RAW linearization

Submitted by Kemal on

Forums: 

Hi to all,

I would like to ask about the linearization step in RAW processing.
It is the first step in the process and I would like to learn how is it implemented?

Thanks a lot.

Dear Kemal,

Submitted by Iliah Borg on

Dear Kemal,

There are three disctinct linearization steps.

First one is applying tone decompression, and it is usually performed according to the compression table that is contained in the metadata that accompanies the raw file. Sometimes additional experiments are needed in order to determine what compression is in fact used, as the metadata is missing or not decyphered.

Second step (may be in the same table as the above) is lineraization of the extreme highlights. 

The third one is to compensate for the non-linearity in shadows caused by the flare. To perform this step a raw converter must usually rely on user-supplied calibration data, because this type of linearization is strongly dependent on the particular lens sample, and also on some minute details such as the dust in the chamber. In the consumer world, I do not know of any commercial converter that cares to perform this compensation.

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Best regards,
Iliah Borg

Thanks a lot Iliah,

Submitted by Kemal on

Thanks a lot Iliah,

There are some web sites giving limited info about the RAW processing. But, I could not find a book on this subject, explaining the process from A to Z completely.

If you have one, could you please advise me a reference book for learning the RAW processing from beginning to end?

By the way, RawDigger is really a great program ... congratulations and thanks for it.

Dear Karim,

Submitted by Iliah Borg on

Dear Karim,

Sorry but I do not know of any book that describes it. One of the problems is that such a book needs to go into the details of raw format, and be very specific about it. This may trigger legal actions. Ironically, under the copyright act we are allowed to reverse eng. the formats for the purpose of compatibility of the software we are writing - and we are not allowed to right books teaching others how to do it, or what are those formats, in full detail.

Good source of information about raw formats is software to read them - dcraw, RawSpeed, LibRaw, exiftool.

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Best regards,
Iliah Borg

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