Contrast stretching

Since humans can distinguish many more colors than shades of gray, another useful contrast stretching technique is to map the gray levels into colors this technique is called pseudo-color enhancement. 

If we consider an 8-bit image, we have the lowest value of 0 and the maximum value of 255 these are the values to which we want to stretch the pixel intensity. In general we have and (0 and 255, respectively, in this example). After that, we have to scan all pixels in the image and compute the lowest and the highest assumed value of the pixel we call them V j and V j . In order to apply the contrast stretching operation, we apply the following formula to each pixel P, obtaining P ... 

Keywords— DWI, segmentation, thresholding. Gamma-law and contrast stretching. 

Standardize Image Background = 0.02 is used for this experiment. Fig. 4 shows image response of contrast stretching in which the original value r is mapped to output value s. 

Table 2 shows intensity of lesions on histogram thresholding. The threshold values are compared between Gamma-law transformation and contfast stretching. Minimum 0.48 and 0.28 are the optimal threshold value for the Ganuna-law transformation and contrast stretching respectively. 

Table 3 Performance evaluation for each lesion Comparison between Gamma-law transformation and contrast stretching algorithm...

Enhance- ment Technique Gamma- law Contrast Stretch Gamma- law Cc trast Str di Gamma- law Ccmtrast Stretch... 

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