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12-30-2012, 09:30 PM   #1
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Recovering highlight detail (darktable)

Hi - hoping for some help for a beginner at digital PP.

I have a number of photos of yellow wildflowers taken in full sun. I am struggling to recover detail in the flowers.

What I decided at the time was I would use Av with no exposure compensation, knowing that the highlights would be overexposed but hopefully recoverable since I was shooting RAW files. I figured this was better than underexposing the background since by my understanding these would be more difficult/impossible to recover.

But now, it doesn't seem to matter what I do, I can't get any contrast in parts of the flower petals.

Questions:

1) Is there a better strategy for exposure in these situations?

2) Is there a reliable way to find out whether the highlights have been clipped in the RAW file itself?

3) If they haven't, what's the best way to coax them out?

I'm using darktable. Re 2), the darktable histogram shows the output levels, not input, so it's hard to know what the raw histogram looks like and whether anything has been clipped. Re 3), I have tried in darktable reduce exposure until the highlights aren't clipped, and the fiddle with Black or with Levels to spread out those tones but still they stay muddy - suggesting maybe they are clipped in the raw file?

(Let me know what I can attach to help... RAW file is too big and everything else will be 8-bit AFAIK ?? )

12-30-2012, 09:47 PM   #2
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Have you tried the Shadows and Highlights module?

There is a good chance they are just gone, you can't bring back totally blown highlights.

Underexposing is always better than totally blowing highlights, you can bring up an underexposed area fairly easily, just with a little added noise that can be fixed later.
12-30-2012, 09:52 PM   #3
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QuoteOriginally posted by russell2pi Quote
What I decided at the time was I would use Av with no exposure compensation, knowing that the highlights would be overexposed but hopefully recoverable since I was shooting RAW files. I figured this was better than underexposing the background since by my understanding these would be more difficult/impossible to recover.
Exactly backwards, especially if you are using K-5 or one of the others with the same sensor where much shadow detail can be recovered. With negative film, you'd have the right idea. But with digital (or positive film like slides) blown highlights are gone forever...
12-30-2012, 10:28 PM   #4
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QuoteOriginally posted by vonBaloney Quote
Exactly backwards, especially if you are using K-5 or one of the others with the same sensor where much shadow detail can be recovered. With negative film, you'd have the right idea. But with digital (or positive film like slides) blown highlights are gone forever...
Oh right -! Thank you, a very useful thing to know. It's a K10D though - does the same apply? So - as a general rule, expose for the highlights?

Elliott - thanks, I have tried that now, but it's a bit too subtle. Again pointing to the fact they may be blown in the raw file ?

12-30-2012, 10:55 PM   #5
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QuoteOriginally posted by russell2pi Quote
Oh right -! Thank you, a very useful thing to know. It's a K10D though - does the same apply? So - as a general rule, expose for the highlights?

Elliott - thanks, I have tried that now, but it's a bit too subtle. Again pointing to the fact they may be blown in the raw file ?
With a K10D, you really just need to nail the exposure as there just isn't that much room for recovery on either side, but I would try to expose as much "to the right" (towards the highlights like you were doing) but just don't allow any clipping -- you're not getting it back. (If it is a static subject, take 2 or more bracketed shots and HDR them later.) On a K-5, you can exposure more to the left and it is fine. Learn to read the histogram to see where you are clipping, and use the over/underexposed warning system if desired. (I forget what that is called because I don't like it -- the thing where the areas with no detail blink in yellow and red.)
12-31-2012, 09:24 AM   #6
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I can't speak of Darktable specifically, but usually if you blow out part of an image, you can tell when watching the histogram as you provide some negative exposure adjustments. If you've completely blown out anything, the histogram on the peak on the right size will stop reducing in size and just start moving left. When reduced enough that peak will move left leaving a gap. Whereas if you have not blown anything out, the peak at the right should reduce in size until it is about zero with no gap.

Unfortunately, you also have to take into account that you can blow out specific color channels, too. I'm not sure how Darktable deals with that or whether you can see individual histograms for each channel.

I do remember with my K10d, that I often had blown highlights and had to expose for the scene. I often preferred having some blown highlights than underexposed area because the noise was quite significant on that camera. i.e. I picked and chose what was important. I also found it beneficial (since I shot exclusively raw) to set the contrast, in camera, as low as possible and use the resulting histogram as an indication of how much dynamic range I could capture with the RAW. I'm not sure that makes the most sense, but if I couldn't capture the whole dynamic range with the displayed JPG at the lowest contrast necessary, then I would need HDR or to choose what I was willing to sacrafice in terms of details (highlights or shadows).
12-31-2012, 10:03 AM   #7
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Better than doing an automated HDR, wich will look artificial, open the shots as layers in an image processor and do it manually...it'll look much better.
For your particular problem i think you're done...the dynamic range on that camera does not have enough headroom.
Only one solution i can think of: export your image to the GIMP, look for detail in some of the flowers and heal some detail from the flowers that have to those that do not.
Maybe you might want to try a more powerfull, less effects and more geared towards getting everything out of Raws than Darktable...i like it too but i've been reading a lot about PP software and you might want to try Photivo...it's powerfull, not very user friendly but it can handle Raw files really well.

12-31-2012, 12:29 PM   #8
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For next time: put your camera into spot meter mode and take your reading from the flower.
01-01-2013, 11:13 AM   #9
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I appreciate you use a different program, but this kind of highlight recovery is right 'up the alley' of our very own Pentax Digital Camera Utility software. It has an excellent 'Highlight Adjustment' tab which works on a very narrow band of clipped highlights - plus you have the added feature of sliders that control specifically whether you recover 'brightness' data or 'saturation' data in these extreme clipped areas.

In this case with the flowers you would be going for 'saturation' to restore the lost colours in the petals, and it can be very effective. This highlight tab will not interfere with the brightness levels of any other areas of the histogram apart from the very extreme right hand edge, so you won't have to make a lot of compensatory adjustments elsewhere.

I know that the Pentax Software has been difficult for many people to get started with, and that's why I wrote my Mini Guide, which I have heard has been helpful for people both here and on the UK forum. It gives details of this highlight correction feature so it may be useful for your issue here. Here is a link to the article : https://www.pentaxforums.com/forums/post-processing-articles/206286-pentax-di...ini-guide.html
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