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02-28-2014, 05:41 AM   #1
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Weird sky

Any one any idea what has happened with the sky on this shot ?

K5 with kit lens 18-55 @f11

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02-28-2014, 05:53 AM   #2
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It posterized. I'm guessing a JPEG doesn't have enough bit depth to cover all those subtle graduations of luminance, especially on a gray subject. JPEG is only 8 bits per color channel, right? So on a gray subject you only get 256 levels of luminance, and it can lead to situations like this. I'm surprised artifacts like this don't show up more often, but it really takes an unusual situation to makes them noticeable.

If you shot it in RAW, I'm just guessing it might be possible to run it through a different JPEG engine and get better results, if you have one that does dithering? Or else, it could be fixed after-the-fact with some work in GIMP or Photoshop.
02-28-2014, 06:10 AM   #3
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Shot in RAW and appears on other images ! No idea what is making this happen, previous kit lens did not do it !
02-28-2014, 06:18 AM   #4
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Very strange, very strange... Still my intuition is to blame the RAW-to-JPEG conversion. If you had some different program (meaning, different from whatever you normally use), that you could load the RAW file into, it would be very interesting to see if the effect is still visible there.

02-28-2014, 06:20 AM   #5
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What does it look like on your raw converter prior to exporting and which software are you using for your raw-to-jpeg conversion? Plus does your raw converter have the ability to export at 16 bit instead of 8 bit? I'm in the same lines of thinking as Tony that your jpeg conversion software is causing it.

Last edited by Oldbayrunner; 02-28-2014 at 06:27 AM.
02-28-2014, 06:35 AM   #6
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What software are you using? This is a JPG artifact, not optical issue.
02-28-2014, 06:43 AM   #7
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It happens with one lens but not another lens? Which lenses? What processing software? Perhaps you have different profiles setup for different lenses.

The banding definitely looks like a conversion or processing artifact. Was the original scene's light much flatter and contrast has been boosted too much?
02-28-2014, 07:04 AM   #8
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What is the jpeg quality that you used? Any filters?

02-28-2014, 07:36 AM   #9
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I have a K-30 that has a similar sensor, although not the same CMOS sensor as the K-5 and experienced that "weird" sky effect too, visible on RAW images too. I am not talking about JPGs here.
RAW files (DNG) are recorded at 4928 x 3264 pixels with 12-bit depth per pixel and they're not processed, so none of the in-camera effects are applied.
The K-30 only does 12-bit RAW as opposed to the K-5 with 14-bit RAW. This is related to "dynamic range". It seems that 14-bit depth is sometimes not enough for that kind of grey shades.
02-28-2014, 08:01 AM   #10
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QuoteOriginally posted by CristiC Quote
I have a K-30 that has a similar sensor, although not the same CMOS sensor as the K-5 and experienced that "weird" sky effect too, visible on RAW images too. I am not talking about JPGs here.
If you are seeing this effect on your RAW images, you should check your display. Probably running in a low colour mode or just bad at colours.
02-28-2014, 08:47 AM   #11
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I was so sure it would turn out his in camera JPEG quality got cranked way down by accident, as has been said that's exactly what it looks like when you save a JPEG to super low quality in an editing program. I can see the same effect in the hills there and its probably over the whole picture though most noticeable in the just the sky.

The fact that it is visible in a raw file just baffles me and it means the camera reset that would have been my first suggestion probably won't help. I would suggest the full camera reset just to see if something you are missing got changed though.

Also if it was just his display we wouldn't be seeing it.
02-28-2014, 10:17 AM   #12
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Since some software (e.g. CS6) utilizes the GPU on your graphics card, could it be possible for it to be causing this problem? I would update your video drivers, and if they're already up to date, then I'd download the current driver, uninstall the currently loaded drivers and then reinstall.

However, this doesn't address the issue of why this isn't happening on your other lens.
02-28-2014, 10:24 AM   #13
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The steps between the different gradations of light blue are too large to be accounted for by 8 bit quantisation. The encoding would need to be as low as at 6 bits per colour component to get such large steps.

Can you post the raw of that shot, maybe something can be understood from it?
02-28-2014, 10:38 AM   #14
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QuoteOriginally posted by Tony Belding Quote
Very strange, very strange... Still my intuition is to blame the RAW-to-JPEG conversion. If you had some different program (meaning, different from whatever you normally use), that you could load the RAW file into, it would be very interesting to see if the effect is still visible there.
Here is the RAW file with the same effect.

---------- Post added 02-28-14 at 10:43 AM ----------

QuoteOriginally posted by bengibollen Quote
If you are seeing this effect on your RAW images, you should check your display. Probably running in a low colour mode or just bad at colours.
Which display ought I to check ?
02-28-2014, 10:47 AM - 1 Like   #15
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I will bet all of my bitcoins that it is a JPEG artifact. In fact, I just got my kit lens and camera and took a shot that shows the JPEG artifact - but only when I create it myself in processing. My shot is with the K-7, 12 bit RAW, kit lens at the same focal length as the OP, f11, 1/180 because my camera is set for half stops, and ISO 100 because my sky is brighter. I imported the shot into Lightroom 4 but all settings are zero or neutral: WB uses the camera AWB setting, no exposure changes, lens corrections or sharpening. Then I used Photoshop CS5 to reduce the size to 1000x664. No other processing was done. If I save that file as a JPEG with quality level 12, the highest, I get this:




If I follow the same exact steps as above, but save as quality level 4, I get this:




That's not from repeated saving of a JPEG either, because I'm saving a DNG.

Remember that your shot is in RAW, but to see an image on a screen, that data has to be interpreted by software. Some software uses the preview image in the RAW file, because it's easy. Some software doesn't know enough about your camera. You can't just say "I shot in RAW and here is my terrible image" without checking all those software steps in the middle.
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