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JPEG compression options -- can anybody explain?
When I save a file as jpeg, I understand basic compression and quality (I
might save as 90% quality or 10% compression, for example; of course I save as TIFF or other lossless format for editing and prints). But there are lots of other JPEG compression options I do not understand -- amount of "smoothing" (0-100); checkboxes to activate "optimize" and "progressive"; "subsampling" choices of: "2x2,1x1,1x1", "2x2,1x1,1x1 (4:2:2)", "1x1,1x1,1x1",; "DCT Method (speed/quality tradeoff)" choices of: Integer, Fast Integer, Floating Point. Can anybody explain these option for fine tuning the saving of a JPEG image, or direct me to a website that might explain the best such settings for JPEG image saving? -- "It said it needed Windows98 or better installed, so I installed Linux." |
#2
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JPEG compression options -- can anybody explain?
http://www.photo.net/learn/jpeg/
"Beowulf" wrote in message news When I save a file as jpeg, I understand basic compression and quality (I might save as 90% quality or 10% compression, for example; of course I save as TIFF or other lossless format for editing and prints). But there are lots of other JPEG compression options I do not understand -- amount of "smoothing" (0-100); checkboxes to activate "optimize" and "progressive"; "subsampling" choices of: "2x2,1x1,1x1", "2x2,1x1,1x1 (4:2:2)", "1x1,1x1,1x1",; "DCT Method (speed/quality tradeoff)" choices of: Integer, Fast Integer, Floating Point. Can anybody explain these option for fine tuning the saving of a JPEG image, or direct me to a website that might explain the best such settings for JPEG image saving? -- "It said it needed Windows98 or better installed, so I installed Linux." |
#3
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JPEG compression options -- can anybody explain?
Beowulf wrote:
When I save a file as jpeg, I understand basic compression and quality (I might save as 90% quality or 10% compression, for example; of course I save as TIFF or other lossless format for editing and prints). But there are lots of other JPEG compression options I do not understand -- amount of "smoothing" (0-100); checkboxes to activate "optimize" and "progressive"; "subsampling" choices of: "2x2,1x1,1x1", "2x2,1x1,1x1 (4:2:2)", "1x1,1x1,1x1",; "DCT Method (speed/quality tradeoff)" choices of: Integer, Fast Integer, Floating Point. Can anybody explain these option for fine tuning the saving of a JPEG image, or direct me to a website that might explain the best such settings for JPEG image saving? Smoothing -- artificially blurs the whole photo such an amount. It can help compressibility as JPEG works very well with smooth gradients of color; sharp edges tend to work against it. Optimize -- does a few reordering and newer optimizations to affect file size without affecting quality. Progressive -- creates a multi-resolution image that is "progressively" downloaded and decoded as to allow a web browser with a slow connection to preview part of the graphic. i.e. Goes from no detail and pixelated to full resolution as it's downloaded. Subsampling -- what blocksize it operates on. 1x1 will give you the sharpest image, but may bloat the file size unnecessarily. Use only for computer generated and rendered material. 4:2:2 should always be used for photos. 2x2 is useful only when either recompressing a previous JPEG or when there is little sharp detail at all (like thumbnails or bad material). DCT Method -- Accuracy of the DCT algorithem. Use Floating Point always. Speed of the jpeg algorithem is generally a non-issue and you shouldn't ever have to use an integer format unless you're creating a grpahic for a integer processor only device. Effects image quality also. Colors become blocky and inaccurate with lower accuracy. |
#4
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JPEG compression options -- can anybody explain?
Beowulf wrote:
When I save a file as jpeg, I understand basic compression and quality (I might save as 90% quality or 10% compression, for example; of course I save as TIFF or other lossless format for editing and prints). But there are lots of other JPEG compression options I do not understand -- amount of "smoothing" (0-100); checkboxes to activate "optimize" and "progressive"; "subsampling" choices of: "2x2,1x1,1x1", "2x2,1x1,1x1 (4:2:2)", "1x1,1x1,1x1",; "DCT Method (speed/quality tradeoff)" choices of: Integer, Fast Integer, Floating Point. Can anybody explain these option for fine tuning the saving of a JPEG image, or direct me to a website that might explain the best such settings for JPEG image saving? Smoothing -- artificially blurs the whole photo such an amount. It can help compressibility as JPEG works very well with smooth gradients of color; sharp edges tend to work against it. Optimize -- does a few reordering and newer optimizations to affect file size without affecting quality. Progressive -- creates a multi-resolution image that is "progressively" downloaded and decoded as to allow a web browser with a slow connection to preview part of the graphic. i.e. Goes from no detail and pixelated to full resolution as it's downloaded. Subsampling -- what blocksize it operates on. 1x1 will give you the sharpest image, but may bloat the file size unnecessarily. Use only for computer generated and rendered material. 4:2:2 should always be used for photos. 2x2 is useful only when either recompressing a previous JPEG or when there is little sharp detail at all (like thumbnails or bad material). DCT Method -- Accuracy of the DCT algorithem. Use Floating Point always. Speed of the jpeg algorithem is generally a non-issue and you shouldn't ever have to use an integer format unless you're creating a grpahic for a integer processor only device. Effects image quality also. Colors become blocky and inaccurate with lower accuracy. |
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