Images

Changing colours with ImageMagick

Converting true black rgb(0,0,0) in an image to rgb(0,0,10) to force composite black:

name=MyLogoImage.png
convert "$name" -depth 32 -type TrueColorMatte -alpha set -channel RGBA -fill 'rgb(0,0,10)' -opaque 'rgb(0,0,0)' "PNG32:new-$name"

This will create a file called new-MyLogoImage.png that should have the same properties shown by the file command. The difference will be that the black is no longer true black and is suitable for use with LG Plates.

MyLogoImage.png: PNG image data, 522 x 97, 8-bit/color RGBA, non-interlaced

The RGBA provides the alpha channel (partial transparency) which is sometimes used for smoother edges rather than using shades of the main colour.

A similar command could be used to -fill 'rgb(250,250,250)' -opaque 'rgb(255,255,255)' replace pure white with off-white for use with a Pro printer. There may be some fuzzing required (-fuzz 5% for example) where badges use a shade of white such as rgb(253,253,253) since this wouldn't be picked up as exactly rgb(255,255,255) but would still be translated by the printer into transparency. The actual fuzz value may need some experimentation.

Extend image and fill new canvas

Extend the file to 590x4015 from whatever the current size is. Centre the original image on the new canvas and fill the extra canvas with solid blue (#0000ff). The new image has the colour depth adjusted to the minimum so it's quite a good way of shrinking the files.

-rw-rw-r-- 1 plates plates 11216 Nov 14 12:14 Union Flag Eng 2.png
Union Flag Eng 2.png: PNG image data, 590 x 2480, 8-bit colormap, non-interlaced

convert "$name" -background blue -gravity Center -depth 32 -extent '590x4015' "new-$name"

-rw-r--r-- 1 plates plates  4640 Dec 14 15:52 new-Union Flag Eng 2.png
new-Union Flag Eng 2.png:     PNG image data, 590 x 4015, 2-bit colormap, non-interlaced

Convert transparent background to white

Replace white with any other colour as required!

convert transparentbgimage.png -transparent-color white -background white -layers flatten -depth 32 outputimage.png

Colour Picker app

Highly recommended! http://instant-eyedropper.com/

Contact Sheet with ImageMagick

montage -verbose -label '%f' -pointsize 14 \
   -background 'white' -fill 'black' \
   -define jpeg:size=300x300 -geometry 300x300+2+2 \
   -auto-orient *.png ../output.png

-label '%f' specifies to use the filename as a label for each image -tile 10x makes it output 10 badges per row

Count the unique colours in an image

This can be useful if an image won't reduce in size by much (e.g to an 8 bit colour map).

$ file MyImage.png
MyImage.png:     PNG image data, 400 x 400, 8-bit/color RGB, non-interlaced

ImageMagick has a command to count how many colours there are in an image:

$ identify -format %k MyImage.png
2310