JPEG

JPEG or JPG, is an electronic image format created by the Joint Photographic Experts Group in 1992. The format uses a discrete cosine transform to achieve lossy compression which can reduce typical photographs to about 1/10th their original size with minor visual degradation. In 2000, the Joint Photographic Experts Group tried to replace the format with a superior JPEG 2000 format, but few programs adopted it since it was only marginally better than the original. The format has native support in every major operating system and Web browser. Although the format is still especially popular, it is slowly being replaced by the lossy encoding of WEBP which compresses at a noticeably better rate and supports a lot of new features, and is now the official Internet lossy bitmap graphic format.

Media

Videos

How JPEG compression works.

Software

The following programs support JPEG in some capacity.

Program	Type	Notes
Corel Photo-Paint	Raster Editor	Supports many different format options including JPEG 2000.
GraphicsGale	Raster Editor	Supports some features.
Paint.net	Raster Editor	Supports some features.
ImageMagick	Raster Programmer	Programmably create images. Supports pretty much every format option, including JPEG 2000.
IrfanView	Image Viewer	Can open and display JPEG images. Can perform some modifications without losing quality.
PabloDraw	Image Viewer	Can open and display JPEG images.
JPEGOptim	Compression Optimizer	Can decrease file size without losing quality, or decrease it more with a quality loss.
LibreOffice	Document Editor	Can import and export to JPEG.
Corel Draw	Vector Editor	Can import and export to JPEG.
Inkscape	Vector Editor	Can import and export to JPEG.
XPDF	Image Extractor	Can extract JPEG images from PDF files.
foobar2000	Jukebox	Primary format for embedded album art.

Interlacing

JPEG has a feature which, although not technically interlacing, has a similar utility to interlacing. However, like actual interlacing, it typically increases the size of the image.

Compression Examples

Because JPEG images are based on waveforms rather than pixels, their file size is tied both to the quality of the rendered output and the intricacy of the image. Below I examine how artifacting is expressed with the decrease in quality. Each image was compressed using the JPEG compressor in Corel Photo-Paint X7.

Uncompressed (769 KB)

This is the test image. It combines a photograph, text, gradients, checkerboards, and a screenshot so you can see how JPEG compression acts on each graphic structure. The image is 512x512 pixels with a 24-bit color depth, resulting in an uncompressed size of 786,432 bytes.

100% JPEG Quality (234 KB)

This is the same image using JPEG compression at 100% quality. Although the file size has dropped to 238,998 bytes, less than a third of the size of the original, the quality is nearly identical. Unless a person were told, they might easily mistake this for the uncompressed image. Only someone with a keen eye for compression artifacts would spot them in the red gradient. In JPEG compression, the color red always degrades the most.

85% JPEG Quality (96 KB)

At 85% quality the resulting image is only 98,303 bytes, eight times smaller than the original, and compression artifacts are still barely noticeable. Hints of artifacting can be seen around the text and color loss is just starting to be noticeable in the Super Mario Bros. screenshot.

50% JPEG Quality (59 KB)

Now at only 50% quality, the file size has dropped to 59,927 bytes, over 13 times smaller than the original, however, the quality has taken severe drop. The photo is clearly not as crisp and the text, though still readable, has a lot of visible noise around it. The gradients are getting a little choppy, the white squares in the checkerboards are getting messy, and all the sharp contrast changes in the screenshot leave significant artifacts.

25% JPEG Quality (43 KB)

At 25% quality, we're now seeing diminishing returns. We've only saved about 16,000 bytes, but the appearance has suffered drastically. The file is now 43,675 bytes, about 18 times smaller than the original. The photo now looks awful, the text has so much noise, it's hard to read, the gradients have obvious color banding, the checkerboards are quite messy, and the screenshot looks like garbage.

10% JPEG Quality (30 KB)

At 10% quality, we've only saved another 13,000 bytes, but the image is practically unusable for any of the four types. There is clear blocking and color banding all over the image, and the text can easily be misread. The image is only 30,242 bytes in size, but it doesn't matter much at this point.

5% JPEG Quality (24 KB)

At 5% quality, the image is a mere 24,283 bytes, but it's an absolute mess. Most of the text is unreadable, the the face is hugely distorted, the color is in big chunks and, in many places, very off.

1% JPEG Quality (21 KB)

At 1% quality, the image is only 21,285 bytes, 38 times smaller than the original, but it's wasted data. The face is so bad, it's unrecognizable, the text is illegible, and the other graphics are just as bad. Describing the image with text would take less space.

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