Units for measuring average grey value?

I have measured the average grey values of JPEG images that have been converted to 16 bit greyscale, and now I am making graphs for a thesis. But I can’t figure out the units for the average grey value axis? Does it go from 0-255 where 0 is all black and 255 is white? If so, what should I name the units?

@Rubberduck

Welcome to the Forum - and best-of-luck with the thesis! :slight_smile: Always fun…

It would be great if you could post some of those original images - as well as the step-by-step protocol you used to get your data. Then we can better assist you - we are missing too many details at the moment to be of use.

But maybe - to get you started though… take a look at the histogram of your images (before/after conversion). That should give you some insight perhaps?

eta :slight_smile:


This is the type of image I have been working with, JPEG files with RGB color profile. I checked the histogram as suggested and they appear to be a 16 bit image due to the color intensity is being measured on a 0-255 scale, is this correct? So 0 is totally black and 255 is blinding white? If so I can just add 0-255 to graph axis labels.
Edit: I am still unsure about the units used by Imagej when measuring mean grey value from a color JPEG, and I have a deadline looming very near. If anyone could clear this up I would be very grateful.Would hate to use a graph with no labelled axis units.

Sorry dear,

but it is not our fault if your deadline is near and if you don’t respond to the advice of Ellen.

ImageJ converts RGB images to grey-value images that show 256 levels, i.e.—if you don’t process the converted images—there is little sense in converting them to 16bit grey-value. As Ellen has pointed out, you may inspect the histogram of your images:
After convertion, RGB images should show values between 0 (black) and 255 (white)—no?.

Spatial mean values will also be between 0 and 255 but in general no longer integer.

Does this help?

Herbie