Enhancement |
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Contrast: When increasing contrast, pixels that are darker than 127 (pixel's value) are made darker and pixels that are lighter than 127 are made lighter. This works fine when the values in the histogram is distributed around the middle; otherwise, contrast will not have the desired effect.
Luminosity: Increasing or decreasing the luminosity shifts the histogram.
Gamma: Moving the slider to the right (greater than one) will increase the number of dark values and darken the image; moving to the left (less than one) will increase the number of light values, lightening the image. The mapping function is an exponential curve.
Automatic levels (histogram normalization) stretch an image's pixel values to cover the entire pixel value range (0-255).
This operation attempts to flatten the image histogram. Histogram equalization employs a non-linear mapping which re-assigns the intensity values of pixels in the input image so that the output image contains a uniform distribution of intensities.
This operation attempts to make uniform the background illumination when, for instance, an image has been acquired by a microscope with a nonuniform illumination. There are two ways to correct this issue:
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