Convert large 48bit TIFFs to JPEG2000

[Remigius]

Next experiment: I have downloaded the kakadu software. I remember to have found this site already last night, but due to the confusing number or options of the compression program I left it aside first. Now I have tried to compress my test image with default parameters resulting in a file of 1/10 the original size with preservation of the 48 bit colors. Comparison to the original again resulted in no visible differences and a blank difference image. So this looks really promising. Getting the size down a bit more might be helpful, but even with default parameters the results are quite acceptable to me.

Thanks again and best regards, Remigius.

[Remigius]

Experiments with -rate parameter: I have performed a few compressions with varying -rate parameter (2.0, 1.0, 0.5 and 0,25). The rate parameter sets the "bit rate", which is the number of bits per pixel of the original image. So a rate of 1.0 for a 48 bit image corresponds to a compression of 1:48. My impressions were as follows:

default setting: compression of 1:10, no visible differences to the original

-rate 2.0: compression of 1:24, no visible differences to the original

-rate 1.0: compression of 1:48, no visible differences to the original

-rate 0.5: compression of 1:96, slight artifacts become visible (in the sky), compressed image seems slightly softer than original, difference image blank

-rate 0.25: compression of 1:192, artifacts clearly visible in the sky, but not in other parts (stones of a wall), image seems softer than original, difference image has a few regions with a slight veil.

This is far from a scientific experiment, but hopefully useful for some of you...

Best regards, Remigius.

[schngrg]

To do a completely pixel lossless compression use the 'Creversible=yes' parameter, without any rate parameter.

kdu_compress -i infile -o outfile Creversible=yes


You can specify a rate of choice with 'Creversible=yes' also, although that won't serve any practical purpose.

And for lossy, specifying even a very high rate can still give some extra loss, to specify complete-codestream-retention in lossy mode, use: '-rate -'