How to photograph strongly coloured subjects?

[StewartR]

I'd be grateful if those with a bit more experience and/or ability can help me understand how to properly expose photographs of strongly coloured subjects. Such as flowers for example. Here's one.

http://StewartR.smugmug.com/photos/154356708-M.jpg

When I took the photo, I thought it was exposed reasonably well. I shot it using ISO 200, 1/125th at f/8, which is one-and-a-bit stops down from Sunny-16 and seemed reasonable given that it was a brightish but overcast day. I checked the histogram (NB my 350D only has a single histogram, not separate ones for each colour channel) and it seemed OK too.

But I had huge problems when I uploaded the photo to the PC. My RAW converter (Elements 5) has separate RGB histograms and it was clear that the red channel was way over to the right. I can't remember right now whether the red channel was hard-clipped or soft-clipped, but if that's important then I can check. Below I've attached a graphic showing the RGB histograms, reconstructed from the finished image.

How can I avoid this happening at the time I take the photo? (Do I need to avoid it?) I'm concerned that I have no ready way of estimating what the exposure looks like in any one channel. Furthermore it seems to me that drastically under-exposing the photo to bring the red channel down would make the background very dark, and potentially noisy.

If I can't avoid these sorts of issues, how should I handle them? I tried reducing the exposure in the RAW converter, but bringing the red channel down into the unclipped zone meant that the picture as a whole was very dark. I tried reducing the contrast, which also brought the red channel down a bit, but the results weren't very attractive. (I think this picture should be contrasty!) In the end I reduced the exposure a bit, reduced the contrast a bit, and left the red-channel highlights still somewhat clipped, and that's the image you see above. I'm not particularly happy with the result but I can't see how to do much better.

All insights, comments and suggestions welcome. Thanks for your help.

[Sathi]

I am having the exact same problem now working with some wedding pictutes. If I adjust exposure so the bride's dress isn't clipped (usually in the red channel first, why is that?) the rest of the picture becomes too dark. I would be interested to see if anyone has a good solution to this. What I have been doing so far is making multiple working copies with different exposure levels and then masking them together but this is a pain. Shadow/highlight sometimes works well but often it leaves the picture looking weird.

I thaught I was pretty careful to check the histogram for blown out blinking spots, but then when I got home I found much detail lost in the dress with no indication that it was happening at the time of the pic.

[René Damkot]

That would be soft clipping I'd say. Pretty good 'repairable' in the Raw converter if you shot Raw...

Have a read here: Click (http://www.luminous-landscape.com/tutorials/restore-clipped.shtml)

[StewartR]

Thanks René, that's an interesting read. The saturation mask technique seems a lot of work, but it will be interesting to give it a try.

I do shoot Raw, and I was aware that I could recover soft clipping in the Raw converter, but my problem was that I couldn't find a way to do it without excessively darkening or desaturating the image. The saturation mask technique is clearly something that has to be done after Raw conversion, so have you any suggestions as to how I should carry out the Raw converison in order to give me something decent to work on? Should I desaturate in the Raw conversion to avoid clipping, and then re-saturate using the saturation mask technique?

Any ideas as to how I can avoid the clipping in the first place?

[René Damkot]

Thanks René, that's an interesting read. The saturation mask technique seems a lot of work, but it will be interesting to give it a try.

You do it once, but you have to remember to click the 'record action' button first ;)

I do shoot Raw, and I was aware that I could recover soft clipping in the Raw converter, but my problem was that I couldn't find a way to do it without excessively darkening or desaturating the image. The saturation mask technique is clearly something that has to be done after Raw conversion, so have you any suggestions as to how I should carry out the Raw converison in order to give me something decent to work on? Should I desaturate in the Raw conversion to avoid clipping, and then re-saturate using the saturation mask technique?

You can do a few things:
1) Correct clipping in Raw converter, and bring up the image using curves in PS.
2) Correct clipping with the 'exposure' (and / or highlight' (or what's it called again in ACR for CS3?)) slider in ACR, adjust 'brightness' slider to get the image brighter
3) Develop the CR2 twice, and blend exposures (Click (http://www.thelightsrightstudio.com/videos/BlendedExposures.mov))
4) As this is Photoshop we are dealing with, ther will be at least ten more methods to deal with it...

Any ideas as to how I can avoid the clipping in the first place?
Underexpose ? :lol:

[StewartR]

Underexpose ? :lol:How much, O wise one? :D

[René Damkot]

5 stops should be enough :lol:

[StewartR]

Or I could do 6 or 8 stops to be safe.

Seriously though: My camera's histogram gives me no clue that the red channel is blown out, and if I were to under-expose by 2 or 3 (or 5 or 8, or...) stops I still wouldn't know. Obviously I still want to expose to the right as much as possible. For common strongly coloured subjects like flowers, is there any established rule-of-thumb that I can use?

[René Damkot]

Not that I know of...
This might be of a little help: Click (http://www.photonaturalist.com/chromazone/tutorial_2a.html).
Then again, it only gives you the 'gray' of the desaturated image, not the individual channels... You could make something like that easily enough in PS though: Take a multi colored image, and hit Cmd-1 (red channel), Cmd-2 (Green Channel); Cmd-3 (Blue channel). Should give you an idea of the channel values for the three colors...

Of course for static objects, bracketing is the easiest option. After a few times you'll get to know what your typical adjustments should be...

[tzalman]

Stewart - the following is a trick that I've used with some success in similar situations. It is based on the fact that the red channel is not really clipped in the RAW. It is, however, becoming clipped when the daylight white balance is applied to the RAW data because that requires a multiplication of all the red values by approximately x2. You can verify this by decreasing the WB temperature in your converter and watching what happens to the red predictive histogram. I do two conversions - one at "as shot" WB or whatever looks best and the second at around 3000 degrees. Conversion one has great color but clipped luminance data. Conversion two has terrible color but complete luminance data. My photo editor allows me to put the image into HSV space (Hue/Saturation/Value where V is luminance data). I extract H and S channels from Con. 1 and V from Con. 2 and recombine them. Works a charm. I should imagine the PS equivalent is to go into Lab space and take the a and b channels from one source and the L channel from the other.

I know you work with PSE 5, but I don't know if this can be done with it. If not, curse me and ignore this. If yes, try it and let me know how you get on.