Brightness: Brightening is done by adding a value “t” to every pixel value and darkening is done by subtracting a value “t” from a pixel value. Th result should be checked if is the range 0-255. Formula (1) calculates new brightness and (2) calculates new darkness value
 (1)
 (2)
 : pixel value of original image at position x, y.
 : new pixel value. Normalization: This method is used to place pixels near the middle colors of image. Difference between above method is that change is approached to middle color range (128 is pure gray).
 è  (3)
min: minimum pixel value in original image. max: maximum pixel value. ratio: how much the color separation is close to gray color(128). norm: Normalization factor given by the user.
Some examples for these two methods are shown in Figure 1. First method is simply brightens the image. Second method causes pixels to approach gray level (128) but if negative normalization factor is high, it approaches to 0.
(a)
 
(b) (c)  
(d) (e)  
(f) (g) Figure 1. (a) Original image baboon, (b) brightness by factor +50(norm) using first technique, (b) normalization by factor +50 using second technique, (c) brightness by factor +100 using first technique, (d) normalization by factor +100 using second technique, (f) brightness by factor -100 using first technique, (g) normalization by factor -100 using second technique.
C Source Code The source code can be found here.
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