Gordon, did you see this (in the other forum)?

Started 11 months ago | Discussions thread
GordonBGood
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Re: Gordon, did you see this (in the other forum)?
In reply to beholder3, 11 months ago

beholder3 wrote:

For those interested into these types of topics I recommend this long essay on how Canon manipulates raw data before the pre-cooked stuff is written into CR2 files:

http://www.stark-labs.com/craig/resources/Articles-&-Reviews/CanonLinearity.pdf

"Canon is rescaling your data before it hits the CR2 file. Based on the thermal signal both shifting your histogram left (likely based on stats from the optical black portion), it is changing and scaling the intensity (i.e., subtracting a constant from the whole image) the contrast or gain."

Thsi is not about manufacturers. They all do it.

Here Nikon:

http://forum.photozone.de/index.php?/topic/162-how-does-nikon-do-it/

Here Leica:

http://www.dxomark.com/index.php/Publications/DxOMark-Reviews/DxOMark-review-for-the-Leica-M9

This thread is not about lamenting any general raw manipulations that Pentax does for its raw output formats in its DSLR's such as compulsory Noise Reduction (NR) applied to the raw data at higher ISO sensitivities but rather the black level zero compensation that is a necessary part before raw conversion to view-able images, but for which it is preferred that full black level compensation be applied later rather than having black levels embedded in the recorded raw data as averaging to zero.  The K-5 series is the only model that has kept a positive black offset.

Yes, Canon save their CR2 raw files with a positive offset, which may be variable and which image signal may have variable gain tweaks applied to them as the first article to which you link states, but we Pentax users don'e care:  The Pentax K-5(s) models keep a positive black offset as we would prefer even though is offset may be variable for different ISO sensitivities and does not apply gain tweaks; the only problem we have with this is that the positive black level offset is not retained for higher ISO's (probably ISO 1600 and above) nor likely for raw images captured with Dark Frame Subtraction (DFS).

Yes, Nikon do even further manipulation for their NEF raw files made necessary my their option to save as virtually loss-less compressed files and also possibly some sort of sneaky NR to the dark tones, but having an available positive may be one of the reasons we prefer the K-5(s) models to their equivalent models from Nikon.

Yes, DxOMark has proven that Leica is using  a very slight compulsory raw NR for many of its ISO sensitivities, but why would we Pentax users care (or Leica users either for that matter considering it is so slight.  This is comparable to the compulsory raw NR applied by Pentax for the K-5(s) for ISO 3200 and above, and I don't even really care about that as it isn't really any more than one would likely apply anyway in post processing, and as it is applied to the raw data rather than to demosiaced raw data, it has less side effects on the resulting images.

In summary, yes, we know that raw data as saved into raw formats is rarely exactly as read from the sensor, but with the K-5 we have some modes where this data is very close to being "pure"; also, it seems that some tethering software may be capable of extracting the raw data at an earlier state in the processing pipeline where it is even more pure, at least as regards the black level offset.

Regards, GordonBGood

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