this format. Most people working with images will have to convert these files to a different format at some point, so it’s worth exploring a few different ways to accomplish this. JPEG (aka JPG) is the most commonly used image format.

How can I change the photo format to jpg or another? Converting images on mobile devices

How can I convert.avi to.jpeg?

.avi is a video format and jpeg is an image format. First you need to take a snapshot of the video frame during playback and then save the image in jpeg format.

How can I convert an image to jpg or other graphic format? Changing the file extension manually

  • Make the file extension visible. Depending on the specific settings, the file extensions (three letters after the period in the file name) may not be visible for the standard way of viewing files. For Windows operating systems, you can configure the appropriate options on the View tab under Folder Options. It’s in the “Appearance and Personalization Options” section. On a Mac, these options are set in the Advanced Search Preferences section:
  • Rename the file. Right-click on the image file and select Rename. Remove the old extension and add a new one.

For example, if the file name is “myimage.png”, you can rename it to “myimage.jpg”, and from now on your computer will see it as a file in the “.jpg” format.



  • The.jpg and.jpeg extensions mean the same and can be used interchangeably on modern operating systems. This distinction stemmed from early standards for some systems, in which only a three-letter extension was allowed;
  • File extensions are not case sensitive, although it is generally accepted convention to use lowercase.

Questions and answers

How to convert images from PNG to JPEG?

How do I change the aspect ratio on my computer? Paint or MS Paint is a simple image viewing and editing program included with the Windows operating system. Open the PNG file in Paint. and then use File Save As to save the file in JPG format. If you are on a Mac. you can use iPhoto. Open the PNG file in iPhoto. then go to File Export and select JPG from the list.

How to save photos in older, more compatible formats?

If you’re having problems with HEIF (.heic) files or HEVC videos, you can easily change your iPhone or iPad’s settings to keep the old way. Photos will be saved in.jpg format, while videos will still have extension but use more versatile codecs.

To restore the saving of images in JPG and movies in the old standard MOV, go to “Camera Settings” and then select the “Formats” tab.

Here you can switch between the old and new way of saving photos and videos. The default is “Most Efficient”. which means new formats HEIF and HEVC are used.

If you want to revert to older formats, select the Most Compatible option. From now on, photos will be saved in JPG format and MOV movies with support for old codecs.

How to disable HEIC photo format on iPhone and get JPEG back

For a long time I have been using my iPhone X as a camera, taking most of the photos for my materials on

Every time it comes to processing photos taken in Photoshop on a MacBook, I experience incredible pain: all photos transferred via AirDrop are in HEIC resolution, which is not perceived by Photoshop.

You need to open each photo using standard macOS tools, convert to JPEG and save. It takes time and is generally inconvenient.

But you can fix everything in just one click.

thank re: Store for helpful information.

How to set up saving photos to iPhone in JPEG

4 tapas. and JPEG is back.

To return the JPEG extension for all photos taken in the iPhone gallery, you need to do the following:

Go along the path “Settings”. “Camera”

Open the item “Formats”

Select “Most Compatible”

After that, everything will be fine: the photos will be saved in JPEG, you can transfer them to a PC or Mac, edit in Photoshop and not waste time converting from one format to another.

Please note that choosing the “Most Compatible” item, you will not be able to shoot videos in 4K / 60 frames. sec and 1080p / 240 frames. sec. To shoot with such settings, you need to return the tick to “High efficiency”.

If you choose the “Most Compatible” setting, then make sure you have memory on your smartphone: pictures in JPEG take up more space than in HEIC format. Although, I have 64 GB of memory, and I do not feel any inconvenience.

(3.41 out of 5, rated: 54)

How to Save Photos to JPG instead of HEIC on iPhone (iOS 11)

Photos taken by iPhone from iOS 11 are saved by default with HEIF extension instead of JPG. However, there is a way to restore JPG format as default extension for photos.

In iOS 11, quite a few changes were made to the recording of photos and videos created by the built-in camera. After the update, all new photos and videos are saved using completely different formats. HEIF (extension.heic) and HEVC (

HEIF is the standard for photographs that replaced the JPG format on the iPhone. Photos created in this standard have the.heic extension. This means that all new images captured with the camera in iOS 11. are saved with the.heic extension. not in.jpg.

HEVC. in turn, is the standard for movies recorded using the camera. It is based on the H.265 codec and is the default format for saving videos. Here, however, the changes are smaller, the same, the recorded file extension remains the same as before, However, these videos may not play on older devices that do not support H.265.

How to take jpeg snapshots with iOS 11

If you have an iPhone 7 / model newer or iPad Pro 2017, you may have noticed that after installing the iOS 11 update, pictures are saved in the new format. HEIC, and videos. in HEVC or H.265, instead of the usual JPEG and H. 264.

The new format is great, it retains the same high quality, and at the same time the files take up much less memory. HEIF images take up almost half the storage space, sync faster via iCloud and consume less bandwidth while transferring.

HEIF as the new default photo format

As mentioned, the camera app in iOS 11 defaults to HEIF for taking photos if the device supports it.

The following devices can capture HEIF photos and record H.265 video:

  • iPhone 7
  • iPhone 7 Plus
  • iPhone 8
  • iPhone 8 Plus
  • iPhone X
  • 10.5-inch iPad Pro
  • 12.9-inch iPad Pro (2nd generation)

How to take a JPEG photo after updating to iOS 11

Owners of devices ranging from iPhone 7 and up, as well as iPad Pro, may have noticed that after updating to iOS 11, the camera app uses a new format by default for capturing photos and videos.

In iOS 11, Apple included HEIF and HEVC by default for capturing photos and videos on new devices. This will save up to half of the storage capacity, but does not guarantee the compatibility of the received photos and videos with third-party devices and services.

How to make a scan on iPhone IOS 13?

How the built-in scanner works on iPhone and iPad

  • Click Browse at the bottom of the Files app.
  • Click the button (three-dot icon) at the top of the menu.
  • Select “Scan Documents”.
  • Place the document within the screen and press the button to take a snapshot.

How to scan documents from printer to computer?

How to scan from printer to computer

  • open the “Start” menu;
  • go to the “Control Panel”;
  • go to the tab “Hardware, Sound” / or “Devices and Printers” for Windows 7 and then “Printers”;
  • select the line “Start scanning”.

How to scan a file on iPhone?

  • Launch the standard Notes application.
  • Create a new note and click the “”.
  • Select Scan Documents.
  • Point the camera at the desired document, the system itself will try to recognize the boundaries, take a photo.

How to make a PDF file on an iPhone?

To create PDF on iPhone, you need to open a compatible format in an application that supports PDF editing. In our case, this is Adobe Acrobat Reader. Next, in the menu, you need to select the Create PDF item, it can be called Export PDF in other applications.

How to sign a document on iPhone?

How to sign a document on iPhone or iPad

  • Go to the “Mail” section and open the email with the attached document.
  • Click on an app to open it.
  • Click the pen icon in the upper right corner of the document.
  • Next, click the icon in the lower right corner.
  • This will open a blank page.
  • You will now see your signature displayed on top of the document.

How to make a PDF file from a photo?

How to Convert JPEG Image to PDF Format

  • Download and install Universal Document Converter.
  • Open a JPEG image with Windows Picture and Fax Viewer and click the Print button on the toolbar.
  • In the Photo Printing Wizard window, click the Next button.

Where is the QR code of WhatsApp on iPhone?

iPhone. Open WhatsApp Settings. Click the QR code icon next to your name.

Other functions of the application

  • Sorted by name: A-Z, Z-A, by file creation time.
  • Change the order of saving (long press on the image and then drag to a new location)
  • To delete one image (swipe to the right) or all images (in the “Clear List” menu).
  • Color (as is, grayscale, black and white).
  • Setting the maximum image size (proportions are maintained).
  • Set password
  • Renaming the file after generation (by default, a file is created with the current date and time).
  • Make a choice of the image format saved to PDF, for example, so that all files are saved in JPG format with a specified compression ratio, then the output will be a PDF file, in which you can say a full-fledged JPG to PDF converter is used, or let’s say you know that your images are will look better if you use PNG format, then you just select it from the list and get a PNG to PDF converter.
  • The next step is to specify the page format and fit the image exactly to the page size, in this case it will be ideal for printing.
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JPG is a photo and picture format known to all users of digital devices and computers. JPG has long foreshadowed imminent extinction, but the expansion is still popular and in demand today. Apple is famous for its desire to make all the tools for its devices on its own, but the photo format on the iPhone is not like everyone else.

If you exclusively use Apple products, there are no problems. Other platforms, however, do not recognize the HEIF or HEIC extension. Therefore, the question arises, how to change the photo format to jpg in iPhone.

How to make jpg format on your phone

Nowadays, the JPG format is widespread, popular and easy to use. Files in this format are lightweight, can be easily opened in any program for viewing and editing images and sent by e-mail without any problems.

On the other hand, JPG is not recommended for compressing drawings, text and sign graphics. Since after compression there are noticeable digital artifacts. It is better to save such images in formats such as PNG, GIF, TIFF. With Photo Converter you can always quickly and free of charge convert any graphic formats to JPG.

Online conversion

Some of the features of Photo Converter can be tried online. Select files or ZIP archives to convert:

Here are some tips for a successful conversion:

Select files to convert. If you have a whole list of images that you want to save as jpg, use batch conversion. With it, you can convert 100 or even 1000 photos at once.

How to convert RAW Photo into JPEG/JPG in any iPhone Devices ?

Select the editing tools. With this option you can (crop, rotate your image, adjust brightness, contrast and much more).

Select the format for conversion, in our case it is JPG.

It remains to press the Start button and in a few seconds you will receive your files converted to JPG format.

Command line interface

Professional users can use the command line to convert and edit in manual or automatic mode. For additional advice on using the cmd interface, contact User Support.

Imagine that you decided to write an application for converting from JPG, BMP, WEBP and PNG to PDF, in your opinion, useful for users, and wrote it.

Nice feature and sometimes useful, why? For example, banks sometimes ask for PDF instead of pictures, and try to collect 5 pieces of images, for example, JPG in PDF, this is the goal they set themselves.

Next, you still make an application, and the question arises about its promotion on Google Play.

Search and find. It turns out that there are analogues of your application, and there are 120 of them. Try typing the request “Image to PDF” in Google Play and see for yourself. 95% of applications have the same design, the only difference is in colors, icons and whoever released it. It looks like a whole village of Indians had a task to release an application and upload it to Google Play and get 100 installs in a year, tk. no one in their right mind would post an app or try to promote it. By the way, it’s a good idea to publish an application template and sell templates. you will earn much more.

What is the photo format on iPhone?

With the iPhone 7, Apple smartphones capture HEIF photos. The new extension reduced the size of the files while maintaining the original quality. The disadvantage of the iPhone photo format is the inability to view the image on previous iPhone models or on computers with a different OS. When uploading pictures to social networks, the photo automatically changes the format to compatible with the service program.

How to convert from JPG to PDF

When converting from JPG to PDF or from PNG to PDF, you only need to follow a few steps:

  • Add images, JPG, PNG, WEBP and BMP formats are supported. These are the native formats for Android. We support native formats to avoid making this converter online. If you have images that do not open in Android. we can use our online image converter.
  • Click on the “Create” button at the bottom of the screen:
  • Set the settings you need (maximum image size, password, color) and click on “Convert to PDF”
  • Wait for the result and take the necessary actions further (you can rename your file, send it to someone or open it to evaluate the result).

We understand that now the number of functions is minimal, but if the application is in demand, we will definitely increase their number. If you have any suggestions. write to us by mail or in the comments at the bottom of this page.

JPEG images are found everywhere in our digital lives, but behind this veil of awareness lies algorithms that eliminate detail that the human eye cannot perceive. The result is the highest visual quality with the smallest file size. but how exactly does it all work? Let’s see what exactly our eyes can’t see!

It’s easy to take for granted the ability to send a photo to a friend without worrying about which device, browser, or operating system they’re using. but that wasn’t always the case. By the early 1980s, computers were able to store and display digital images, but there were many competing ideas about the best way to do this. You couldn’t just send an image from one computer to another and hope that everything would work. To address this issue, a committee of experts from around the world was assembled in 1986 called the Joint Photographic Experts Group (JPEG), a joint effort between the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC ). two international standardization organizations headquartered in Geneva (Switzerland).

A group of people called JPEG created the JPEG digital image compression standard in 1992. Anyone who has used the Internet has probably come across JPEG images. This is the most common way to encode, send and store images. From web pages to email and social media, JPEG is used billions of times a day. almost every time we view an image online or send it. Without JPEG, the web would be less vibrant, slower, and likely to have fewer pictures of cats.!

This article is about how to decode a JPEG image. In other words, what is required to convert the compressed data stored on the computer into an image that appears on the screen. It is worth knowing about this not only because it is important for understanding the technology that we use on a daily basis, but also because by uncovering the compression levels, we better know perception and vision, as well as what details our eyes are most sensitive to.

In addition, playing with images in this way is very interesting.

Discrete cosine transform and sampling

This level of compression is what defines JPEG for the most part. After converting the colors to YCbCr, the components are compressed separately, so further we can concentrate only on the Y component.And this is what the bytes of the Y component look like after applying this level.

(Interactive version. in the original article). In the interactive version, clicking on a pixel scrolls the editor to the line that denotes it. Try removing numbers from the end or adding some zeros to a specific number.

At first glance, it looks like a very bad compression. There are 100,000 pixels in an image, and 102,400 numbers are required to represent their brightness (Y-components). this is worse than compressing nothing at all!

Note, however, that most of these numbers are zero. over, all these zeros at the end of lines can be removed without changing the image. There are about 26,000 numbers left, which is almost 4 times less!

This level contains the secret of chess patterns. Unlike other effects we’ve seen, the appearance of these patterns is not a glitch. They are the building blocks of the entire image. Each line of the editor contains exactly 64 numbers, discrete cosine transform (DCT) coefficients corresponding to the intensities of 64 unique patterns.

These patterns are generated from the cosine plot. Here’s what some of them look like:

8 out of 64 odds

Below is an image showing all 64 patterns.

(Interactive version. in the original article).

These patterns are of particular importance as they form the basis of the 8×8 images. If you are unfamiliar with linear algebra, this means that any 8×8 image can be obtained from these 64 patterns. DCT is the process of dividing images into 8×8 blocks and converting each block into a combination of these 64 coefficients.

The fact that any image can be composed of 64 specific patterns seems like magic. However, this is the same as saying that any place on Earth can be described by two numbers. latitude and longitude [indicating hemispheres / approx. transl.]. We often think of the earth’s surface as two-dimensional, so we only need two numbers. An 8×8 image has 64 dimensions, so we need 64 numbers.

It is not yet clear how this helps us in terms of compression. If we need 64 numbers to represent an 8×8 image, why is this better than just storing 64 luma components? We do this for the same reason that we turned three RGB numbers into three YCbCr numbers: it allows us to remove subtle details.

It is difficult to see exactly what details are removed at this stage, since JPEG applies DCT to 8×8 blocks. However, no one forbids us to apply it to the whole picture. Here’s what the Y-component DCT looks like when applied to the whole picture:

than 60,000 numbers can be removed from the end with little or no noticeable change in the photo.

Note, however, that if we zero out the first five numbers, the difference will be obvious.

The numbers at the beginning represent low frequency changes in the image, and our eyes pick them up best. The numbers towards the end indicate treble changes that are more difficult to notice. To “see what is not visible to the eye”, we can isolate these high frequency details by zeroing the first 5000 numbers.

We see all areas of the image where the greatest change occurs from pixel to pixel. The cat’s eyes, mustache, terry blanket and shadows in the lower left corner stand out. You can go further by zeroing the first 10,000 numbers:

These high-frequency details are JPEG and are removed during the compression step. Converting colors to DCT coefficients is lossless. Loss is generated in the sampling step where high frequency or near zero values ​​are removed. When you lower the quality of JPEG saving, the program increases the threshold for the number of values ​​to remove, which results in a smaller file size, but makes the picture more pixelated. Therefore, the image in the first section, which was 57 times smaller, looked like this. Each 8×8 block was represented by much fewer DCT coefficients compared to the higher quality version.

You can do cool effect like progressive image streaming. You can display a blurry picture, which becomes more and more detailed as more and more coefficients are downloaded.

Here, just for fun, what happens with just 24,000 numbers:

Looking inside JPEG

Everything is stored on a computer as a sequence of binary numbers. Typically these bits, zeros and ones, are grouped by eight to make up bytes. When you open a JPEG image on a computer, something (browser, operating system, something else) must decode the bytes, restoring the original image as a list of colors that can be displayed.

If you download this cute cat photo and open it in a text editor, you will see a bunch of rambling symbols.

Here I am using Notepad to examine the contents of the file, as regular text editors like Notepad from Windows will mess up the binary after saving and it will no longer be JPEG compliant.

Opening an image in a text editor confuses the computer, just as you confuse your brain when you rub your eyes and start to see colored spots.!

How to Convert HEIC to JPG on iPhone

These spots you see are known as phosphenes and are not the result of stimulus from light or mind-generated hallucinations. They happen because your brain thinks that any electrical signals in your optic nerves are transmitting information about light. The brain needs to make such assumptions, because there is no way to know if a signal is sound, vision, or something else. All nerves in the body transmit exactly the same electrical impulses. By pressing on your eyes, you send signals that are not visual, but that activate receptors in the eye, which your brain interprets. in this case, incorrectly. as something visual. You are literally able to see pressure.!

It’s funny to think about how computers are like brains, but it’s also a useful analogy to illustrate how much the meaning of data. transmitted through the body by nerves or stored on a computer. depends on its interpretation. All binary data is composed of zeros and ones, basic components capable of transmitting any kind of information. Your computer often guesses how to interpret them with clues such as file extensions. Now we are forcing him to interpret them as text, since this is what a text editor expects.

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To understand how to decode JPEG, we need to see the original signals themselves. the binary data. This can be done with a hex editor, or directly on the original article web page! There is an image, next to which in the text field all its bytes (except for the title) are given, presented in decimal form. You can change them and the script will recode and produce a new image on the fly.

You can learn a lot just by playing with this editor. For example, can you tell in what order the pixels are stored?

In this example, it is strange that changing some numbers does not affect the image at all, and, for example, if you replace the number 17 with 0 in the first line, then the photo will completely deteriorate!

Other changes, for example, replacing 7 on line 1988 with 254 changes the color, but only the subsequent pixels.

Perhaps the strangest thing is that some of the numbers change not only the color but also the shape of the image. Change 70 on line 12 to 2 and look at the top row of the image to see what I mean.

And no matter what JPEG image you use, you will always find these cryptic staggered patterns when you edit bytes.

While playing with the editor, it is difficult to understand how a photo is recreated from these bytes, since JPEG compression consists of three different technologies that are applied sequentially in levels. We will examine each of them separately to uncover the mysterious behavior we are observing.

  • Color subsampling.
  • Discrete cosine transform and sampling.
  • Run length coding, delta and Huffman

So that you can imagine the scale of compression, note that the image above represents 79,819 numbers, that is, about 79 KB. If we were to store it without compression, each pixel would require three numbers. for the red, green and blue components. This would amount to 917,700 numbers, or approx. 917 Kb. As a result of JPEG compression, the final file is reduced by more than 10 times!

In fact, this image can be compressed much more. Below are two images side by side. the photo on the right was compressed to 16 KB, that is, 57 times smaller than the uncompressed version!

If you look closely, you will see that these images are not identical. Both of them are images with JPEG compression, but the right one is much smaller in volume. It also looks a little worse (look at the squares of the background colors). Therefore, JPEG is also called lossy compression; in the process of compression, the image changes and loses some details.

Color subsampling

Here is an image with only the first level of compression applied.

(The interactive version is in the original article). Removing one number destroys all colors. However, if you remove exactly six numbers, it has almost no effect on the image.

Now numbers are a little easier to decipher. This is almost a simple list of colors, in which each byte changes exactly one pixel, but at the same time it is already half the size of an uncompressed image (which would take about 300 KB in such a reduced size). Guess why?

You can see that these numbers do not represent the standard red, green and blue components, because if we replace all the numbers with zeros, we get a green image (not white).

This is because these bytes stand for Y (brightness),

Why not use RGB? After all, this is how most modern screens work. Your monitor can display any color, including red, green, and blue, with different intensities for each pixel. White is obtained by turning on all three at full brightness, and black by turning them off.

It is also very similar to how the human eye works. The color receptors in our eyes are called “cones”, and are divided into three types, each of which is more sensitive to either red, green or blue [S-type cones are sensitive in violet-blue (S from English. Short. short wave spectrum), M-type. in green-yellow (M from English. Medium. medium wave), and L-type. in yellow-red (L from English. Long. long-wave) parts of Spectra. The presence of these three types of cones (and rods that are sensitive in the emerald green part of the Spectra) give a person color vision. / approx. transl.]. Rods, another type of photoreceptor in our eyes, are only capable of detecting changes in brightness, but they are much more sensitive. There are about 120 million rods in our eyes and only 6 million cones.

Therefore, our eyes are much better at noticing changes in brightness than changes in color. By separating color from brightness, you can remove some color and no one will notice. Color subsampling is the process of representing the color components of an image at a lower resolution than the luma components. In the example above, each pixel has exactly one Y component, and each distinct group of four pixels has exactly one Cb component and one Cr component. Therefore, the image contains four times less color information than the original.

The YCbCr color space is used not only in JPEG. It was originally invented in 1938 for television broadcasts. Not everyone has a color TV, so the separation of color and brightness allowed everyone to receive the same signal, and TVs without color just used only the brightness component.

Therefore, deleting one number from the editor completely destroys all colors. Components are stored as Y Y Y Y Cb Cr (actually, not necessarily in that order. the storage order is specified in the file header). Removing the first number will cause the first Cb value to be interpreted as Y, Cr as Cb, and in general you will get a domino effect that switches all the colors of the picture.

The JPEG specification does not oblige you to use YCbCr. But in most files it is used because it produces better quality images after downsampling compared to RGB. But you don’t have to take my word for it. See for yourself in the table below how the downsampling of each individual component will look like in RGB and YCbCr.

(Interactive version. in the original article).

Removing blue is not as noticeable as red or green. This is because of the six million cones in your eyes, about 64% are sensitive to red, 32% to green and 2% to blue.

The downsampling of the Y component (bottom left) is best seen. Even a small change is noticeable.

Converting an image from RGB to YCbCr does not reduce the file size, but it makes it easier to find less visible details that can be removed. Lossy compression occurs in the second stage. It is based on the idea of ​​presenting data in a more compressible form.

Run length coding, delta and Huffman

So far, all stages of compression have gone with losses. The last stage, on the contrary, goes without losses. It does not delete information, however it significantly reduces the file size.

How can you squeeze something without discarding information? Imagine how we would describe a simple black rectangle 700 x 437.

JPEG uses 5000 numbers for this, but much better results can be achieved. Can you imagine a coding scheme that would describe such an image in as few bytes as possible.?

The smallest scheme I can think of uses four: three to represent a color, and a fourth to how many pixels are in that color. The idea of ​​representing repeated values ​​in this concise manner is called run-length encoding. It has no loss, since we can restore the encoded data in its original form.

The size of a JPEG file with a black rectangle is much larger than 4 bytes. remember that at the DCT layer, compression is applied to blocks of 8×8 pixels. Therefore, we need at least one DCT coefficient for every 64 pixels. We need one because instead of storing one DCT coefficient followed by 63 zeros, encoding the run lengths allows us to store one number and denote that “all others are zeros”.

Delta coding is a technique whereby each byte contains a difference from a value, rather than an absolute value. Therefore, editing certain bytes changes the color of all other pixels. For example, instead of storing

We could start with 12, and then just indicate how much to add or subtract to get the next number. And this sequence in delta coding takes the form:

The converted data is not smaller than the original, but it is easier to compress it. Delta coding before run length coding can help a lot while still being a lossless compression.

Delta coding is one of the few techniques used outside of 8×8 blocks. Of the 64 DCT coefficients, one is just a constant wave function (solid color). It represents the average luminance of each block for the luma components, or the average blueness for the Cb components, and so on. The first value of each DCT block is called a DC value, and each DC value is delta-coded with respect to the previous ones. Therefore, changing the brightness of the first block will affect all blocks.

The last mystery remains: how does the singular change completely spoil the whole picture? So far, compression levels have not had such properties. The answer lies in the JPEG header. The first 500 bytes contain metadata about the image. width, height, etc., and so far we have not worked with them.

Without a header, it’s almost impossible (or very difficult) to decode a JPEG. It will look like I’m trying to describe a picture to you, and I’m starting to invent words to convey my impression. The description will probably be very succinct, since I can invent words with exactly the meaning I want to convey, but for everyone else they will not make sense.

It sounds silly, but this is how it happens. Each JPEG image is compressed with codes specific to it. The code dictionary is stored in the header. This technique is called “Huffman code” and the vocabulary is called the Huffman table. In the header, the table is marked with two bytes. 255 and then 196. Each color component can have its own table.

Changes to tables will radically affect any image. A good example is to change on the 15th line 1 to 12.

This is because the tables tell you how to read individual bits. So far, we’ve only worked with decimal binary numbers. But this hides from us the fact that if you want to store the number 1 in a byte, then it will look like 00000001, since each byte must have exactly eight bits, even if only one of them is needed.

This is potentially a big waste of space if you have a lot of small numbers. Huffman code is a technique that allows us to relax this requirement that each number must be eight bits long. This means that if you see two bytes:

Then, depending on the Huffman table, it can be three numbers. To extract them, you first need to split them into separate bits:

Then we turn to the table to understand how to group them. For example, it can be the first six bits, (111010), or 58 in decimal, followed by five bits (10011), or 19, and finally the last four bits (0011), or 3.

Therefore, it is very difficult to understand the bytes at this stage of compression. The bytes do not represent what it seems. I will not delve into the details of working with the table in this article, but there are enough materials on this issue on the network.

One of the interesting tricks you can do knowing this is to separate the header from the JPEG and store it separately. In fact, it turns out that only you can proHonor the file. does this to make the files even smaller.

What else you can do is change the Huffman table quite a bit. For others, it will look like a messed up picture. And only you will know the magical way to fix it.

To summarize, what does it take to decode JPEG? It is necessary:

  • Extract Huffman table (s) from header and decode bits.
  • Extract the discrete cosine transform coefficients for each color and luminance component for each 8×8 block by performing inverse transformations of the run length and delta coding.
  • Combine cosines based on coefficients to get pixel values ​​for each 8×8 block.
  • Scale color components if downsampling was performed (this information is in the header).
  • Convert the resulting YCbCr values ​​for each pixel to RGB.
  • Display the image on the screen!

Serious work for easy viewing of a photo with a cat! However, what I like about it is that you can see how human-centered JPEG technology is. It is based on the peculiarities of our perception, allowing to achieve much better compression than conventional technologies. And now that you understand how JPEG works, you can imagine how these technologies can be transferred to other areas. For example, delta encoding in a video can lead to a significant reduction in file size, since there are often entire areas that do not change from frame to frame (for example, the background).

The code used in the article is open source and contains instructions for replacing the pictures with your own.