Magenta edge tinging at high ISO and a possible solution...

Started Aug 17, 2009 | Discussions thread
GordonBGood Veteran Member • Posts: 6,308
Re: PROGRESS: Version has one more tiny fix...

dlacoutu wrote:

Well, I gave v8.0 some more testing against my proof-of-concept method (slightly modified to better handle fine variations*), and I'm sorry to say that the ridge I mentioned before is corrected using the dumb method...

So, it seems to be present in the masked stripe (which is a good news for me!)...

BTW, your application gives a way better result maintaining WB, and in global contrast!

Modified proof-of-concept method:

  • reduced the black stripe to a one-pixel column (in several steps) to average it line by line (could not do it via ImageMagick in short notice, so went the dumb way)

  • resized it to the width of the pic.

  • added it above the original pic using "Difference"

  • applied it a gaussian blur to smooth the resulting banding in a satisfying manner (ended up with a radius of about 5.0)

Hey Dominique, that's good news that you can eliminate your ridge using your method, which seems similar to my own other than that you aren't averaging so much, although wouldn't you apply the Gaussian blur of the correction layer first before taking the difference? A couple of differences between your method and mine are as follows: 1) that you will actually subtract too much from the image and try to make some blacks "blacker than black" which is what increases the contrast artificially, and 2) that your method will include hot pixels in the border in the average where as I exclude them by using a percentage of the population.

I'm currently working on adding support for PEF format files, so will have a look at whether these differences explain the difference in results. It's easy enough to reduce my effective blur radius to see if that is it, but I am reluctant to throw away the tracking median level by population as that gives me a better "average" than an average that has a variable number of the negative going noise pixels clipped to zero.

Regards, GordonBGood

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