update

[l4.git] / l4 / pkg / libjpeg / lib / contrib / usage.txt

diff --git a/l4/pkg/libjpeg/lib/contrib/usage.txt b/l4/pkg/libjpeg/lib/contrib/usage.txt
index 6e8546a6a4b04de982826768a3ba632becfbfea3..eae58425f0fcf8e19862f6358d2ab85b2656a12a 100644 (file)
--- a/l4/pkg/libjpeg/lib/contrib/usage.txt
+++ b/l4/pkg/libjpeg/lib/contrib/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.