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| author | Michael R Sweet <michael.r.sweet@gmail.com> | 2011-02-15 15:28:27 +0000 |
|---|---|---|
| committer | Michael R Sweet <michael.r.sweet@gmail.com> | 2011-02-15 15:28:27 +0000 |
| commit | f8697125f4ac2e0690ee0e5be408ff35be29252e (patch) | |
| tree | 67d8dc37339502ef09c92971b940f35fa82ce5b0 /jpeg/usage.txt | |
| parent | 1216e9530fe541df6b95ffa39d00df9919cee4fa (diff) | |
Merge changes from JPEG 8c (released Jan 16, 2011)
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@8426 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Diffstat (limited to 'jpeg/usage.txt')
| -rw-r--r-- | jpeg/usage.txt | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/jpeg/usage.txt b/jpeg/usage.txt index 6e8546a6a..eae58425f 100644 --- a/jpeg/usage.txt +++ b/jpeg/usage.txt @@ -87,8 +87,9 @@ The basic command line switches for cjpeg are: -progressive Create progressive JPEG file (see below). -scale M/N Scale the output image by a factor M/N. Currently - supported scale factors are 8/N with all N from 1 to - 16. + supported scale factors are M/N with all N from 1 to + 16, where M is the destination DCT size, which is 8 by + default (see -block N switch below). -targa Input file is Targa format. Targa files that contain an "identification" field will not be automatically @@ -150,6 +151,19 @@ file size is about the same --- often a little smaller. Switches for advanced users: + -block N Set DCT block size. All N from 1 to 16 are possible. + Default is 8 (baseline format). + Larger values produce higher compression, + smaller values produce higher quality + (exact DCT stage possible with 1 or 2; with the + default quality of 75 and default Luminance qtable + the DCT+Quantization stage is lossless for N=1). + CAUTION: An implementation of the JPEG SmartScale + extension is required for this feature. SmartScale + enabled JPEG is not yet widely implemented, so many + decoders will be unable to view a SmartScale extended + JPEG file at all. + -dct int Use integer DCT method (default). -dct fast Use fast integer DCT (less accurate). -dct float Use floating-point DCT method. |