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Archive 2012 · 5dmk2, problems with pure reds (and sometimes blues)
  
 
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p.1 #1 · p.1 #1 · 5dmk2, problems with pure reds (and sometimes blues)


I have a problem in some of my photos, most commonly with the clothing that people wear that is mono-color, like a cap or dress that is pure red or a skirt that is a pure blue in color.

I'm not sure exactly how to describe this -- but sometimes I find that if the object is even slightly covered by shadow, the 'tonal depth(?)' is poor, or the jump from one luminance level to the next is very visible. Things end up looking like 'mush', and it shows even when viewed on a computer monitor (32-bit color) and/or resized at much lower resolution for online viewing.

I'm always shooting raw, most of the time I use DPP to convert but occasionally I use Photoshop elements 10. One of the things mentioned online is "Highlight Tone Priority", I've got that in 'My Menu' for quick access and turning that off can sometimes alleviate that problem. But I've checked my photos from this last weekend and other times, even with that off I still get this problem sometimes. Anything else I should be trying? I'm always using expose-to-the-right and sometimes I have this problem even if I'm pulling the exposure back by half a stop or so.

It only happens, or it's only noticeable when it happens with mono-color. I've never seen it happen on my 5d2 for colors like orange, pink, turquoise, yellow, white, etc. And I've never seen it with green either. ISO 100~200, f/1.8~f/2.8, and reasonable daytime shutter speeds like between 1/2000 and 1/400.



Feb 02, 2012 at 09:05 PM
mpmendenhall
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p.1 #2 · p.1 #2 · 5dmk2, problems with pure reds (and sometimes blues)


This might be color channel clipping, where the brightness in one color channel exceeds the dynamic range of the camera, though the camera still shows "correct" exposure since the total brightness from all colors combined (what the exposure sensors use) is still within range. I've found red channel clipping to be rather common with my camera body (5D) too; for images where I want to preserve detail in saturated reds, I will often "underexpose" by at least one stop from what the camera recommends.

Posting an image where you see this problem might help further diagnosis.



Feb 02, 2012 at 09:12 PM
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p.1 #3 · p.1 #3 · 5dmk2, problems with pure reds (and sometimes blues)


Ok I can certainly do that when I get home in several hours.
I don't think it's channel clipping, I've seen that before when indoors under heavy incandescent or decorative lighting (2700-3500K) where the reds are overblown if you're not careful, the blues are underexposed. I always have the histogram on RGB and this was outdoors with rather typical daytime light.



Feb 02, 2012 at 09:27 PM
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p.1 #4 · p.1 #4 · 5dmk2, problems with pure reds (and sometimes blues)


Unfortunately, the RGB histogram is not a reliable indicator of actual channel values. The histogram is generated, I think, from the image after it has been processed/interpolated by the camera, combining information from all the color channels to estimate the brightness at each point. Even when the red channel is solidly clipped, the camera may vary the red level in the preview image (and histogram) based on what the other color channels are doing, making the red histogram appear to have a reasonable spread of values when a "true" histogram of the RAW data would show a narrow clipping peak at the maximum value.


Feb 02, 2012 at 09:33 PM
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p.1 #5 · p.1 #5 · 5dmk2, problems with pure reds (and sometimes blues)


Access wrote:
I have a problem in some of my photos, most commonly with the clothing that people wear that is mono-color, like a cap or dress that is pure red or a skirt that is a pure blue in color.

I'm not sure exactly how to describe this -- but sometimes I find that if the object is even slightly covered by shadow, the 'tonal depth(?)' is poor, or the jump from one luminance level to the next is very visible. Things end up looking like 'mush', and it shows even when viewed on a computer monitor (32-bit color) and/or resized at
...Show more

hard to say, some possibilites:

1. if you don't have a wide gamut monitor, the monitor may be clipping everything (or even if you do and you are working in sRGB mode); you should see a red rose on wide gamut monitor in prophotorgb 16bit working space compared to red rose in sRGB, either lots of mush on the latter or it has to gamut map things down and it retains detail but loses the proper shade and the saturation totally

2. sometimes it seems the 5D2 does have poor color distinguishing abilities in rich dark tones, just a vague impression i get

3. red may be clipped in even the RAW file itself

4. turning off HTP would think it would make it worse but if it makes it better maybe it's more shadow mush and points more to #2? although i would've thought #1 more of the problem than #2



Feb 02, 2012 at 10:29 PM
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p.1 #6 · p.1 #6 · 5dmk2, problems with pure reds (and sometimes blues)


I thought about the monitor, I checked this morning and it's the standard 32-bit color.
At least the gamma is set correctly. I can typically shift the object throughout the whole level (ie. from bright red to dark red) and it looks the same either way.

I don't think it's the monitor because sometimes a similar photo of nearly the exact same scene, and nearly same shade of color on the item, taken with the same or similar parameters -- it does not have the same problem.



Feb 02, 2012 at 11:03 PM
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p.1 #7 · p.1 #7 · 5dmk2, problems with pure reds (and sometimes blues)


I think the problem is that digital cameras (my 7D anyway), seem more sensitive to red light than other colours. If I take a photograph of a large red or orange object with subtle tones and shapes while the overall frame exposure may be correct the object I'm photographing has lost all it's subtle shape and tones. If I reduce the exposure to regain these the image becomes underexposed to my eye. To some extent this can be corrected in PP but I still find it a struggle to recreate the brightness and purity of colour with the tones and shapes that my eye has seen.
I put it down to the fact that a camera is different to our eyes, I now certainly pay a lot of attention to the scenes I photograph so that when I get into PP I can recreate most of what was there rather than something that looks stunning on the monitor.



Feb 02, 2012 at 11:14 PM
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p.1 #8 · p.1 #8 · 5dmk2, problems with pure reds (and sometimes blues)


This is not unique to the 5D. My 7D and shots from others using Canon seem tend to blow out the reds before other colors. Nikon seems to have a similar tendency with blues. I have noticed this and seen others comment on this as well.


Feb 03, 2012 at 12:27 AM
Pixel Perfect
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p.1 #9 · p.1 #9 · 5dmk2, problems with pure reds (and sometimes blues)


All Canon cameras have problems with reds!

Blues have been a problem since film days. Certain deep blue/violet/indigo colours are very hard to capture accurately.



Feb 03, 2012 at 12:30 AM
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p.1 #10 · p.1 #10 · 5dmk2, problems with pure reds (and sometimes blues)


You are almost certainly blowing out the red channel. First, check exposure using the histogram display. Second, be sure to set it so that you can see the three individual color channels - otherwise the average luminosity may "overlook" an overly strong level in only one of them. Third, it isn't bad idea with a subject that is very intense in one of the channels (though red is the most likely culprit) to simply under expose just a bit if possible.

By the way, as to the question of whether the histogram is "reliable" or not... it is reliable, but you must learn to interpret it.

Dan

Access wrote:
I have a problem in some of my photos, most commonly with the clothing that people wear that is mono-color, like a cap or dress that is pure red or a skirt that is a pure blue in color.

I'm not sure exactly how to describe this -- but sometimes I find that if the object is even slightly covered by shadow, the 'tonal depth(?)' is poor, or the jump from one luminance level to the next is very visible. Things end up looking like 'mush', and it shows even when viewed on a computer monitor (32-bit color) and/or resized at
...Show more



Feb 03, 2012 at 12:41 AM
 

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p.1 #11 · p.1 #11 · 5dmk2, problems with pure reds (and sometimes blues)


Access wrote:
I thought about the monitor, I checked this morning and it's the standard 32-bit color.
At least the gamma is set correctly. I can typically shift the object throughout the whole level (ie. from bright red to dark red) and it looks the same either way.

I don't think it's the monitor because sometimes a similar photo of nearly the exact same scene, and nearly same shade of color on the item, taken with the same or similar parameters -- it does not have the same problem.


bit depth has nothing to do with gamut, so it might be an sRGB monitor

as for that last bit,maybe it was exposed just a trace less, the flower was just saturated a bit less, etc. or for the darkest shades exposed just a bit more to fit whatever gamut screen you have




Feb 03, 2012 at 12:57 AM
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p.1 #12 · p.1 #12 · 5dmk2, problems with pure reds (and sometimes blues)


I do say take a look at some images with intense reds and oranages on wide gamut monitors before saying that Canon camera's blow out red. What is blown in sRGB may suddenly look realistic in a larger gamut than taming red and compressing gamut.



Feb 03, 2012 at 01:06 AM
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p.1 #13 · p.1 #13 · 5dmk2, problems with pure reds (and sometimes blues)


What's confusing to me is -- sometimes it's there and sometimes it's not. Or sometimes it's much less visible than other times. If I could figure out what's causing it, then I could probably stop it...

The RGB averaging thing is the very reason why I always use RGB histogram to check.
I shoot RAW only (no RAW+JPG) so I always assume the histogram was accurate in regards to the color levels.

And I also often use bracketing (I did a lot this last weekend -- typically [-1 0 -2] or [-2/3 0 -1 1/2]) so in many cases I have multiple exposures to choose from.



Feb 03, 2012 at 01:44 AM
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p.1 #14 · p.1 #14 · 5dmk2, problems with pure reds (and sometimes blues)


Even if you shoot RAW only, there is an embedded jpg that is used to generate the LCD preview and this jpg has a tone curve applied to it based on the picture style you have in effect.

Classic red roses for example can cause a lot of problems. The red channel can show clipping even though the green and blue are more than a stop or more from the RHS. In PP it's hard to get detail in the rose petal without desaturating. Certain reds and oranges are more problematic than others. To me it's mainly the naturally occurring deeply saturated reds that cause problem, not say a red painted object.



Feb 03, 2012 at 01:51 AM
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p.1 #15 · p.1 #15 · 5dmk2, problems with pure reds (and sometimes blues)


Access wrote:
The RGB averaging thing is the very reason why I always use RGB histogram to check.
I shoot RAW only (no RAW+JPG) so I always assume the histogram was accurate in regards to the color levels.


It would be very nice if the histograms actually reflected the RAW values; unfortunately, as I commented above, this is not really true. For a demonstration of this, take an identical exposure with two different white balance settings (e.g. tungsten and shade for a large difference). Although the sensor RAW data should be the same for the two images, the RGB histograms will be different (corresponding to the white-balance-adjusted images). Thus, even using the RGB histograms, you are seeing the results AFTER the camera has made many adjustments (including mixing the color channels for white balance, and trying to make actual clipping look less terrible).



Feb 03, 2012 at 01:58 AM
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p.1 #16 · p.1 #16 · 5dmk2, problems with pure reds (and sometimes blues)


Mine is overexposed in the red channel, but it can be brought back in photoshop. That seems to be a feature in most of the digital SLR cameras I've owned.

Taken last week. Our school play director liked red lights!















Feb 03, 2012 at 02:44 AM
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p.1 #17 · p.1 #17 · 5dmk2, problems with pure reds (and sometimes blues)


mpmendenhall wrote:
It would be very nice if the histograms actually reflected the RAW values; unfortunately, as I commented above, this is not really true. For a demonstration of this, take an identical exposure with two different white balance settings (e.g. tungsten and shade for a large difference). Although the sensor RAW data should be the same for the two images, the RGB histograms will be different (corresponding to the white-balance-adjusted images). Thus, even using the RGB histograms, you are seeing the results AFTER the camera has made many adjustments (including mixing the color channels for white balance, and trying to make
...Show more

This is what I was getting at when I mentioned that you have to learn how to read the histogram. It is not safe to presume that exposing all the way to the right is necessarily the best idea when the image is very strong in one channel. You can get a sense of how close to go, and this is one case where you can tell a bit about how things are playing out by looking at the actual LCD image on the rear display. (This is something about which I usually recommend a great deal of caution - since the LCD display is not really an accurate tool in most cases. But it can, once you learn how to interpret it, help you with identifying images that blow a color channel. )

Bracketing can also be useful.

And you'll learn to recognize certain subjects that seem especially prone to this issue: I first learned about it while shooting California poppies. Autumn colors can produce the problem, as can certain types of stage lighting.

When in doubt, under-expose a bit.

Dan



Feb 03, 2012 at 04:00 AM
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p.1 #18 · p.1 #18 · 5dmk2, problems with pure reds (and sometimes blues)


http://www.dpreview.com/galleries/2639648299/photos/1718108/example-without-htp?inalbum=examples
http://www.dpreview.com/galleries/2639648299/photos/1718109/example-with-htp?inalbum=examples
http://www.dpreview.com/galleries/2639648299/photos/1718107/bracketed-no-adjustment-3?inalbum=examples
http://www.dpreview.com/galleries/2639648299/photos/1718106/bracketed-no-adjustment-2?inalbum=examples
http://www.dpreview.com/galleries/2639648299/photos/1718105/bracketed-no-adjustment-1?inalbum=examples

Here are some screen captures of my examples, I know this site doesn't work 100% but you can at least click on original and get the image to display that way. I'd try to put them in the message itself (like the post above), uploading them on a different site that supports direct linking, but they are large files and without a preview post button, I've got no way of telling if it would work or not.

Hopefully the three bracketed pics demonstrate the problem well enough, they were taken of the same scene, though it was very windy that day so nothing was perfectly still. I've turned all my raw adjustments to 0, especially DPP's tone curve adjust since that can make things look much worse.

I used to think this was due to Highlight Tone Priority so I was turning that on only when it was needed and leaving it off otherwise. Though it turns up in photos where that is turned off too, just probably not quite as bad.

When I look at them right now, some don't look too bad but it gets much worse as I try to do any kind of post like pulling from the shadows or adjusting the tone curve. Whereas parts of the picture that aren't pure red (or in some cases, pure blue) always look just fine and are much more forgiving to whatever simple postprocessing (just contrast, highlight, shadow, tone curve, etc. adjustments) I choose to do and everything else.

ie. "off" shade of red that looks much better even with raw adjustments
http://www.dpreview.com/galleries/2639648299/photos/1718239/off_shade_of_red?inalbum=examples

And I'm not trying to 'pixel peep' I wouldn't complain if it wasn't noticeable when viewed online at typical resolutions. Even the off shade of red picture doesn't look perfect when viewed at the pixel level but it looks just fine when viewed normally. What can I try other than just learning to live with it?

And I'll keep what people are saying about the histogram in mind in the future, it does seem to make sense.



Feb 03, 2012 at 04:28 AM
skibum5
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p.1 #19 · p.1 #19 · 5dmk2, problems with pure reds (and sometimes blues)


I think it is partly that those reds are too much for sRGB monitor and, for the reds more in shadow that plus maybe a touch of 5D2 color-blindness and deep shadow noise (especially since you say those parts do better with HTP off and HTP tries to prevent channel blow out but makes shadows and dark tones worse).



Feb 03, 2012 at 04:53 AM
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p.1 #20 · p.1 #20 · 5dmk2, problems with pure reds (and sometimes blues)


Actually I was thinking about this late last night and thought of something, is this what is going on?

When the part of the photo is pure red, that means it has no green or blue component. Meaning it will only show up on the red part of the bayer array, and not the green and blue part which will be zero or close to zero. Meaning, one third (or less if the bayer doesn't favor red) the advertised resolution, and less luminence data to average over or interpolate from. The raw conversion software does the best job it can, but it can only do so much since 2/3rd or more of the data that is normally there isn't.

Because with a bayer array sensor, isn't it normally interpolating color data in order to get the full resolution and even luminence precision?

It only happens with pure red, or blue (rarer). I've never seen it with green. Red may be the worst case because the bayer favors green over blue and blue over red. I know in the old days bayers sometimes had two greens for every one blue and red, but modern day I believe the patterns are more complicated than that.

And out of habit now, I only turn on HTP if I think it's going to be necessary.



Feb 03, 2012 at 04:11 PM
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