Count the number of red pixels (or area)

[j.cardeira]

Dear all,

I'm new at Image J, so I'm sorry if this topic was discussed previously.
I have a problem which some of you might be able to help me with.

How can I easily count the number of red pixels within a selected ROI in a picture?
I will explain. I have simple pictures with red-pink-purplish areas against a whitish background (the contrast is huge). So I just want to select a ROI in each picture and ask Image J for the number of red pixels in that area against the total number of pixels. I suppose this is an easy task, but I'm not too familiar with Image J.

Thank you all,
João Cardeira da Silva

[Sam Lloyd]

select an area and press [M]. make sure under results>set measurements you have area ticked. This will give you a percentage of the area which is one colour.