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millermixing

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paul miller
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Ok guys and gals, heres a funny little problem I seem to have encountered that doesn't make immediate sense and I was wondering if anyone would be so gracious as to enlighten me once more!

THE KIT: I have a canon 20d shooting with a canon 50mm 1.8 Mk11 lens. I used Elinchrom D lites, set the camera to 1/60th at f8 and shot in my lounge with no ambient light, which has cream/white walls.

THE PROBLEM: On a few occasions the detail in the shadow areas is really lacking...so much so you can see blocks of information (a tiny bit similar to the JPEG compression effect) where it looks like the sensor has struggled to cope with rendering a subtle shift in tones from light to dark. This has occurred on some high contrast facial lighting on the dark side of the face and also on a black t-shirt that my model was wearing.

I thought it might be a problem with the sensor capturing pure black so I shot a frame at f8 in my kitchen with no lights on at all. The result was perfect black with no blocks of varying color (I spot scanned the image in photoshop). This doesn't make sense.

Maybe I had some lens flare on the sensor at the same time as taking the exposure and this overloaded the sensor so it couldn't capture the subtle, graduated tones on a few of the pictures? What do you reckon?

Cheers

Paul Miller
 
How about posting an example shot for us to see?
 
I'd love to post an example stewart but unfortunately I cannot upload at the moment. I can send anyone an example via email if anyones interested?

Cheers

paul
 
Have you tried viewing on another monitor? Mine does funny things with some dark shades sometimes.
 
It's very difficult to comment without seeing the image.

Could you be over compressing the image, to get the maximum number of images on the card.

If so try using LARGE jpeg and see if that helps. You could also try shooting RAW. Photoshop CS will handle RAW files from your 20D, although you may have to update to the latest Camera RAW plug in for CS (It's a free update from Adobe) . CS2 and CS3 are fine with 20D files
 
Yup, if it looks like compression artifact and your using jpeg compression its more than likely it is compression artifacts... you really need to get a setup where its reproducible and then try out the differant Jpeg settings, but, IMO just ignore jpeg settings and stick to RAW, then if your still having issues we can start looking at other (weirder avenues).
 
Thanks guys. I am experiencing this problem on a RAW file though. I was advised from another forum that its because I'm underexposing to achieve a low key effect but what I need to do is expose properly (because the majority of the 4096 levels in a 12 bit image are towards the highlights on the scale) even if it means I don't have a low key image. Then when I take it into photoshop I can drop the levels without throwing information away and losing shadow detail (working in 16 Bit). Apparently as you start working with underexposed images on digital (whether a creative decision or otherwise), there are fewer levels at this end of the scale (is that logarithmic?) so the effects of posterisation can be seen...also the histogram should be spikey...Can anyone confirm?
 
millermixing said:
Thanks guys. I am experiencing this problem on a RAW file though. I was advised from another forum that its because I'm underexposing to achieve a low key effect but what I need to do is expose properly (because the majority of the 4096 levels in a 12 bit image are towards the highlights on the scale) even if it means I don't have a low key image. Then when I take it into photoshop I can drop the levels without throwing information away and losing shadow detail (working in 16 Bit). Apparently as you start working with underexposed images on digital (whether a creative decision or otherwise), there are fewer levels at this end of the scale (is that logarithmic?) so the effects of posterisation can be seen...also the histogram should be spikey...Can anyone confirm?
Click to expand...
I'd say the advice you've been given is pretty good. The technique is called "exposing to the right".

If you had a seriously underexposed image and you brought the levels up in Photoshop, that could cause some unevenness in the tonality. But again, we're all just guessing without being able to see the image. What's stopping you uploading it?
 
Hey Stewart. I've uploaded photo. The best bit to look at is probably the forehead near the hairline where the transition of light is more gradual. Its difficult to see when the server limits the size but if you can't make it out I can crop even tighter and resend?

Thanks

Paul
 
For those who are interested in this but can't be bothered to click on Paul's gallery link, here is his picture:

toneproblem.jpg


Paul, it would he helpful to know a bit more about how you took this and what you've done to it since. You said it was 1/60th at f/8, I think. What ISO setting? Is this "as shot" or have you adjusted it in Photoshop or whatever? In particular, have you increased the exposure since it came out of the camera?
 
Hey Stewart, Thanks for pasting the photo into the forum...not sure how you did that...have to work that one out! The image is completely untouched, except for the fact that I had to take it into photoshop, save it for the web as a jpeg and crop it. I shot is at ISO 100. I haven't increased the exposure post shoot or anything like that. I'm starting to wonder if I can get around the problem at all because its very difficult to keep my lighting within the dynamic range of the sensors ability to capture detail in the shadows whilst also not blowing out the highlights...and thinking logically about it...if I want a shadow across the one side of someones face, at some point the image will have to fade to black, possibly zone 0 or zone 1 on the ansel adams scale...if not on the face then on the black drape behind!

I used Canons Digital Photo Professional on a shoot the other day and set the highlight warning to 244 and the shadow warning to 8. It was easier to expose the image up to 244 where the highlight warning started coming on but then I still found some shadow warning right within the texture of the hair. The only way I could see around this was to flood more light within the hair from front on which of course destroyed the texture of the light and caused the 'already at the upper limit' highlight value to go over 244 and into warning. Do you think I am restricted by the very mathematics of my Canon 20Ds sensor? It seems to make it particularly tricky when photographing black and/or low key stuff...and its not as bad for high key, white stuff. Help please if you can.

Paul
 
Paul

Don't know if this helps.

Took a copy of your image ( Hope you don't mind) and dropped it into Photoshop. A quick look at the histogram, shows it's all left orientated. There is just no data in the shadows. At a rough guess it needs about another stop in exposure at least.

The highlight data I'm getting ( from the blond hair ) is at max around 190 in the red channel, less in the other 2. The dark eyes area is 1. All indicates that the image is underexposed. Well certainly from the jpeg conversion of the RAW file.

I don't know DPP that well. I tried it a few years ago and it wasn't that hot, so I switched to capture one and never tried it again.

I know you are trying to get a moody look, but if the exposure is all wrong then you just wont get enough information in the file to work with

I did a quick experiment in Photoshop. I used CS3 ability to treat jpegs as in the same way it treats RAW files.

I increased the exposure to get something like a reasonable image. The shadows were still solid as there is no data for PS to work with. Naturaly the blond hair went very light.

I opened the image as a 16 bit image, this stops you, as the the yanks would say, "Bruising the pixels". Applied a Softlight layer mask and simply burnt the hair in to approach the the original density.

You may find that simply adjusting levels with an image that has sufficient shadow information may help.

If you want to play with Capture One, you can go to the Phase One web site and download a trial version. It's valid for 15 days I think.

http://www.phaseone.com/Content/Software/LESoftware/ProductOverview.aspx

You might lie to try some other RAW converters as well

Hope these comments help...
 
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