K7, K5 red color rendition issue? at iso 3200

Started May 4, 2011 | Discussions thread
Gerry Winterbourne
Veteran MemberPosts: 7,652
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Re: K7, K5 red color rendition issue? at iso 3200
In reply to aperture 56, May 5, 2011

aperture 56 wrote:

Guys, thank you a lot. Those are quite scientific explanations. Now, if i correctly got it - if the JPG file is already made inside the camera there is not much you can do about this issue in post processing, but you can do something by changing camera color and exposure settings before you make a file.

That's it exactly.

What is the story with a raw file then?

Ideally you want to avoid clipping (either highlights or individual channels) whatever you do. Shooting RAW does give you a bit of leeway, though. The DR of the sensor - whatever it happens to be - is captured in the RAW file but makers generally restrict the DR of the JPGs they derive from the RAW data to around 8 or 9 stops whatever the base file captured.

This means that some of the DR captured by the sensor is thrown away in the JPG conversion. What you see on the camera's LCD and on your computer when you open it is the JPG conversion done by the camera - this is true whatever mode you save to. If you save as RAW you can recover the DR that was thrown away - many people including DPR call this "highlight recovery" - which is, of course, one of the reasons to shhot RAW.

But a word of warning - the amount of recovery can be modest. Looking specifically at the K-5, on DxOMark at its base ISO of 100 its RAW DR is 13.7 stops but reading the chart on DPR it looks as if the Natural tone is about 8.7. That means about 5 stops are thrown away but a big share of that is in the shadows: my experience of converting K-5 DNG files is that at base ISO or just above there's about 1 stop of recovery or just a touch more.

Go to ISO3200 though and RAW DR drops to 9.3 stops so 8.7 stops in the JPG leaves only 0.6 stops for recovery. This will now be mainly in the highlights but even so 1/2 stop will be the best you can manage.

In other words, the advice to look at the RGB histogram and make sure the red channel isn't clipped is sound whether you shhot RAW or JPG. But if you do blow the reds then you've got a safety margin in RAW of about 1/2 stop at ISO3200 and about 1 stop at base ISO.
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Gerry

First camera 1953, first Pentax 1983, first DSLR 2006
http://www.pbase.com/gerrywinterbourne

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