FAQ: Why do the colours of the PNG file not match CSS colours?

This is probably caused by some embedded colour space information; see below for how to remove this.

HOWTO: Remove color space information from PNG files (pngcrush)

(You might want to do this to ensure that PNG colours match CSS colours.)

$ pngcrush -rem gAMA -rem cHRM -rem iCCP -rem sRGB infile.png outfile.png

See

http://hsivonen.iki.fi/png-gamma/

(Or, convert to GIF...)

HOWTO: (Losslessly) compress PNGs (pngcrush)

$ pngcrush image.png -rem alla -reduce result.png

See

http://developer.yahoo.net/blog/archives/2008/03/yahoos_latest_p.html

TIP: ImageMagick tips

See

http://www.cit.gu.edu.au/~anthony/graphics/imagick/

HOWTO: Convert string to image using TrueType font (ImageMagick)

Text on command line:

$ convert -background white -fill black -font ~/Library/Fonts/P22UNDER.TTF \
  -transparent white -pointsize 72 label:"Holloway Rd" holloway.gif

Text in file:

$ convert -background white -fill black -font ~/Library/Fonts/P22UNDER.TTF \
  -transparent white -pointsize 72 label:@holloway.txt holloway.gif

(This does do anti-aliasing, but I couldn't get a separate "matte" colour working...)

HOWTO: Crop an image (ImageMagick)

$ convert -mattecolor black src.jpg -crop 70x70+0+0 -size 70x70 +repage dst.jpg

ImageMagick 6+ use the "new" command-line parameter handling--the hard bit is to make sure the different bits are specified in the right order!

HOWTO: Mark a particular color as "transparent"

(Known as "Color to Alpha" in gimp.)

Use imagemagick:

$ convert -transparent white foo.png bar.png

(I don't know how to do this with Pixelmator.)

HOWTO: Strip comments from JPEGs (jpegtran)

$ jpegtran -copy none -optimize -perfect src.jpg dst.jpg

See

http://developer.yahoo.net/blog/archives/2008/03/yahoos_latest_p.html

HOWTO: Create contact sheets from video

i.e. extract frames/thumbnails from video.

Use QuickTime export function with the "Movie to Image Sequence" option. Enter a very small number of frames per second, like 0.01. Then, invoke ImageMagick's montage with options like:

$ montage *.jpg -tile 3x -geometry 300x+0+0 montage.jpg

If you get some errors like

sh: gs: command not found
montage: unable to read font (null)' @ annotate.c/RenderFreetype/1316.

just ignore them--chances are montage.jpg has successfully been created.

This will create a contact sheet of all the *.jpg images in the current directory, with three columns (and however many rows are required), resizing the images to exactly 300 pixels wide (and however many pixels high required to maintain the correct aspect ratio) with no border.

For more information on the various options, see http://www.imagemagick.org/Usage/montage/.

HOWTO: Create contact sheets from a directory of thumbnails from

different images

BROKEN! Doesn't work for filenames with spaces in the name!

$ for f in ls | perl -pe 's/\d+.png$//' | uniq ; do montage $f* -tile 3x -geometry 300x+0+0 $f.jpg ; done