When analysing an RGB colour image, I use a threshold (Image > Adjust > Threshold...) to set my desired gates for brightness, and choose 'Select' in order to select the thresholded pixels as a ROI. I can then simply use Analyse > Measure to gain measurements from the defined ROI.
However, when I split an RGB image by channel (Image > Colour > Split Channels) and attempt to threshold one of the resultant 8-bit images, the threshold dialogue does not provide me with the option to select the thresholded pixels as a ROI (only the options 'Auto', 'Apply', 'Reset' and 'Set' are now available, and not 'Select').
I've notice that converting the image type from 8-bit to RGB colour (Image > Type > RGB Colour) allows me to use the 'Select' option once more at the threshold dialogue, whilst keeping the image in grayscale and without appearing to change pixel intensity.
Is there a more logical manner to select thresholded pixels as a ROI in a 8-bit image? Or is the best option just the seemingly superfluous step of splitting channels followed by converting the 8-bit image to a RGB colour image?
Thank you!
You can use Edit > Selection > Create Selection to make an ROI that includes all the thresholded pixels.