identify command interpretation

[lionel]

Hi,

I tried the indentify command (with the verbose) and would like to know how to interpret the output.
More precisely I would like to know from the statistic and the histogram values if I can identify properly if this picture is under-exposed or over-exposed ?

Thanks.

[snibgo]

There are many ways to interpret the output. If these are ordinary photographs, the mean and standard deviation of each channel is useful. For a "correct" photograph, the mean will be around 0.5 and the SD will be around 0.17. This isn't a solid rule; a low-key photograph that contains mostly shadow will have a lower mean. A high-contrast subject will have a higher SD.

[lionel]

Thanks , it seems to be useful for my time-lapse camera, I would like to read this value after a snapshot to re-adjust my capture parameters.
What does the mean and deviation represent ? is there a definition somewhere.

Thanks

[fmw42]

The mean is the same as the average pixel value. For standard-deviation see https://en.wikipedia.org/wiki/Standard_deviation