算法：随机化亮度和对比度值，有约束

Question

I want to do a random brightness and contrast adjustment to an image, such that...

brightness = random in range (brightness_min, brightness_max)
contrast = random in range (contrast_min, contrast_max)   
outputImage = inputImage * contrast + brightness;

But when I do this, because the range of brightness and contrast values in my application are so large, I often output an image which is all white or all black.

I want an algorithm to choose a random brightness and contrast pair such that: no output is a solid color (unless already so), and: the output retains some specifiable amount of detail (this part is less important).

I don't know how to describe what I want in technical terms, nor begin constructing the solution. Any help is greatly appreciated. Thank you.

Answer 1

Assuming that brightness , inputImage , and outputImage are all on the same scale, I'd change the formula for outputImage to

outputImage = (inputImage - averageInputImage) * contrast + brightness;

where averageInputImage is the average (mean, median, whatever makes sense) of the inputImage values. Assuming positive contrast and an input image with detail, the output should have some detail, even if for high contrast it is alternately white and black.