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 JPEG compression...

These images show the effects of JPEG compression on image quality and file size. JPEG is "lossy"—each save loses some image quality. While many image editors let you set the degree of compression with a "Quality" percentage, their scales are not standard (50% in one editor may not yield the same image quality or file size as 50% in another editor), and the scale numbers are arbitrary (50% does not mean "save 50% of the information" nor "save 50% of the file size").

The first 16 images show the effect of saving at increasing quality settings. The file names show the quality % as the first number and the file size in KB as the second number (e.g., books.40.44.jpg shows that at 40% quality the file size is 44KB).

The next image shows a small portion of many of the images at 3 times normal size to better show the differences.

The chart shows how file size increases as the quality % increases. While these numbers apply only to this image, the shape of the curve suggests the file size changes to expect with any image.

The images show there is no visible advantage in specifying a quality greater than 50% for use on the web, and the chart shows file size increases dramatically beyond 70%. Never choose a quality of 100%, since the file size can be larger than the uncompressed original and gives no better quality than lower percentages.

Two images after the chart show the loss of image quality due to "lossy" JPEG compression. The last two images demonstrate the web standard of displaying images at 72 pixels per inch.

An excellent interactive JPEG tutorial shows the effects of JPEG compression and describes how JPEG compression is done. Choose the Mosquito Antennae example and watch the blue area at the upper right to clearly see the degradation as you increase the degree of JPEG compression.

books.0.8.jpg
books.0.8.jpg
books.1.8.jpg
books.1.8.jpg
books.5.12.jpg
books.5.12.jpg
books.10.20.jpg
books.10.20.jpg
books.15.24.jpg
books.15.24.jpg
books.20.28.jpg
books.20.28.jpg
books.25.32.jpg
books.25.32.jpg
books.30.35.jpg
books.30.35.jpg
books.40.44.jpg
books.40.44.jpg
books.50.50.jpg
books.50.50.jpg
books.60.56.jpg
books.60.56.jpg
books.70.68.jpg
books.70.68.jpg
books.80.84.jpg
books.80.84.jpg
books.90.120.jpg
books.90.120.jpg
books.95.164.jpg
books.95.164.jpg
books.100.312.jpg
books.100.312.jpg
books.composite.60.18.jpg
books.composite.60.18.jpg
JPEGcompression.jpg
JPEGcompression.jpg
books.10x25.jpg
books.10x25.jpg
books.compare.300pct.jpg
books.compare.300pct.jpg
AiryFairy288.1x1.80.jpg
AiryFairy288.1x1.80.jpg
AiryFairy72.4x4.80.jpg
AiryFairy72.4x4.80.jpg
 image miscellany...
 image miscellany...