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Offline RAW Compress (ZIP / DNG)

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Offline ArtDen

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Re: Offline RAW Compress (ZIP / DNG)
« Reply #10 on: 27 / January / 2008, 15:11:32 »
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One question:
Is the picture data in a DNG file (created by DNG4PS) still in the form of Bayer matrix data (RGBG, not RGB)?
Yes, DNG contains Bayer matrix data, not RGB

Re: Offline RAW Compress (ZIP / DNG)
« Reply #11 on: 27 / January / 2008, 15:58:13 »
I have asked, because there is indeed a Linear DNG file format, containing RGB image
data  (demosaiced raw image data).
I want to do the demosaicing with my RAW converter (Raw Therapee), so I have not
taken the risk of converting my files until now.

Is it save to convert to DNG?

Re: Offline RAW Compress (ZIP / DNG)
« Reply #12 on: 17 / July / 2008, 21:27:37 »
Im trying to implement a lossless compression using ZLIB, but the raw sensor data can be compressed only by 20%

Since the CHDK RAW is coded with 8 x 10 bits into 80 bits, I just wonder if the current compressor would consider the data to be more random than what they should be.
Just wonder if by splitting the data into 4 differents colors, the currents compressor would reach a better compression rate since there are more correlation within an image or even among the 4 colors.

We can then apply usual compression algorithms.

I heard that LZO is quite fast and portable. May worth giving it a try?

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Offline LjL

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Re: Offline RAW Compress (ZIP / DNG)
« Reply #13 on: 18 / July / 2008, 07:18:38 »
Lossless JPEG uses a predictive encoding that works by taking the pixel to the left and the one above the current one, and encoding the difference between those and the current one - roughly speaking. Then it Huffman-compresses the result.

It sounds like a simple approach and if it weren't moderately effective, I guess they wouldn't have used it for LJPEG...


 

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