16.4.5 Maximizing Contrast

There are a couple of obvious methods to maximize the effects of the flow field being visualized, in particular, to contract the blurring tendency from the the random noise texels being blended together. One simple method is to scale and bias the image to maximize its contrast. The imaging subset makes this easy. Process the image by doing a pixel copy, turning on sink after the minmax operation. With the minimum and maximum values obtained, you can execute glCopyPixels() again, setting scale and bias in the pixel pipeline to scale and bias the image.

Or you can do a full histogram equalization. Using the histogram feature, copy the image through the pixel pipeline, then process the resulting histogram to create a lookup table. The lookup table will balance the intensities into a linear ramp. Again use copypixels to remap the pixel intensity values. In detail:

1.

glEnableGL_MIN_MAX(GL_MIN_MAX)

2.

glMinmaxGL_MIN_MAX, GL_LUMINANCE, GL_TRUE(GL_MIN_MAX, GL_LUMINANCE, GL_TRUE)

3.

glCopyPixels() of LIC Image.

4.

glGetMinmax() to get minimum and maximum pixel values.

5.

Compute a scale and bias value to get full 0 to 1 dynamic range.

6.

glDisableGL_MIN_MAX(GL_MIN_MAX)

7.

glDisableGL_MIN_MAX(GL_MIN_MAX)

8.

glPixelTransfer() to set scale and bias value.

9.

glCopyPixels() of LIC Image to rescale it.