background of an image to 0

I have a 2d image( from microscope of cells) and I am trying to quantify intensity of fluoroscence. However i did not take a background fluoro image and was wondering if there is any way to polyfit the image to bring the offset to 0.

[AAS]

There are multiple images- hence I need a way to compare between these images

[Luis J Gilarranz]

Depending on what the images represent you could normalize them (dividing all the values by the maximum fluorescence value recorded) and then apply the threshold I was mentioning. However, if you have a treatment that affect the maximum fluorescence values then you could not do this and you could not compare across treatments. It would help if you put more information.

Answer 1

[Luis J Gilarranz]

Testing different thresholds to see which one removes the background without removing any cell...

%Identify the pixels abobe the threshold 
Mask = Image>Threshold;
%Set the background to zero
NewImage = Image.*Mask;