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Diffstat (limited to 'src/3rdparty/libjpeg/usage.txt')
| -rw-r--r-- | src/3rdparty/libjpeg/usage.txt | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/src/3rdparty/libjpeg/usage.txt b/src/3rdparty/libjpeg/usage.txt index 6e8546a6a4..eae58425f0 100644 --- a/src/3rdparty/libjpeg/usage.txt +++ b/src/3rdparty/libjpeg/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. |