Legacy ImageMagick Discussions Archive

Hi,

I have an image with following info:

gray.jpg JPEG 12558x8776 12558x8776+0+0 8-bit PseudoClass 256c 1.937MB 0.000u 0:00.000

I am using identify to get mean gray value and standard deviation of this image:

identify -format %[mean]%[standard-deviation] gray.jpg

The results returned are: 65535, 1396.33

Why is the max and std exceeding 2^8 - 1? Please advise.

Thank you,
Muye

I assume you are using Q16 ImageMagick. When it reads images, it expands values to 16 bits, and shows those values.

Hi,

Thanks! Yes, I use IM 6.7.8 Q16. Though when I run

identify -verbose gray.jpg

,
I got the output in desired range:

Channel statistics:
Gray:
min: 0 (0)
max: 255 (1)
mean: 5.43318 (0.0213066)
standard deviation: 16.1351 (0.0632749)

Why's the output from the two commands different? Is there a way I can get mean = 5.43318 from "identify -format %[mean]"?

try

identify -format %[fx:255*mean]" yourimage

This worked, thanks a lot!

identify -format %[mean] gives 65535 on 8-bit gray image