I´m working in a project to get images from DDSM ( http://marathon.csee.usf.edu/Mammography/Database.html). I´ve got the step to convert (LJPEG to LJPEG.1) and now I´m with the step to convert LJPEG.1 to PNG, but the problem is the PNG image must be of 12 bits (because the original image of DDSM has 12 bits).
I know it´s not possible to obtain directly a 12 bit image from PNG, so I´ve used 2 ways:
With this two options, I get the same result, a matrix with max(I5(:)) = 4095, so the process is OK and I could see it in a figure, but the problem comes when I want to save in a png file, because the image must be saved in 16-bit and get me a dark image with a big size (four times the 8 bit png image). I also checked the value of bits: 13, 14, 15 and 16 and their values are 0.
I´ve used the PNG option of 'SignificantBits' with 12, but I obtained the same result.
Any ideas to solve the problem? I´ve found many articles about it but any of them gives a solution.
Thanks & Regards
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Do not downscale the data: it must be full-range for the bitdepth (16). Use 'SignificantBits' of 12.
Grayscale, 16 bits per channel, 12 significant bits, is the way that PNG represents 12-bit grayscale images. Decoders are allowed to ignore the 12 bit specification
See 18.104.22.168. sBIT Significant bits in http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html