accelerate

问题 I am using Swift and Accelerate and am trying to color-correct an image using the vImageContrastStretch method available in Accelerate's vImage module. When I try to stretch the histograms I get a result which does do exactly what I want, but it is a bit too relaxed. The resulting image histograms still have unwanted space on the sides. As you can see in the image, the result of the vImageContrastStretch (middle) operation still has some room for snipping on both sides of the histogram

问题 In a problem I'm working on now, I compute some values in a matrix x and I then for each element in x need to find the index of the closest element below in a monotonically increasing vector X as well as the relative proximity of the x elements to the first elements on their either side. (This is essentially linear interpolation without doing the actual interpolation.) I'm doing this maaaany times so I really super extra interested in it being as fast as possible. I have written a function