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08-16-2010, 11:01 AM   #1
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Saturation of Pentax dSLR Images

Shooting the other night - I noticed that I was getting images from my K-x that looked very saturated.

Now Pentax dSLRs used to have a reputation of giving very saturated images on their default "Bright Color" setting
eg: from dpReview on K100D:
" The K100D's color response was quite similar to that of previous Pentax digital SLR's, that is quite highly saturated (vivid) in the default 'Bright' image tone, as can also be seen earlier in this review, it can lead to color clipping in certain situations (such as red flowers in direct sunlight). Switching to the Natural tone calms color saturation to more typical levels (compared to other digital SLRs). "
On the K100D I have Natural Color set.

However with more recent Pentax dSLRs like the current range of K-x and K-7 -
from dpReview on K-x -
" The K-x produces an almost identical color response to its bigger brother, the K-7. As we've seen in other reviews the standard hues are also very similar to most other SLRs in this class, with minor saturation and brightness differences but essentially the same color response. "

So with the current Pentax dSLRs like the K-x and K-7 the saturation is in line with most other competitors.

Having experience with the K100D - the first thing I did was to change the default Bright color setting on the K-x to Natural -
but the reduction in saturation was enough that I soon switched back to "Bright" as it gave me pictures more the way I wanted them.

OK back to the other night - here's an example of what I mean:

EXIF still attached (caveat - PhotoBucket often mysteriously drops metadata) -
only adjustments was to resize, brightness/contrast and standard sharpening -
this looks way over-saturated to my eyes -
so much so, for my posted version I had to reduce saturation by -24/100 in my photo editor PhotoImpact 8 (-100/100 would produce a black and white photo - ie: all color is removed) -


That photo was overall over saturated - however other than magenta (please see: Modern LED Stage Lighting & photography problems ) - I think a lot of problem stems from saturation of Red -


compared to a shot taken only seconds apart on my Canon G10 compact -

notice the face of the bass player on the right of the picture, and drummer in front of the red lit screen in almost merged with the screen.
The Canon G10 seems to show reasonable details in the faces - yet the K-x picture appears to have over-saturated on the red leaving very little detail in the faces.

I tired to reduce the saturation again by -24/100 -

it is better, but the faces details are not really revealed.......

A shot from further back show a different treatment of overall red -
K-x "as is"-


Canon G10 -


K-x reduce saturation by -24/100


some really strong lighting -
K-x "as is"


G10 -


K-x reduce saturation -24/100 -

again the red in the face of the drummer on the right is never revealed -
due to the over saturation in red.......

I also tried using "Natural Color" setting for reduced saturation - but it did not seem to help that much - at least when reviewed on the K-x LCD monitor.

08-16-2010, 11:22 AM   #2
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The image quality is pretty poor so it's hard to judge what's going there.

With that said, it seems to be a challenging lighting condition. It's a high contrast scene with an extremely warm color temperature. The musicians are brightly lit and the background is pretty much unlit.

My guess is that you over exposed most of these images, causing the red channel to clip. Deep saturated blues and reds tend to get clipped on the K-x and probably most DSLRs. To offset it, I use lenses with great color reproduction in the red and blue channels like the A35-105mm f3.5 and I under expose the image by half a stop in RAW. That solves most of the color issues. You seem to have metered the wall and surrounding instead of the musicians.
08-16-2010, 11:31 AM   #3
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QuoteOriginally posted by hangu Quote
You seem to have metered the wall and surrounding instead of the musicians.
Thanks for your input -
really? the musicians are incorrectly exposed?
and the image quality is really that poor that one cannot see the over-saturation in Red?
However that was the point the details in the red areas are masked or degraded.

Yes, of course it's the strong lighting - but the treatment by the Canon G10 is different enough to show a difference in the red areas.

Normally I do not have that problem as shown by the numerous photos posted in my long thread: Kx in Use - this is the first time I have noticed how grossly over-saturated the K-x images were and how difficult the red areas turned out.

Thanks for the comments.
08-16-2010, 11:39 AM   #4
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I know this may not be helpful, but if there's one thing I've learned with low light shooting it's that each camera has it's own set of rules. Though one of the most significant steps is taking an external WB reading whenever possible. The second alternative is to use a WB cap and of course the last being AUTO.

Another really helpful step in getting the shot is to review and adjust images as I go along. And though not always convenient of possible(in the heat of the moment), it often becomes the only way for which to keep things in check with respect to managing things under difficult lighting.

Though something tells me that you might have gotten away with better shots by adjusting your exposure zones and perhaps(worst cases scenario) adjusting the red channel in your scenes. However... I think WB should have taken care of the color casts for the most part.

08-16-2010, 11:49 AM   #5
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QuoteOriginally posted by UnknownVT Quote
really? the musicians are incorrectly exposed?
These things are subjective, but for my tastes, the dude in blue is pretty overexposed in most of the shots. Seems to have lost detail in the face and hair. Less exposure might have also addressed some of the saturation issues, which are perhaps caused in part by channel clipping. Still, a really surprising difference on the bassist's face between the K-x and G10.
08-16-2010, 12:10 PM   #6
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I can see the red channel clipping but the JPEG artifacts caused by image compression certainly aren't helping. A free Flickr account should solve that. A higher quality image would certainly help us in diagnosing the problem.

The white pattern on the left musician is clearly over exposed in the yellow channel. The musician's hair and face in the center is also clipped. It seems the stage lights are of different color. There are magenta lights on the right and yellow lights on the left. That's why the yellow channel is clipped on the guy on the left and the red channel is clipped on the guy on the right. They're also not evenly lit.

Edit: My suspicion is confirmed in this photo:
http://img.photobucket.com/albums/v71/UnknownVT/Kx/bkStageKxAsIs100813.jpg
Check the lights on the top left. Different color lights.

I've had similar issues in bar concerts. Lens coating seems to play a big part in the image quality. My Voigtlander and A series lenses fared better than my Super Takumars when it came to over saturation.

Last edited by hangu; 08-16-2010 at 12:17 PM.
08-16-2010, 12:13 PM   #7
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QuoteOriginally posted by UnknownVT Quote
Thanks for your input -
really? the musicians are incorrectly exposed?
and the image quality is really that poor that one cannot see the over-saturation in Red?
However that was the point the details in the red areas are masked or degraded.

Yes, of course it's the strong lighting - but the treatment by the Canon G10 is different enough to show a difference in the red areas.

Normally I do not have that problem as shown by the numerous photos posted in my long thread: Kx in Use - this is the first time I have noticed how grossly over-saturated the K-x images were and how difficult the red areas turned out.

Thanks for the comments.
Hi. It's an intersesting problem.

Your exposures look good to me. Oversaturated red is quite evident in the loss of detail in red areas. Can't say whether the red is actually clipped or just on the verge of being clipped. The oversaturation is really extreme, possibly to due the spectral characteristics of the light sources.

How to deal with it?

For the current images, try reducing the saturation or brightness of red specifically. My impression is that you've been doing an overall saturation reduction.

If you're shooting RAW, your chances of recovering detail in the oversaturated areas are reasonable.

I don't know PhotoImpact 8 so can't be specific about how you would do this. If PhotoImpact has some sort of Curves function that allows you to select individual colours, that might be a starting point, as would some sort of hue/saturation function.

Prevention?

1. If you're not shooting RAW, do so. It won't necessarily produce correct color, but it will give you a lot more information than JPEG for corrective purposes.

2. I presume you can set up a custom profile in your KX with reduced red saturation. I would do this by testing on a red target (preferably something illuminated with tungsten light and a red gel). This would emulate concert lighting somewhat. Review results on your computer monitor using your photo editor to view curves and if possible a histogram of the individual colours. This is more reliable than using your camera's monitor.

Hope this helps.

John
08-16-2010, 12:20 PM   #8
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QuoteOriginally posted by John Poirier Quote
Your exposures look good to me. Oversaturated red is quite evident in the loss of detail in red areas.
John
I'm fairly certain over saturation in a channel is caused by over exposure of said channel....

08-16-2010, 12:27 PM   #9
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QuoteOriginally posted by Marc Sabatella Quote
but for my tastes, the dude in blue is pretty overexposed in most of the shots. Seems to have lost detail in the face and hair. Less exposure might have also addressed some of the saturation issues, which are perhaps caused in part by channel clipping. Still, a really surprising difference on the bassist's face between the K-x and G10.
QuoteOriginally posted by hangu Quote
The white pattern on the left musician is clearly over exposed in the yellow channel. The musician's hair and face in the center is also clipped. It seems the stage lights are of different color. There are magenta lights on the right and yellow lights on the left. That's why the yellow channel is clipped on the guy on the left and the red channel is clipped on the guy on the right. They're also not evenly lit.
Sorry the "exposure" was entirely my fault
I did brightness/contrast adjustments in PhotoImpact 8 to bring out the picture and details - to my tastes.

The lighting was uneven, and mixed colors - as that was the stage lighting I was shooting under - no convenient way of doing any manual white balance as the lights also changed.....

Here are the originals resized and standard sharpened only:








there is degradation loss of details due to the red compression in JPG used.
08-16-2010, 03:56 PM   #10
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QuoteOriginally posted by UnknownVT Quote
Sorry the "exposure" was entirely my fault
I did brightness/contrast adjustments in PhotoImpact 8 to bring out the picture and details - to my tastes.

The lighting was uneven, and mixed colors - as that was the stage lighting I was shooting under - no convenient way of doing any manual white balance as the lights also changed.....

Here are the originals resized and standard sharpened only:








there is degradation loss of details due to the red compression in JPG used.
Hi Vincent. To my taste the originals are better than the edited versions. Just fine given the conditions, I'd say. Nice work!

JPEG artifacts or not, the reds are oversaturated, so I'd still try the remedies I suggested earlier. (Very saturated reds are not unusual in DSLRs in my experience. I've seen similar things with both Nikon and Kodak gear. Nothing to panic about.)

John
08-16-2010, 05:00 PM   #11
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QuoteOriginally posted by hangu Quote
I'm fairly certain over saturation in a channel is caused by over exposure of said channel....
QuoteOriginally posted by John Poirier Quote
JPEG artifacts or not, the reds are oversaturated
(Very saturated reds are not unusual in DSLRs in my experience. I've seen similar things with both Nikon and Kodak gear. Nothing to panic about.)
Many thanks for the input and suggestions - like I said I haven't had too much problems with gross over saturation - until those shots from the other night and I shoot a lot with the K-x (shot count 16,567).

However if there is a tendency to over saturate -
then the exposure becomes more critical -
as it becomes easier to over expose -
because the color(s) over-saturate -
kind of chicken and egg situation - they are inter-related -

Here's an example again only resize and sharpen -
but knowing there is problem of JPG compression degradation/loss in red - I did everything I knew how to minimize this - PS Elements resize bicubic sharper, enhance sharpen with remove of lens blur - then save as JPG using preview to find a level/quality that show little to no difference between the preview save and the image in the editor (used PSE level 8)

yes, obviously right directly in the red light -
notice how the over saturation mushes up the face detail -
I don't think it is straight over exposure
since if I remove the colors by desaturation leaving only the luminance -
it looks like:

the face remains mushy and flattened
but surely it wasn't really over exposed -
otherwise it would be closer to white?

As always comments, critiques and suggestions are welcome.
08-16-2010, 08:53 PM   #12
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QuoteOriginally posted by UnknownVT Quote
Many thanks for the input and suggestions - like I said I haven't had too much problems with gross over saturation - until those shots from the other night and I shoot a lot with the K-x (shot count 16,567).

However if there is a tendency to over saturate -
then the exposure becomes more critical -
as it becomes easier to over expose -
because the color(s) over-saturate -
kind of chicken and egg situation - they are inter-related -

Here's an example again only resize and sharpen -
but knowing there is problem of JPG compression degradation/loss in red - I did everything I knew how to minimize this - PS Elements resize bicubic sharper, enhance sharpen with remove of lens blur - then save as JPG using preview to find a level/quality that show little to no difference between the preview save and the image in the editor (used PSE level 8)

yes, obviously right directly in the red light -
notice how the over saturation mushes up the face detail -
I don't think it is straight over exposure
since if I remove the colors by desaturation leaving only the luminance -
it looks like:

the face remains mushy and flattened
but surely it wasn't really over exposed -
otherwise it would be closer to white?

As always comments, critiques and suggestions are welcome.
I suggest that the face can be overexposed without being white. What a Bayer pattern sensor has is two green, one blue and one red pixel. (2 green to mimic our eyes yellow-green sensitivity). If only red is in the lighting, it will blow out as it has here, but will not blow out to white because the other three sites have no input.

I'm not sure about the K-X, but my K10 allows me to review with all colours in the histogram individually. In difficult lighting such as you have here, I would chimp the colours as well as the whole image. It might be quite revealing and lead you to underexpose to compensate. Unfortunately, the next act you see may have a completely different lighting setup, and you start all over again. Isn't photography fun?
08-16-2010, 09:51 PM   #13
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Thanks for the input so far - lots to consider.

I took the advice that John Poirier gave about reducing the saturation only in red - as opposed to overall saturation. PhotoImpact 8 allows saturation over a range of colors - on the difficult shot from the back of the stage I varied the range with the saturation setting at -100 (ie: totally desaturated) to see when the red is removed from the affected area - then I re adjusted the saturation level to get the best result by my eye -

this has improved the image somewhat - but obviously I could not recover detail that was originally lost due to the gross over-saturation and combined with the possible/debatable over-exposure in the red area.

As that was somewhat successful I tried the same on the other examples:

this shot has improved the most from reduction in red saturation - but it cannot recover the loss in detail due to the over-saturation in red in the first place. Just go back to post #1 and look at the Canon G10 shot for comparison.


again this is the best version.

the below was a strange result -

there is very strong red left on the face - that as suggested may well be over exposed - hard to tell from the original non saturation reduced shot - and notice that is almost 50% reduction in saturation - so I think I can conclusively say the main culprit is the over-saturation in red than a simple over-exposure - there is over-exposure - but it is probably due to the gross over-saturation in red - rather than the other way round.
Probably the correct term for this is clipping the red channel?

Lastly the shot that got me started on all this over saturation thread:

reducing saturation in red was not enough - I thought the blues were over saturated - so I selected blue and reduced that saturation - then there was still over saturation in yellow - so I reduced that as well - so this ended up as a 3 pass reduction in saturation red, blue and yellow.

Note: - I consider all these images dark and would adjust brightness/contrast to bring the levels up - for my tastes -
but I present them like this so there are no doubts about over-exposure.
08-17-2010, 08:07 AM   #14
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FWIW, the last one now strikes me as well-exposed overall, but as is usually the case in concert photos, could use an exposure *curve* adjustment to adjust the midtones and/or shadows relative to the lights. I'd probably be trying to bring out the midtones, leaving the deep shadows where they are or even darkening them. With ACDSee, the Lighting tool is the magic wand that pretty much no other application can really replicate, but in other applications, the "Fill Light" and "Curves" controls can be used to re-distribute the values in the image.

Last edited by Marc Sabatella; 08-17-2010 at 10:14 AM.
08-17-2010, 09:34 AM   #15
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QuoteOriginally posted by Marc Sabatella Quote
FWIW, the last one now strieks me as well-exposed overall, but as is usually the case in concert photos, could use an exposure *curve* adjustment to adjust the midtones and/or shadows relative to the lights. I'd probably be trying to bring out the midtones, leaving the deep shadows where they are or even darkening them. With ACDSee, the Lighting tool is the magic wand that pretty much no other application can really replicate, but in other applications, the "Fill Light" and "Curves" controls can be used to re-distribute the values in the image.
Yes indeed I use the fill-light tool now often - especially when the shot becomes too contrasty when using plain brightness/contrast.

Here's that last shot adjusted the best I can with the advice given to use saturation reduction in only the colors that looked over saturated - in this case red, blue and yellow - I used a -100/100 setting to isolated the colors - ensuring I was only affecting the range of those colors. Then adjusted the slider to get the best balance in that area by eye.

Since I consider any image I get straight out of the K-x to be on the (slightly) dark side - I did more post processing - in this case some fill-light then a final brightness/contrast adjustment - sharpen and that was it - this is the "best" of the versions since I started experimenting and I did it without reference to any other earlier attempts/samples - caveat - remember this is to my tastes - I like contrasty shots and do not mind if certain areas may seem over exposed (to others) in the post processed image - as that is part of the overall feel of the image (for me).

However as I know real in camera overexposure can lose details - I shoot like slides - not only do I have highlight correction (protection) On - my default exposure setting is -1/3 stop EV, and I often use exposure compensation when I chimp and see a shot not looking right.



compared to -


I can laugh now -
because my original attempt and posted shot is the lower version
and overall I think prefer that one (which only used overall saturation reduction)
as I think I may have over done the reduction in red saturation in my latest attempt -
so that the red guitar does not look as vibrant in the upper version.

Remember I processed the latest version without any reference to any previous versions -
just tried to get the pic to the best I can -
and I ended up with a result - at least to my eyes that's similar to the original "novice" overall saturation reduction attempt .
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