Scans of 1970s photos: black is dark purple
Posted: 2015-09-11T23:26:29-07:00
I have several image files, of 1970s photos taken several years apart and developed in different places, that all have the same problem.
Most colors in the photo—bright yellow, green, blue, pink—are fine or are only slightly off. No problem.
White (such as the white border of the photo) has turned into a pale yellow. That's only a minor problem; a histogram will fix that.
But what is supposed to be black or a very dark version of another color, has turned into dark purple.
For instance, a girl's blond hair is yellow when it's in bright light, but turns dark purple when it's in shadow.
So my questions are twofold:
1) How do I create a mask based on "How close is this pixel's color to dark purple?"
2) Once I've created an temp-image where dark-purple pixels are opaque and not-dark-purple pixels are transparent, what's the best way to de-purpleize the temp-image?
Particulars: ImageMagick 6.8.9-6 Q16 x64 2014-07-22 under Windows 7 64-bit.
Most colors in the photo—bright yellow, green, blue, pink—are fine or are only slightly off. No problem.
White (such as the white border of the photo) has turned into a pale yellow. That's only a minor problem; a histogram will fix that.
But what is supposed to be black or a very dark version of another color, has turned into dark purple.
For instance, a girl's blond hair is yellow when it's in bright light, but turns dark purple when it's in shadow.
So my questions are twofold:
1) How do I create a mask based on "How close is this pixel's color to dark purple?"
2) Once I've created an temp-image where dark-purple pixels are opaque and not-dark-purple pixels are transparent, what's the best way to de-purpleize the temp-image?
Particulars: ImageMagick 6.8.9-6 Q16 x64 2014-07-22 under Windows 7 64-bit.
