convert PhotoBoothXmas_0109.JPG -separate +append -define histogram:unique-colors=false histogram:hist6.png
![Image](http://www.fmwconcepts.com/misc_tests/histogram/hist6.png)
Your result from PS
![Image](http://www.fmwconcepts.com/misc_tests/histogram/RGB_Composite%20Histogram_Photoshop.png)
Prior to IM 6.8.5.0 you would need to add -set colorspace RGB before the -separate.
It is odd to me that this is not the same or equivalent to averaging the channels by
convert PhotoBoothXmas_0109.JPG -separate -evaluate-sequence mean -define histogram:unique-colors=false histogram:hist7.png
![Image](http://www.fmwconcepts.com/misc_tests/histogram/hist7.png)
which is the same as
convert PhotoBoothXmas_0109.JPG -colorspace OHTA -channel R -separate +channel -define histogram:unique-colors=false histogram:hist8.png
![Image](http://www.fmwconcepts.com/misc_tests/histogram/hist8.png)
Aside: In my redist script, the global histogram is one of many options that can be used.