Strange phenomenon when pulling down the exposure in RAW

bomberman

bomberman

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I shot some BMXers. After i cleaned up the mess i got my camera out and took a picture of some against a fairly brights sky. there is some detail in the sky but i was shooting 2/3 stop over so wanted to pull down the sky in RAW, but to my horror when i do so the bright patches in the sky turn pink! I've done this trick before with overexposed skies but never had this problem. I have recently gone from a 400d to a 40d and wondered if it's got anything to do with it... although i can't see why it would TBH.

Has anyone else had this or know what causes it? is there a fix?
 
jobe said:
What program are you using, sounds like you have the Highlight Clipping Warning selected.

Wayne
Click to expand...

It does - in Photoshop/Elements look at the little triangles at the top of the RAW control panel.
Clicking on them them turns the warnings on or off.
 
Are you using Lightroom 1.x? I think that was a fault with early versions. It's a long time since I shot with my 40D but I do not remember seeing that problem with other cameras when pushing ETTR a bit too far.

Here's an overexposed example from my 40D, pulled back 1 stop in LR3. There is no hint of a magenta tone in the recovered areas, and if there was, with the tint set to +10 at the moment there is room to balance away from magenta to a little greener.

20100812_214122_.JPG
 
Thanks for the suggestions, i'm using UFraw in tandem with the Gimp. I've been using it for almost a year and not had any problems until now, can't figure out what's going wrong :thinking:
 
The bright areas are almost certainly clipped in one or more channels in the original RAW file - the colour information in those areas is consequently incomplete.

When you're knocking down the exposure, the software can relatively easily calculate a tonal (greyscale) value for the area, but has to make a guess about what the colour value should be for those pixels, based on the neighbouring pixels.

UFRaw is a graphic front-end the Dave Coffin's open source dcraw engine to decode the RAW files.

Scroll down to the section on HIGHLIGHT MODES on this page, which discusses some of the more technical details of using dcraw directly from the command line. It also explains in detail why you're seeing it.

Figure 7 in that section illustrates exactly the phenomenon you're seeing.

It's worth noting from the above, that the particular WB point chosen may have an effect on whether this phenomenon makes itself visible or not.

As tdodd mentioned, the early versions of Lightroom exhibited the same behaviour. Subsequent versions Adobe Camera RAW (the RAW engine for Lightroom) tend to flatten the colour information any areas that are overexposed in one channel to grey, which often works well for skies, but may not for other subjects. It becomes a trade-off.

I'm afraid the short answer is don't clip your highlights :)
 
WOW that's right on the money thanks. Figure 7 is exactly what it looks like, but i don't really understand the text.. So do you think it's to to with the WB settings on the 40d, compared to the 400d? as pulling down RAW files on the 400d gave me no such problem.

I might have to experiment with overexposing at various WB settings to see if i get the same problem.

one thing that does puzzle me is that when i hit the refresh button in UFRaw to bring all the wb settings back to default, it defaults to manual WB and is very VERY pink. The whole image. I've never seen it before. I wonder if i might have messed something up somewhere? The exif says i was shooting in Auto WB. I set a custom WB with welding glass the other week, but that shouldn't affect the camera's auto WB surely?

what's annoying is that even at 0EV, compared to the JPEG images, i can see bits of pink in the sky, so the RAW files of the whole shoot are now useless :(
 
It's possible that it's specific to the dcraw profile for the 40D or that there's some other condition that's caused it. Maybe you're just normally more careful about your exposures and don't blow them quite as much?

Try converting then with Canon DPP instead. It's free as you should already have it.
 
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bomberman said:
WOW that's right on the money thanks. Figure 7 is exactly what it looks like, but i don't really understand the text.. So do you think it's to to with the WB settings on the 40d, compared to the 400d? as pulling down RAW files on the 400d gave me no such problem.

I might have to experiment with overexposing at various WB settings to see if i get the same problem.

one thing that does puzzle me is that when i hit the refresh button in UFRaw to bring all the wb settings back to default, it defaults to manual WB and is very VERY pink. The whole image. I've never seen it before. I wonder if i might have messed something up somewhere? The exif says i was shooting in Auto WB. I set a custom WB with welding glass the other week, but that shouldn't affect the camera's auto WB surely?

what's annoying is that even at 0EV, compared to the JPEG images, i can see bits of pink in the sky, so the RAW files of the whole shoot are now useless :(
Click to expand...

Why not open it in DPP
 
Why not open it in DPP
Click to expand...

My computer's so slow that i'm scared to install it :lol:

Could it be something to do with the 40d having 14bit raw files as opposed to the 400d's 12 bit files?
 
As I mentioned earlier, it may be a combination of the profile and algorithms that dcraw uses and possibly the specific White Balance you've chosen.

Have you seen similar in other shots with overexposed areas?

Oh, and unless you're desperately short on disk space, install DPP.

If you are that desperately short on disk space, then don't take any more photographs as having them on disk will slow things down more.
 
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If you are that desperately short on disk space, then don't take any more photographs as having them on disk will slow things down more
Click to expand...

I hear ya. Am considering a new PC but i'll give DPP a go.

I have noticed pink highlights in a couple of the other shots i've looked at but others from the same shoot with the same sky in the background are fine. I've also noticed that some shots look flat in raw compared to the jpegs but i do have sharpness, contrast and saturation set to +1 in camera so i'm guessing this is probably an effect of those settings.

I'm going to install DPP in the next few days and i'll let you know if it makes a difference, if not i'll start experimenting with WB settings.
 
bomberman said:
I've also noticed that some shots look flat in raw compared to the jpegs but i do have sharpness, contrast and saturation set to +1 in camera so i'm guessing this is probably an effect of those settings
Click to expand...

Fairly normal. The in-camera processing is almost always going to give the tone curve a kick unless you set the Picture Style to 'Neutral'. Even then it may do.
 
Just to let you know that DPP is up and running and working well, and that there's no pink hue when adjusting raw files. Now that i've used it for a couple of days i actually prefer it to UFRaw - quicker, cleaner, more features. Thanks for the tip :thumbs:
 
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