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Author Topic: A7r and ETTR  (Read 11556 times)

digitaldog

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Re: A7r and ETTR
« Reply #20 on: February 05, 2014, 03:37:29 pm »

- To the other issues. I presume that any twisting of profiles is done after decompression of data and that the data is contanimated by noise, is that correct?

- Personally, I don't use a light meter just the histogram, aiming to avoid clipping on non specular highlights (*).

The way I build profiles is to make an ETTR shot of a CC-card, check for clipping RawDigger and use DNG Profile Editor. It seems to work for me. Anything wrong with that approach?

1. Correct (certainly with Adobe raw processors).
2. Which Histogram? They lie big time on the camera if you're shooting raw.
3. If you over expose the CC-card, the Passport software will tell you it can't build the profile. I'm not sure it's necessary to apply ETTR to the target anyway but if you're not clipping, you're fine.
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ErikKaffehr

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Re: A7r and ETTR
« Reply #21 on: February 05, 2014, 03:55:57 pm »

Hi,

I check my raw histograms using RawDigger, which I feel gives a good representation of the real histogram. That is done in post.

With ETTR I mean maximum exposure not clipping non specular highlights. Something like attachement, having very little clipping in sky.

Anyway, I have been shooting with Sony cameras for something like seven years and I have not observed any posterisation issues, except on shots including the sun. That doesn't say that issues don't exists, just that I have not observed it.

But I seriously doubt that the compressed tone scale used by Sony has visible artefacts as I think that the effects of compression are significantly less than shot noise. Very clearly, I don't think that having a non linear coding is a good thing, but I suggest it may not be a bad thing either.

I have not studied it in detail. I guess the best way to check it is to write code to compress the data with Sony's algorithms and decompress it using the same algorithm and subtract from the original data. I might test it, but it takes some time to write the code.

Best regards
Erik

1. Correct (certainly with Adobe raw processors).
2. Which Histogram? They lie big time on the camera if you're shooting raw.
3. If you over expose the CC-card, the Passport software will tell you it can't build the profile. I'm not sure it's necessary to apply ETTR to the target anyway but if you're not clipping, you're fine.
« Last Edit: February 05, 2014, 04:05:19 pm by ErikKaffehr »
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Vladimirovich

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Re: A7r and ETTR
« Reply #22 on: February 05, 2014, 06:45:55 pm »

The way I build profiles is to make an ETTR shot of a CC-card, check for clipping RawDigger and use DNG Profile Editor. It seems to work for me. Anything wrong with that approach?

Eric Chan directly advised (I have so many quotes that I had to google for couple of minutes inside my collection ) = http://www.luminous-landscape.com/forum/index.php?topic=70762.msg561908#msg561908

Quote
The DNG PE needs to be somewhat conservative in its chart wizard with regards to clipping because color tables are always applied after white balance.  Your raw capture may not have clipped data in its native coordinate system (native RGB, without WB applied), but that data can become clipped after WB is applied.  That leads to problems with the color mapping.  DNG PE will generally detect this case and prevent you from proceeding.

My recommendation is simply to bracket exposures and then pick the brightest one that DNG PE will accept without giving you an error.
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Iliah

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Re: A7r and ETTR
« Reply #23 on: February 05, 2014, 09:14:28 pm »

From my tests the white patch on CC24 needs to be at least 1/6 EV below clipping. 1/3 EV past clipping usually results in more stable profiles.
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