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10-04-2007, 08:17 AM   #1
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colour shift on long exposures

I got my K10D about 4 days ago and I am generally pleased with the photos. I can tell by reading many of the posts that there are still many issues around picture quality, sharpness, resoloution, etc. to deal with. I am not new to photography but I am new to digital photography.

I have just discovered that long exposures (about 1/2-2 secs.) come out with a very blue, almost violet cast. I am attaching two photos to show the blue casting.

My question is, what is the best way to deal with this issue? I admit I was shooting in overcast light and that may account for some of the blue cast, but it looks rather severe to me. Theexposures were also way out from the cameras selection and I had to bracket toward underexposure.

JMR


Last edited by JMR; 10-08-2007 at 11:53 AM.
10-04-2007, 09:07 AM   #2
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Can you give us some information as to your camera settings?

Honestly, they don't look overly blue to me, but they could stand a little warming up if that's your preference. If your using Auto White Balance (AWB) that would explain it. In my experience, and in reviews I've read, the AWB doesn't work as expected. The AWB setting in my Panasonic TZ3 works far better.

I've not had any problems regarding IQ and sharpness from my K10D, but that's because I always shoot RAW. The in camera jpeg processing is known to be a little more flat and soft than one would expect from a 10+ megapixel DSLR.

Hope this helps.
10-04-2007, 09:07 AM   #3
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Many things could be done. Use the channel mixer to drop the blue channel by 15-20%; or the curves dialog and set a neutral point.

QuoteOriginally posted by JMR Quote
I got my K10D about 4 days ago and I am generally pleased with the photos. I can tell by reading many of the posts that there are still many issues around picture quality, sharpness, resoloution, etc. to deal with. I am not new to photography but I am new to digital photography.

I have just discovered that long exposures (about 1/2-2 secs.) come out with a very blue, almost violet cast. I am attaching two photos to show the blue casting.

My question is, what is the best way to deal with this issue? I admit I was shooting in overcast light and that may account for some of the blue cast, but it looks rather severe to me. Theexposures were also way out from the cameras selection and I had to bracket toward underexposure.

JMR
10-04-2007, 11:55 AM   #4
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Have you updated your firmware to resolve a long exposure banding issue?

10-04-2007, 12:33 PM   #5
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Color shift

Like you, I've only had my K10D for a short time (two weeks). Like you, I'm still learning the camera. Like you, I'm not new to photography, but new to digital photography in general and the K10D in particular.

Like grounloop, I don't see that you pictures are particularly off-color, but, then I wasn't there when you shot them. You can remember what the colors really looked like. I can't.

However, in my short time with the camera, I've found that AWB doesn't handle non-daylight conditions too well. I've found that simply setting it for "Cloudy" makes a noticeable improvement in the colors. Try that.

For the last couple of days, I've been making a deliberate effort to train myself to think about the white balance before almost every shot. I've taken a lot of shots under different lighting conditions, while using different WB settings to see the difference.

This is something that, with film, we had less control of, without resorting to expensive filters that cost two or three stops. Consequently, most photographers didn't bother. With the K10D, it is much more convenient to set the WB correctly. You can modify certain color channels or set the WB to a specific color temperature. You can also boost the contrast and/or color saturation.

I have my K10D set to "forget" the white balance setting when I power it off. Before I did that, I found that I would take a shot or two with a non-standard WB setting, forget that I did, and find the next day that it was still set to tungsten or fluorescent lights.

I've also found that I much prefer the exposure when I set the EV compensation to +1.0 and leave it there. I seldom shoot at EV +0.0.

Paul Noble

Last edited by noblepa; 10-04-2007 at 12:34 PM. Reason: mispelling
10-04-2007, 06:04 PM   #6
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I can't recall how to find the specs and don't recall any of the settings. I do know I have never taken the settings off AWB, and have only altered the ISO to 100 and switched to aperture priority and almost always use manual focus.

I am attaching a redone image and have altered the brightness and raised the orange colour channel to counteract the blue-magenta bark. On my monitor, the colour cast is extremely blue-magenta where ever there is grey or white, in the the bark area on the old photo.

Thanky you all. I am learning a lot. I will try the cloudy setting in the shade and on cloudy days. I just hate to come home with a lot of orange-cast photos if the camera can handle most of the situations. This the first image I have altered since obtaining the new camera.

JMR
10-04-2007, 06:13 PM   #7
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Sorry, I screwed up the upload. Here is the photo again.

Last edited by JMR; 10-08-2007 at 11:53 AM.
10-04-2007, 08:40 PM   #8
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Color shift

QuoteOriginally posted by JMR Quote
I can't recall how to find the specs and don't recall any of the settings. I do know I have never taken the settings off AWB, and have only altered the ISO to 100 and switched to aperture priority and almost always use manual focus.JMR
If the image is sitll in the camera, it couldn't be easier. Just display the image, then press the INFO button. It has several levels. The first level shows basic stuff like shutter and aperture. Then it shows a histogram of the light levels. Press it a third time, and the picture drops to a thumbnail and most of the LCD is filled with all kinds of information, including the basics, plus ISO, WB setting, focal length, where on the image the focus spot was, EV compensation value, and a lot more.

If the image has been uploaded to your computer, the info is stored in the EXIF data as part of each file. The Pentax software that came with the camera can display this information, as can many other image editting software packages.

Paul Noble

10-05-2007, 05:41 AM   #9
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I thought color shift was not at issue in DSLRs.

In film it is called reciproscity failure. , specifically the film's sensitivity to light is not consistant at long exposures, with color film, the problem is all 3 colors have different inconsistancies, causing the color shift.

If you are concerned about color shift during exposure, set your camera to manual white balance (to eliminate any automatic influence the camera may make) and take a series of photos of the same subject, under constant lighting, at different exposures. I.e. wide open and high shutter speed, and stopped down to minimum apature and several seconds.

Using a photo editing program, you can view the histograms, color by color, and look at the average values. If they change, you have had a color shift.

Note that (at least in PSP any version) that the histogram has an approximate value of 50 per stop in the middle range from 25-225 it becomes non linear outside this range. I am not sure about Adobe products, but they are probably similar.

With this test we can discuss facts not perceptions
10-05-2007, 08:09 AM   #10
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On my monitor, the colour cast is extremely blue-magenta where ever there is grey or white, in the the bark area on the old photo.

This is another caveate. Are you using an LCD or a CRT? CRTs should be set for 5400-6200K for natural daylight color. They usually are set at the factory much higher, which gives everything a bluish cast. An LCD may not allow you to adjust the color temp at all.

I have seen some really awful monitors for color rendition out there. I wouldn't trust the colors unless you have had the monitor calibrated. Do the images look bad on other people's computers? Do the images look "off" after you get them printed at a photo finishing place?

Have you updated your firmware?
10-05-2007, 10:17 AM   #11
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Let's go back and summarize

- is there color shift as a function of exposure time (the origonal question , and a test offered to check this but no data)

- is there an issue with poor (non ideal) selection of white balance in the photos (from the posts, I think the answer is yes)

- is there an issue of color temperature of individual moniotors (from the posts, also yes)

We need to answer the origonal question.
10-05-2007, 12:27 PM   #12
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Thanks to all again for the info.

I checked firmare and have version 1. Is this the latest?

I will run the checks suggested by Lowell and let everyone know know what I come up with. I am going on an outing this Thanksgiving weekend and will run the checks. I have to say though, as far as daylight without cloud or shade, the colours appear spot on.

I don't think my monitor can be altered for temperature. I have a 22 inch Vision Quest, which appears to be very good, at least to the eye. As well, if my monitor has a magenta-blue cast, would this not show up for all photos, especially on white subject matter? Yet it appears not to. See attached photos- white fence is good. Second one, shady areas and trees not blue. Only difference is that exposures not long and sky is not overcast. Only tests will tell.

I will try to alter the white balance with and without cloudy mode, when in overcast or shady conditions and see what I come up with. Will also try setting colour balance on manual as suggested, so thanks.

JMR

Last edited by JMR; 10-08-2007 at 11:53 AM.
10-05-2007, 09:10 PM   #13
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Firmware.

Pentax Imaging - Software & Firmaware Updates

These links below show a bit of the banding problems in the old firmware.

Pentax 10D – A Hands-On Report
Horrible K10D banding iso 400+: Pentax SLR Talk Forum: Digital Photography Review
(Click on the picture in the above link to get a full view)

I just wonder if this is the problem – it seems to be a peculiarity of long exposures on the old firmware.

I read a bunch of reviews before I bought mine, and the first thing I did was update the firmware – so I have no first hand experience with your problem, but it sure is reminiscent of the stuff I’ve read.
10-05-2007, 11:36 PM   #14
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QuoteOriginally posted by JMR Quote
(snip) (snip) I have just discovered that long exposures (about 1/2-2 secs.) come out with a very blue, almost violet cast. (snip)

What I'm seeing, especially noticeable in the second image, is a variation of purple fringing - purple tint that has bleed into the surrounding picture areas. This is dealt with the same way as most other purple fringing. Either obtain a purple fringe filter for your image editing software or learn how to edit the purple tint manually. Search the internet for "purple fringing" and your software. Luckily, purple fringing is a relatively minor issue with DSLR's, only occuring in certain conditions (contrasty images with long exposures, etc).

stewart
10-06-2007, 12:29 AM   #15
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QuoteOriginally posted by JMR Quote
(snip) I am attaching a redone image and have altered the brightness and raised the orange colour channel to counteract the blue-magenta bark. On my monitor, the colour cast is extremely blue-magenta where ever there is grey or white, in the the bark area on the old photo.

Wow, JMR. Whatever you did here (the third image) is far better than most purple fringe and similar filters. How did you do that by just adjusting the brightness and raising the orange channel? The next time I take an image like this, I'll have to try the same tactics.

stewart
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