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09-26-2010, 06:33 PM   #1
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RAW Compression artifacts?

Since I am not sure what is causing this phenomenon, although it reminds me of a jpeg image that has been compressed. I just purchased a basic Hoya HMC UV filter and used it for the first time - never had this crop up before. Any images I took with the sky in it showed this to varying degrees, but only in RAW ( DNG), jpegs at the highest quality settings are fine. Anyone have an answer for this? I have yet to take some pictures with the filter removed in case this is the problem, seems kind of odd though. I am using FastStone to download the images if that matters. I'm fairly new to digital photography so maybe I am missing something. The camera is a K20D with the DA 16-45 lens.






Last edited by Johnny5; 09-26-2010 at 06:40 PM.
09-26-2010, 07:15 PM   #2
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Are you referring to the streaking across the sky where it changes shades or are you talking about the dirty sensor? I would dump the filter. Your processing software may also be over compressing the RAW files when you create the JPGs. RAW files (DNG PEF) are not photos but only data to create photos. The software you use Can make a difference in output. If you want to go the freebie route, try The Gimp.

09-26-2010, 08:18 PM   #3
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This thread was started earlier with the same problem and same software. Maybe there was an update that broke the raw software for faststone.

https://www.pentaxforums.com/forums/pentax-dslr-discussion/115941-k-7-banding...rsion-jpg.html
09-26-2010, 09:30 PM   #4
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I've seen this before. It was described to me as

"
The weird things you are seeing are just quantization artifacts. I'd guess that the photo is slightly underexposed: These artifacts get more pronounced at lower levels, where each bit has to represent a larger portion of each f-stop. By "underexposed" I mean that the original shot was probably exposed properly as far as the "look" of the scene goes and didn't have any clipping, it just didn't have the histogram pushed all the way to the right. With bright photos like this, pushing the histogram to the right yields an overly-bright, washed-out-looking image, but one that can be brought into line in Raw conversion. Without those artifacts (usually). You've really got a "worst case" situation with this shot because you have a really gradual transition of a fairly narrow range of tones over a very wide area."

By someone who knows what they are talking about.

09-26-2010, 10:13 PM   #5
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Thank you enoeske and everyone else for helping me understand what was happening, I just had never come across it using FastStone with many other images previously. Maybe it is time for Lightroom or something similar!
09-27-2010, 01:49 AM   #6
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QuoteOriginally posted by Johnny5 Quote
Thank you enoeske and everyone else for helping me understand what was happening, I just had never come across it using FastStone with many other images previously. Maybe it is time for Lightroom or something similar!
When it happened to me, it was Lightroom that had done the conversion.
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