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07-28-2009, 01:16 AM - 1 Like   #1
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Finally, an in-camera Raw Histogram!

Hello,

All the RAW aficionados around here must have run into the same problem: how to know when your RAW RGB channels really clip, as the histogram displayed is based on the preview JPG and thus doesn't really show what is in the RAW file.
Anyone tried to properly expose a Tungsten scene? You always end up with at least 1Ev underexposure, due to the seemingly clipping Red channel on your camera: once you get into your PP software, it magically transforms into a one-stop highlight headroom, so you're forced to push the exposure and noise really starts to creep in.

I personally find that getting satisfactory JPG previews right out of the camera is pretty useless for the RAW shooter (as every photo I make goes through ACR), and I'd rather like to have an accurate histogram.

So yesterday, browsing the web, I stumbled upon this little utility : Rawnalyze. It can display a real RAW histogram, without any interpretation, along with individual RAW channels clipping...

So, I started experimenting with WB and contrast/saturation controls, until I had something vaguely similar between my K20 and Rawnalyze...

I finally found a quite satisfactory setting where highlights clipping where pretty well rendered. Shadow clipping was somewhat less realistic, but it's less important for me (and anyway it was still waaaaay better than what I had before).

So, here are the settings:
- WB set to 4200K, Green+7
- Saturation -4 (slider all the way to the left!)
- Contrast -4 (slider all the way to the left!)

(note: it could still be tweaked a little bit, I only spent one hour on it)

Okay, you end up with really flat-looking, washed out green-tinted in-camera previews... Shooting indoors with Tungsten leave you with heavily orange-tinted previews too, as with magenta fluorescents and blue shades...
BUT the histogram is now a pretty close rendition of what you really have in your RAW file... It improved my Tungsten-lighted pictures in huge ways, as I can now obtain the perfect exposure each time.
Flash and Daylight were pretty spot-on too, fluorescent and shade lightings will be tested tonight.

ETTR now takes its full measure. When a channel is showing minute traces of clipping, ACR concurs at its default settings, but a slight exposure decrease (-0.05 to -0.1) removes all traces of clipping in a pleasant way (by pleasant I mean that there was no sense of lost colors).

Only missing thing is that an individual channel clipping does not blink in the camera preview. Blinks only show a full RGB clipping.

I'll try to add some media tonight or tomorrow...

07-28-2009, 04:32 AM   #2
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You must have been using K20D DNG files. It won't process K20D PEF!

David
07-28-2009, 04:57 AM   #3
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Yep, I forgot to mention this point...

Anyway, you don't really need it to check this out... Just set these values in your K20, snap happily, and compare with ACR results.

These values still need some refinements, but they are a really better alternative to the dopey histogram we are used to...
07-28-2009, 05:41 AM   #4
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good work

10char

07-28-2009, 07:54 AM   #5
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Okay, we learn something every day of our lives : I've just found out that this is called UniWB, and is already discussed in depth on the web...
07-28-2009, 01:38 PM   #6
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Awesome, yet another great thread by dlacouture (the other being the noise reduction one). Looks like I'll be giving this a shot. It's mostly an issue with high ISO tungsten situations, where I end up underexposing and get bad chroma noise when the WB is adjusted.
07-28-2009, 01:48 PM   #7
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I'm guessing you should take a shot of a white balance card to get the most accurate WB in post?
07-28-2009, 04:50 PM   #8
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A few pointers.

Sounds like a good deal of work has been done and I do not mean to discount it in any way.

However there are two main factors scewing the in camera histogram.

Applied WB and the tone curve or contrast curve.
These should be isolated and solved one by one.

I am unfamiliar with the RAW converter mentioned but use DCRaw in stead.
It allows you to get the channel push coefficients before WB is applied.

considering that the K-7 has a uniWB or native WB value of 5205 kelvin, then it does sound like you are a fair bit off.
A quick way to find the uniWB or native WB, which may work for you is to focus the lens at infinity move close to a wall and make sure you overexpose every single pixel and the use this image to set a custom WB.

It works on the K-7 and not on the K-m, so there is a chance, grab a test image and run it through DCRaw and check the WB coefficients.

That gives you a stonesure starting point in terms of WB and leaves only the work on the contrast curve.

Hope this helps.

07-28-2009, 10:33 PM   #9
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Duplo : that's exactly what I tried yesterday (overexpose a customWB), and it works on the K20... I end up with a 1,1,1 "as shot" color balance in PhotoME...

But I still have to set saturation and contrast to -4 to obtain a realistic histogram.

Krypticide : well, the Adobe WB presets still work, so they are a good starting point...
I'd say that if you were used to set your WB "by eye", it won't change much.

Last edited by dlacouture; 07-28-2009 at 10:59 PM.
07-30-2009, 03:22 AM   #10
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Well, after some tries, I found that the following settings are better :
- Saturation: -3
- Contrast: -2 (but not really important, so you can use anything from -4 to 0)

This, combined with the ETTR method, can lead to really clean 6400 shots...
07-30-2009, 03:25 PM   #11
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So now you set the white balance using the overexpose method, then set Natural with the -3 Saturation setting?

Also, once you do this, you can't overexpose any of the histogram at all (assuming you don't want to overexpose intentionally)?
07-30-2009, 03:30 PM   #12
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QuoteOriginally posted by krypticide Quote

Also, once you do this, you can't overexpose any of the histogram at all (assuming you don't want to overexpose intentionally)?
isnt that the whole point of having an on-the-fly histogram?

rather than telling yourself "well, when i get home, i might recove this blow out"
07-31-2009, 01:09 AM   #13
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Well, the metering will still behave exactly like before. WB is not used by the metering system...

but now, you know exactly what your RAW contains...
07-31-2009, 03:32 AM   #14
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QuoteOriginally posted by Gooshin Quote
isnt that the whole point of having an on-the-fly histogram?

rather than telling yourself "well, when i get home, i might recove this blow out"
That is one point, the other is optimal exposure for RAW processing and occational use of colour correction filtering which takes it a step further.

QuoteOriginally posted by dlacouture Quote
Well, the metering will still behave exactly like before. WB is not used by the metering system...

but now, you know exactly what your RAW contains...
Yep.

I am having a slight issue with the histograms and the WB value mentioned above by me are incorrect, not sure what went wrong.

So still a lot of work to do.
07-31-2009, 02:28 PM   #15
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QuoteOriginally posted by Duplo Quote
That is one point, the other is optimal exposure for RAW processing and occational use of colour correction filtering which takes it a step further.


Yep.

I am having a slight issue with the histograms and the WB value mentioned above by me are incorrect, not sure what went wrong.

So still a lot of work to do.
Got it. I guess I'm so used to having a bit of leeway on the histogram that it almost seems counterintuitive to not blow out any part of it at all anymore.
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