A method for correcting the signal in an image comprising a dynamically changing signal and having a plurality of regions of interest, the method comprising the steps of: (a) providing an image having a plurality of regions of interest, these regions of interest each having a dynamically changing signal and areas between them; (b) determining a region of correction between at least two regions of interest; (c) calculating a correction signal from the region of correction; and (d) using the correction signal to correct a signal measurement from one or more regions of interest, characterized in that step (c) further comprises: (e) determining a reaction pixel count and a reaction pixel sum for each reaction region of interest; (f) determining an average pixel value for at least one region of correction for each reaction region of interest; (g) determining a background offset value for each average pixel value at a region of correction; (h) determining a pixel average and subtracting the background offset value from the pixel average to produce a region of correction difference value for each region of correction; (i) determining a correction signal by multiplying the region of correction difference value by the region of interest pixel count for each reaction region of interest; (j) determining a corrected reaction region of interest sum, by subtracting the correction value from the reaction region of interest pixel sum for each reaction region of interest. (a) providing an image having a plurality of regions of interest, these regions of interest each having a dynamically changing signal and areas between them; (b) determining a region of correction between at least two regions of interest; (c) calculating a correction signal from the region of correction; and (d) using the correction signal to correct a signal measurement from one or more regions of interest, characterized in that step (c) further comprises: (e) determining a reaction pixel count and a reaction pixel sum for each reaction region of interest; (f) determining an average pixel value for at least one region of correction for each reaction region of interest; (g) determining a background offset value for each average pixel value at a region of correction; (h) determining a pixel average and subtracting the background offset value from the pixel average to produce a region of correction difference value for each region of correction; (i) determining a correction signal by multiplying the region of correction difference value by the region of interest pixel count for each reaction region of interest; (j) determining a corrected reaction region of interest sum, by subtracting the correction value from the reaction region of interest pixel sum for each reaction region of interest. (e) determining a reaction pixel count and a reaction pixel sum for each reaction region of interest; (f) determining an average pixel value for at least one region of correction for each reaction region of interest; (g) determining a background offset value for each average pixel value at a region of correction; (h) determining a pixel average and subtracting the background offset value from the pixel average to produce a region of correction difference value for each region of correction; (i) determining a correction signal by multiplying the region of correction difference value by the region of interest pixel count for each reaction region of interest; (j) determining a corrected reaction region of interest sum, by subtracting the correction value from the reaction region of interest pixel sum for each reaction region of interest.