问题
I run a website with thousands of user-contributed photos on it. What I'd like is a script to help me weed out poor photos from good photos. Obviously this isn't 100% possible, but it should be possible to determine if an image has no discernable focussed area? I think?
I did a bit of googling and couldn't find much on the subject.
I've written a very simple script that iterates over the pixels, and sums the difference in brightness between neighbouring pixels. This gives a high value for sharp contrasty images, and a low value for blurred/out of focus images. It's far from ideal though, as if there's a perfectly focussed small subject in the frame, and a nice bokeh background, it'll give a low value.
So I think what I want is a script that can determine if a part of an image is well-focussed, and if none is then to alert me?
Any bright ideas? Am I wasting my time?
I'd be interested in any code that can determine other sorts of "bad" photos too - too dark, too light, too flat, that sort of thing.
回答1:
Too dark and too light are easy - calculate a colour average as you iterate through every pixel.
For your focus issue, I think you're going to run into a lot of problems with this one. I would strongly recommend looking up kernel convolution, as I have a sinking feeling that you'll need it. This allows you to perform more complex operations on pixels based on neighbors - and is how most Photoshop filters are done!
Once you've got the maths background to do it, what I would do is to convert your image to an array of unique values (as opposed to RGB) representing brightness. From there, use an edge-finder kernel (Sobel operator should do the trick) and find the edges. Once that is done, iterate over again, mapping the bits with no edge, and calculate the largest square area without an edge from this. It is probably the least CPU-intensive solution, though not the most esoteric.
来源：https://stackoverflow.com/questions/13436038/gd-imagick-code-to-find-if-an-image-is-well-focussed-or-not