diff options
| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2009-04-26 20:18:12 +0000 |
|---|---|---|
| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2009-04-26 20:18:12 +0000 |
| commit | 4ee0e1dcfc013a10729bc0512c0bee14ad480967 (patch) | |
| tree | 478b9f1574f4080409dfd4c603edec9d52b587c4 /pnmremap.html | |
| parent | ca9d1542c6311b33006250e0845996b233cfc3d5 (diff) | |
| download | netpbm-mirror-4ee0e1dcfc013a10729bc0512c0bee14ad480967.tar.gz netpbm-mirror-4ee0e1dcfc013a10729bc0512c0bee14ad480967.tar.xz netpbm-mirror-4ee0e1dcfc013a10729bc0512c0bee14ad480967.zip | |
"miscellaneous update"
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@900 9d0c8265-081b-0410-96cb-a4ca84ce46f8
Diffstat (limited to 'pnmremap.html')
| -rw-r--r-- | pnmremap.html | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/pnmremap.html b/pnmremap.html index 6641929f..d95f9c5c 100644 --- a/pnmremap.html +++ b/pnmremap.html @@ -2,7 +2,7 @@ <HTML><HEAD><TITLE>Pnmremap User Manual</TITLE></HEAD> <BODY> <H1>pnmremap</H1> -Updated: 19 February 2009 +Updated: 26 April 2009 <BR> <A HREF="#index">Table Of Contents</A> @@ -185,16 +185,22 @@ This names the file that contains the palette image. <DT><B>-fs</B> <DT><B>-nofloyd</B> <DT><B>-nofs</B> + <DD> -These options determine whether Floyd-Steinberg dithering is done. -Without Floyd-Steinberg, the selection of output color of a pixel is based -on the color of only the corresponding input pixel. With Floyd-Steinberg, -multiple input pixels are considered so that the average color of an area -tends to stay more the same than without Floyd-Steinberg. For example, -if you map an image with a black, gray, gray, and white pixel -adjacent, to a palette that contains only black and white, it might -result in an output of black, black, white, white. Pixel-by-pixel -mapping would instead map both the gray pixels to the same color. +These options determine whether <b>pnmremap</b> does Floyd-Steinberg +dithering. Without Floyd-Steinberg, <b>pnmremap</b> selects the output color +of a pixel based on the color of only the corresponding input pixel. With +Floyd-Steinberg, <b>pnmremap</b> considers regions of pixels such that the +average color of a region is the same in the output as in the input. The +dithering effect appears as a dot pattern up close, but from a distance, the +dots blend so that you see more colors than are present in the color map. + +<p>As an example, if your color map contains only black and white, and +the input image has 4 adjacent pixels of gray, <b>pnmremap</b> with +Floyd-Steinberg would generate output pixels black, white, black, white, +which from a distance looks gray. But without Floyd-Steinberg, +<b>pnmremap</b> would generate 4 white pixels, white being the single-pixel +approximation of gray. <p>Floyd-Steinberg gives vastly better results on images where unmodified quantization has banding or other artifacts, especially @@ -206,6 +212,12 @@ synonym for <B>-nofloyd</B>. <P>The default is <B>-nofloyd</B>. +<p>Before Netpbm 10.46 (March 2009), dithering doesn't work quite as you +expect if the color map has a lower maxval than the input. <b>pnmremap</b> +reduces the color resolution to the color map's maxval before doing any +dithering, so the dithering does not have the effect of making the image, +at a distance, appear to have the original maxval. In current Netpbm, it +does. <dt><b>-norandom</b> |