How do I use a for loop to go through each pixel, and add on the brightness value? On MATLAB

Task 1 Brighten: individually modifies the RGB channels of an image, brightening or darkening it. Use Loops! function [ outImg ] = makeBright_L( inImg, brightness ) This function brightens each pixel and writes out the new image to outImg. The value of the input parameter brightness is the amount by which the image should be brightened, so it can be any real number in the range [-255 255]. Positive values will brighten the image, while negative values will darken the image. You must use loops to modify each individual pixel values.