How to identify a grayscale image (with threshold)?

[codeswitch]

I know how to find out if an image is a true color image or a grayscale image.

But what I'd like to have is the solution on how to identify for example this image: http://www.pitopia.de/scripts/pictures/ ... D=2&view=1 as a grayscale image.

The whole picture is black and white, except for the eyes which are green. For people it's still black and white.

Is there maybe a solution anywhere on the web? I can't find anything useful. I hope you can inspire me somehow .

[fmw42]

if there is any color in the image, any statistics such as class or type will tell you it is color and not grayscale.

I think you only hope is to analyze the histogram and decide if there is less than some total percent color other than black or white in the image.

[anthony]

Read in the image, make a clone whcih you greyscale. now compare the original image with the grayscale clone. any differences present is non grayscale color.

see...
Sorting Images by Type, Gray-scale vs Color
http://www.imagemagick.org/Usage/compare/#type_general

I have updated that part with a 'saturation test'

Saturation Test
convert rose: granite: \
-colorspace HSB -channel G -separate +channel \
-format 'avg=%[mean] peak=%[maximum]' info:

rose: -> avg=28750.1 peak=59881
granite: -> avg=1918.87 peak=3490

Numbers are relative to QuantumRange (which in my IM Q16 is 65535)
Note that both have a avg that is about 1/2 that of the peak.
With rose: being very colorful, while granite: only has about 5% color.

The a large difference than 1/2 between the average and peak, would-
indicate small patches of color. Thresholding the saturation channel
can generate a mask of the color area.

[codeswitch]

Well, thank you very much, but it's a little too complicated for me. I hoped for an easy solution.

But never mind, I using PHP itself to do it. It's not perfect, but it'll do.

If anyone wants the code I'll post it here to be discussed.

[divptl]

Hi i am trying to have the code Anthony wrote above work but i keep getting error " convert: unable to open image 'avg-

i am not getting the results he has above. Any help will be appropriated.

I CD to the folder and I have rose and granite both in the ImageMagic dir and trying to run below.

convert rose: granite: \-colorspace HSB -channel G -separate +channel \-format 'avg=%[mean] peak=%[maximum]' info:

[divptl]

Over all i need to separate gray scale image from color but has some color pix in the mix.

[snibgo]

What version IM? On what platform?

Code: Select all

convert rose: granite: \-colorspace HSB -channel G -separate +channel \-format 'avg=%[mean] peak=%[maximum]' info:

Why does your command contain backslashes?

... and I have rose and granite both in the ImageMagic dir ...

That doesn't make sense. "rose:" and "granite:" (both with colons) are built into IM.

[divptl]

I have the latest version of IM 7.0.6. I am attempting to do same what Anthony did. i kept the blackslashes and removed the line brake from below.
"
Saturation Test
convert rose: granite: \
-colorspace HSB -channel G -separate +channel \
-format 'avg=%[mean] peak=%[maximum]' info:

rose: -> avg=28750.1 peak=59881
"

[divptl]

I have the latest version of IM 7.0.6. I am attempting to do same what Anthony did. i kept the blackslashes and removed the line brake from below.
"
Saturation Test
convert rose: granite: \
-colorspace HSB -channel G -separate +channel \
-format 'avg=%[mean] peak=%[maximum]' info:

rose: -> avg=28750.1 peak=59881
"

[fmw42]

There is no %[maximum] it is %[max] (see http://www.imagemagick.org/script/escape.php). Try

Code: Select all

magick rose: granite: \
-colorspace HSB -channel G -separate +channel \
-format 'avg=%[mean] peak=%[max]\n' info:

avg=28750.1 peak=59881
avg=1918.71 peak=3490.03

[divptl]

Thank you it worked however my grayscale image has some colors in it and i will have to go on another rout. Is there a way to identify like Image generated out of a Patent software vs actual picture taken from camera ? i have no image property to relay on.

[fmw42]

See viewtopic.php?f=1&t=16201#p148602

Code: Select all

convert mostly_gray.png -colorspace HCL -channel green -separate +channel -format "%[fx:100*mean]\n" info:

4.2631

So this image contains 4% non-grayscale colors.

A true grayscale image with no color, such as a white to black gradient will have a result of zero.

Code: Select all

convert -size 256x256 gradient: -colorspace HCL -channel green -separate +channel -format "%[fx:100*mean]\n" info:

0

[divptl]

Thank you that works. Any way to tell if its graphic vs picture ? Unfortunately with threshold i am still getting color images in to gray scale because they only have three colors .

[divptl]

On more question . do you know how would i go about implementing "convert mostly_gray.png -colorspace HCL -channel green -separate +channel -format "%[fx:100*mean]\n" info:" in c# ?

[divptl]

i want to utilize the output to move file if it's above or below threshold.