How to check for empty (mono-color) image?

[graceman9]

subj.
For example, I cut the picture on the tiles, and I want to know which of them are empty? (transparent, or the same color). Thanks for the replies.

[fmw42]

get the standard-deviation from the verbose statistics for each tile. If the standard deviation is 0, then the image is one color. You may have to look channel by channel including the alpha channel.

Alternate is to use string formats. See http://www.imagemagick.org/script/escape.php


convert image -format "%[standard_deviation]" info:

returns values between 0 and QuantumRange (255 for 8-bit or 65535 for 16-bit IM compiles0

or

convert image -format "%[fx:u.standard_deviation]" info:

returns values between 0 and 1

[anthony]

Number of colors %k will also do this! If you have one unique color then it will be 1

[graceman9]

convert image -format "%[standard_deviation]" info:

Not work for me. I also try

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identify -format %[standard-deviation]

but two same (empty and transparent images, size 450 and 452 bytes) give different results:

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$ identify -format %[standard-deviation] 1.png
11571.2
$ identify -format %[standard-deviation] 2.png 
7529.32

MY TWO TRANSPARENT IMAGES BELOW:


I see no difference in eog or gimp, but when I upload image i saw this (white lines in top of image):
http://pic.lg.ua/s/g/0YCfF/DYPSF

Number of colors %k will also do this! If you have one unique color then it will be 1

Yes, it is!

And new question: how can I diff "white mono-color image" from "gray mono-color image" ?

[fmw42]

see -compose minus or -compose different or compare

http://www.imagemagick.org/Usage/compose/#minus
http://www.imagemagick.org/Usage/compose/#difference

http://www.imagemagick.org/Usage/compare/

Can you be more specific about what type of compare you want -- what kind of result -- an image or a number

[graceman9]

Excuse me for the delay in replying.
I need the result - a number.
That's what I found:

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alpha=`convert $f -resize 1x1 txt: | sed '1d' | sed 's/\([^)]*\).*/\1/' | sed 's/,/ /g' | awk '{print $NF}'`

But I still want to do this without "sed" expression any advice?

[anthony]

And new question: how can I diff "white mono-color image" from "gray mono-color image" ?

Just crop a single pixel from the image and output a TXT: image.

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  convert image.png  -crop 1x1+0+0 txt:

See TXT: image file format and Extracting Image Color

OR just get IM to print the images 0,0 color using -format and info:

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  convert image.png -format "%[pixel:s]" info:

See info: identify output and FX Expressions as Escapes

With one image you can also -print (only outputs its formatted string once, not once per image.

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  convert image.png  -print "%[pixel:s]" null:

See Formated Text Output Options