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12-29-2007, 02:58 PM   #1
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More Skin Tone Burning Questions

I posted a while ago about some reds (on some bulbs being burned, or the red channels being clipped), this is what initially started by search for answers. First of all, I'm shooting with k10d, doesn't matter which lens (50mm/1.4, 18-55kit, 55-200) as the results are similar across all of them. Basically it seems that my camera is consistently clipping the red channel.

I'm using Apple Aperture 1.5.6. The photos below were taken with my 50mm 1.4, in P mode @ f/2.4, 1/15, 0ev, and ISO 400 and no flash.

I'm including the screen grab of the photo, with the hot areas hilighted, and not highligted, as well as the histogram. Is there something wrong with my camera or is this what happens with indoor lighting for everyone. Even though I shoot in RAW, I wouldn't think I'd have this much post-processing to do. Any insight?

-- edit --
Ovbiously, this is a most extreme case, but I'd say about 90% of my indoor photos exhibit this problem to varying degrees.
--/edit--








Last edited by mitchkramez; 12-29-2007 at 04:29 PM.
12-29-2007, 03:48 PM   #2
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I do a fair amount of indoor (tungsten or warm CF bulbs) shooting with a 50/1.4 + RAW (PEF) and I've never seen this sort of behavior from my K10D. I'm not a qualified expert, but my thought is that there is something fundamentally wrong with your K10D. By the way, what did you have the camera white balance set to? I know this is not an issue when you post-process the RAW file, but my RAW processor defaults to the camera setting until I tell it to do otherwise... but I don't know what Aperture does.
12-29-2007, 03:54 PM   #3
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MNCurt, These are with the WB set to the Tungsten lighting.
12-29-2007, 08:26 PM   #4
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Just looked at a couple more of my images - one of a Siamese cat on a red background, taken in Tungsten light with my 50mm f/1.4 lens... lots of red channel in the histogram, but no saturation/clipping. Did an auto-bracketing sequence and even the +1 stop image does not clip in the red channel.

12-29-2007, 08:45 PM   #5
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What type of metering were you using? Center, Weighted or Pattern? also, which focus mode are you using? Center or Select?
12-29-2007, 08:50 PM   #6
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I see this a lot too. I've learned to make sure to use EV compensation to, uh, compensate.
12-29-2007, 09:20 PM   #7
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There was a time this was called overexposure.
12-29-2007, 09:33 PM   #8
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You've got heavily red-biased light and a subject with reddish tones that fall into the overlap between the red and green channels. Welcome to the fun of trying to get decent skin tones from caucasians under tungsten light.

The biggest weakness of the Bayer filter sensor is caucasian skin tones, because they often fall into the overlap in sensitivity between the green and red sensor sites, causing odd colour shifts. This is why no digital can match the skin tones of Portra without serious profiling work and post-processing.

To some extent this will happen to everyone under tungsten light, although underexposing a bit will prevent saturating the red channel.

12-29-2007, 09:43 PM   #9
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mawz, so you wouldn't say there is anything inherintly wrong with the camera? second if i'm under exposing, will i be able to gain most of that "brightness" back in post processing?
12-29-2007, 09:54 PM   #10
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Mitch - using 'matrix', center focus, single; here's a sample with histogram:
Attached Images
 
12-29-2007, 09:55 PM   #11
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QuoteOriginally posted by mitchkramez Quote
mawz, so you wouldn't say there is anything inherintly wrong with the camera? second if i'm under exposing, will i be able to gain most of that "brightness" back in post processing?
Are you using the "bright" vs "natural" tone setting? If so, try turning it off.
12-30-2007, 03:06 AM   #12
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Mitch, as I tried to say in your previous thread relating to this, you haven't discovered anything new. The problem you describe is as old as photography itself. Every medium, including film, digital sensors, and even our own eyes, has a limit on the dynamic range it can record. When that limit is exceeded in either highlights or shadows, image detail is lost or degraded. In the case of digital, this can be across the board or on any single color channel (the red channel is particularily troublesome, for example). And you can expect this often since the world around us is seldom lit with flat low-contrast lighting comfortably within the range of whatever recording medium. Instead, lighting obviously varies greatly in both intensity and contrast. Therefore, your only solutions are to either live with the results (not unreasonable since we do it all the time in relation to our own eyes), attempt to modify the scene to lower contrast (adding or reducing light), or try to fix it afterwards with software techniques as described in the previous thread.

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12-30-2007, 09:09 AM   #13
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Canada_Rockies - I don't think the Bright vs Natural applies when shooting Raw, I could be wrong though.

Stewart - Thanks, I should have posted these photos in my previous thread, but I just had this nagging feeling that I was doing something wrong. Anyways, sorry for kind of that double post. Here's to under exposing in Tungsten light!

Thanks again everyone. I think my fears have been put to rest.
12-30-2007, 10:13 PM   #14
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mitch, the question has been answered well as I see you know. I won't address that directly. What I want to address is the program you are using and what is configured as a "blown highlight". It's way way too liberal in what it is saying it blown/clipped. Take the table surface as an example. There's -plenty- of detail there. However when you turn the blown highlighting display on, the whole surface is marked as blown/clipped, even the section of the surface in shadow of that bottle. [!] how can that be? That's just not right. Import that picture into a trial copy of Adobe Lightroom, hit 'j' to turn on clipping, and I guarantee you it will give you a very different, and accurate, display of what's clipped.
12-31-2007, 10:11 AM   #15
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I also encountered the same problem, mostly. I shot in RAW and mostly the skin is reddish.
To simply fix it, I use Silkypix Developer Studio 3.0E.
Before (after WB and Exp bias are set):



After (more accurate):



What i did is:



In WB Adjustment, Hue value should be between -90 till -150
i always set saturation: 0.20.

And if still reddish, i mostly add this setting:



Mostly, i add these 2 setting on all pics i taken. The final result is skin color is more accurate. But it's me.
Silkypix does have lot of hidden capabilities.

kyrios
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