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File Format Specifications

What is a JPEG file?

A JPEG is a type of image format that is saved using the method of lossy compression. The đầu ra image, as result of compression, is a trade-off between storage kích thước and image quality. Users can adjust the compression màn chơi to achieve the desired unique level while at the same time reduce the storage size. Image quality is negligibly affected if 10:1 compression is applied to the image. The higher the compression value, the higher the degradation in image quality.

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File Format Specifications

JPEG image file format was standardized by the Joint Photographic Experts Group and, hence, the name JPEG. The format has been the choice of storing and transmitting photographic images on the web. Almost all Operating systems now have viewers that support visualization of JPEG images, which are often stored with JPG extension as well. Even the web browsers support visualization of JPEG images. Before going into the JPEG file format specifications, the overall process of steps involved in JPEG creation need to be mentioned.

JPEG Compression Steps

Transformation: Color images are transformed from RGB into a luminance/chrominance image (Eye is sensitive lớn luminance, not chrominance, so that chrominance part can thua much data và thus can be highly compressed.

Down Sampling: The down sampling is done for colored component và not for luminance component .Down sampling is done either at a ratio 2:1 horizontally và 1:1 vertically (2h 1 V). Thus the image reduces in kích thước since the ‘y’ component is not touched, there is no noticeable loss of image quality.

Organizing in Groups: The pixels of each color component are organized in groups of 8×2 pixels called “ data units” if number of rows or column is not a multiple of 8, the bottom row và rightmost columns are duplicated.

Discrete Cosine Transformation: Discrete Cosine Transform ( DCT) is then applied khổng lồ each data unit lớn create 8×8 maps of transformed components.DCT involves some loss of information due khổng lồ the limited precision of computer arithmetic. This means that even without the map there will be some loss of image chất lượng but it is normally small.

Quantization: Each of the 64 transformed components in the data unit is divided by a separate number called its ‘Quantization Coefficient (QC)’ and then rounded lớn an integer. This is where information is lost irretrievably, Large QC cause more loss. In general, the most JPEG implements allow use QC tables recommended by the JPEG standard.

Encoding: The 64 quantized transformed coefficients ( Which are now integers) of each data unit are encoded using a combination of RLE & Huffman coding.

Adding Header: The last step adds header & all the JPEG parameters used and output the result.

The JPEG decoder uses the steps in reverse to lớn generate the original image from the compressed one.

File Structure

A JPEG image is represented as a sequence of segments where each segment begins with a marker. Each marker starts with 0x
FF byte followed by marker flag khổng lồ represent the type of marker. The payload followed by marker is different as per marker type. Common JPEG marker types are as listed below:

Short Name
FF, 0x
noneStart of Image
FF, 0x
variable sizeStart of Frame
FF, 0x
variable sizeStart fo Frame
FF, 0x
variable sizeDefine Huffman Tables
FF, 0x
variable sizeDefine Quantization Table(s)
FF, 0x
4 bytesDefine Restart Interval
FF, 0x
variable sizeStart Of Scan
FF, 0x
FF, 0x
variable sizeApplication specific
FF, 0x
variable sizeComment
FF, 0x
noneEnd Of Image

Within the entropy-coded data, after any 0x
FF byte, a 0x00 byte is inserted by the encoder before the next byte, so that there does not appear khổng lồ be a marker where none is intended, preventing framing errors. Decoders must skip this 0x00 byte. This technique, called byte stuffing (see JPEG specification section F.1.2.3), is only applied to the entropy-coded data, not khổng lồ marker payload data. Chú ý however that entropy-coded data has a few markers of its own; specifically the Reset markers (0x
D0 through 0x
D7), which are used khổng lồ isolate independent chunks of entropy-coded data lớn allow parallel decoding, and encoders are free to insert these Reset markers at regular intervals (although not all encoders bởi vì this).

JPEGView is a lean, fast và highly configurable viewer/editor for JPEG, BMP, PNG, WEBP, TGA, GIF và TIFF images with a minimal GUI. Basic on-the-fly image processing is provided - allowing adjusting typical parameters as sharpness, color balance, rotation, perspective, contrast and local under-/overexposure.


Small and fast, uses SSE2 & up lớn 4 CPU cores
High unique resampling filter, preserving sharpness of images
Basic image processing tools can be applied realtime during viewing
Movie mode khổng lồ play folder of JPEGs as movie


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This is *exactly* what I've been looking for. Extremely lightweight & highly customizable. Supports executing custom commands on custom hotkeys. And the shadow removing mode (Ctrl+L) is very useful.

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The Most Promising Viewer I've tested so far, và I've tested a dozen or so. I'm amazed I hadn't seen this one before! But khổng lồ be fair, I've only recently started to lớn look in alternative viewers after having used Thumbs
Plus & Total Commander for decades.Blazingly fast, powerful commands, supremely configurable, truly portable in Global Configuration Mode (why isn't all software không lấy phí from the tyranny of Registry Lock-In & the mess of files they leave all around the system), easy to lớn learn... What isn't there to lớn love?
It's chất lượng on-the fly tự động hóa correction feature is amazing for viewing less than perfect but otherwise properly taken pictures, in many cases saving you the trouble of editing them.With all its great features, it is missing a few that would make this the killer viewer app.The most important is the browser. You can't browse a folder to select which one khổng lồ view - you need to enter into a folder using the Windows Explorer file picker and simply view each tệp tin in sequence after that and if you get out, the application quits. Thank God for shortcuts!It is also missing the ability to lớn show videos or play play audio comments with pictures (an essential feature for us old timers who've gotten used lớn record audio notes & background sounds with pictures). Also, it would be great if it could view a few other common file formats such as .psd và vector formats .emf .wmf & .svg
Editing features I'd love khổng lồ see is the ability lớn directly edit Picture Comments (the old JPEG format, the more recent "User
Comment" or its modern Microsoft Incarnation, XPComment), the ability to time-stamp the edited tệp tin to its original date taken.The only viewer interface enhancement I would love khổng lồ see is the ability to lớn customize the tệp tin info panel, so as to lớn be able khổng lồ select what info to lớn show in toggle (such as filename, filename và date taken, filename, date taken and comment or full picture taking data), how (font color, background màu sắc and transparency and its position on the screen).Speedy, customizable & powerfully coded as it is, with the few enhancements suggested it truly has the potential of replacing every other viewer out there, whether không tính phí or not.Kudos for the amazing work so far!Sorry for the lack of legibility, shthcm.edu.vn apparently lacks the ability to lớn show comments with its original paragraph formatting intact.

Additional Project Details

Operating Systems
Romanian, Korean, French, Ukrainian, Polish, Czech, Italian, Greek, English, Portuguese, Belarusian, Swedish, Brazilian Portuguese, Chinese (Simplified), German, Japanese, Spanish, Russian, Basque (Euskara)Intended Audience
End Users/Desktop
User Interface
Win32 (MS Windows)Programming Language