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08-17-2013, 07:18 PM   #1
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another reason to shoot RAW?

I shoot RAW+ using a K-30. I was just examining two identical images side by side; the saved jpeg and the saved RAW. I just noticed something. The RAW image has a few more pixels along all the sides. It looks like the camera is doing a slight crop when saving the jpeg image.

See what you think:
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/234303-question...ml#post2479622

Now most of the time, this slight crop will be meaningless, but there are times it could make a big difference.

08-17-2013, 07:52 PM - 1 Like   #2
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Do you have distortion correction turned on?
08-17-2013, 07:54 PM   #3
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QuoteOriginally posted by manacho2005 Quote
Do you have distortion correction turned on?
That's probably what it is. JPEGs and RAWs should contain the same recorded pixels.

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08-17-2013, 09:12 PM   #4
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I only shoot raw so never noticed but if it's so, could be because of jpeg engine is aligning size to DCT block size which is 8 or 16 pixels.

08-18-2013, 05:37 AM   #5
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QuoteOriginally posted by manacho2005 Quote
Do you have distortion correction turned on?
Bingo! You win the blue ribbon - I think. I guess I don't know enough about what in-camera distortion correction does mechanically with image data to blindly say 'that's it'. I'll take a couple test shots within the next day or two with distortion correction off and see what happens.

If that IS the issue, I can certainly live without it as any image that matters comes from the RAW version of the file anyhow. And obviously this control does nothing to those files.

Stay tuned....
08-18-2013, 05:42 AM   #6
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QuoteOriginally posted by yusuf Quote
I only shoot raw so never noticed but if it's so, could be because of jpeg engine is aligning size to DCT block size which is 8 or 16 pixels.
Tests will tell. If anybody else wants to run a couple tests shooting RAW+, please do!
08-18-2013, 08:19 AM   #7
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I leave it off as well as "chromatic correction" because it slows down the camera. If you only shoot RAW I suggest you leave both off as well as "highlight and shadow correction" , it only affects jpeg and the preview.
08-19-2013, 12:10 PM   #8
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QuoteOriginally posted by manacho2005 Quote
I leave it off as well as "chromatic correction" because it slows down the camera. If you only shoot RAW I suggest you leave both off as well as "highlight and shadow correction" , it only affects jpeg and the preview.
It seems unlikely that highlight or shadow correction slows down the camera. Shadow correction is not applied in RAW (so it makes sense to have it off). Highlight correction will change effective ISO, and provides instruction to the converter, but has no significant impact on processing. Purists can opt not to use HC as a matter of principle, but when conditions warrant it - great to have, allowing you to turn your attention to other details related to composition, etc.

08-22-2013, 09:07 AM - 1 Like   #9
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I had my first chance since starting this thread to compare the RAW+ jpeg and DNG images with distortion correction turned off. I can confirm that this is the reason for my missing pixels. Apparently - at least with a lens that has little distortion - the camera 'solves' any possible distortion by simply whacking off a few pixels from each edge of the frame where it would be most obvious. I suppose this is a way to minimize the appearance of both pincushion and barrel distortion as well as minor vignetting.

Frankly, I can do just as well by applying a minor crop in PP - when necessary. I see little reason to turn this feature back on.

Thanks again to manacho2005 for the first correct response!
08-22-2013, 04:14 PM   #10
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QuoteOriginally posted by JimJohnson Quote
I had my first chance since starting this thread to compare the RAW+ jpeg and DNG images with distortion correction turned off. I can confirm that this is the reason for my missing pixels. Apparently - at least with a lens that has little distortion - the camera 'solves' any possible distortion by simply whacking off a few pixels from each edge of the frame where it would be most obvious. I suppose this is a way to minimize the appearance of both pincushion and barrel distortion as well as minor vignetting.

Frankly, I can do just as well by applying a minor crop in PP - when necessary. I see little reason to turn this feature back on.

Thanks again to manacho2005 for the first correct response!
It is a little more sophisticated in profiling the lens than just eliminating the edges. By correcting for distortion, you have to eliminate edges. I don't know anyone who routinely shoots architecture in JPEG, but if you do that would be a good reason to turn on the correction.

As a matter of strong preference, I generally preserve some barrel distortion when shooting wide angle. When shooting groups, rectilinear distortion (rectilinear projection is a severe form of distortion) is pretty offensive compared to stereographic or other mild forms of barrel distortion.
08-23-2013, 12:37 AM   #11
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QuoteOriginally posted by ScooterMaxi Jim Quote
It is a little more sophisticated in profiling the lens than just eliminating the edges. By correcting for distortion, you have to eliminate edges. I don't know anyone who routinely shoots architecture in JPEG, but if you do that would be a good reason to turn on the correction.

As a matter of strong preference, I generally preserve some barrel distortion when shooting wide angle. When shooting groups, rectilinear distortion (rectilinear projection is a severe form of distortion) is pretty offensive compared to stereographic or other mild forms of barrel distortion.
When you correct for barrel or pincussion distortion you end up with the borders of the photo being curved, concave for barrel correction and convex for pincussion. The image therefore has to be cropped just enough to maintain a rectangular border.
08-28-2013, 12:13 PM   #12
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QuoteOriginally posted by ScooterMaxi Jim Quote
It seems unlikely that highlight or shadow correction slows down the camera. Shadow correction is not applied in RAW (so it makes sense to have it off). Highlight correction will change effective ISO, and provides instruction to the converter, but has no significant impact on processing. Purists can opt not to use HC as a matter of principle, but when conditions warrant it - great to have, allowing you to turn your attention to other details related to composition, etc.
Both of these still have some impact on camera operation even when shooting RAW only - at least they do on the K7 and I've not heard anyone say the K5 is different in these respects.

I've heard it said before that having them active reduces burst speeds - thats not my experience. What I have seen happen is that the Digital Review image on the LCD screen is slower to appear, either after a single shot or the final image of a burst.

This is because the processing is applied to the JPEG preview I believe, and these functions take extra time. When opening the RAW file in PDCU then the settings will be activated by default, but I do not believe they will have any affect in other RAW conversion software.
08-28-2013, 12:22 PM   #13
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QuoteOriginally posted by ScooterMaxi Jim Quote
Snip........

As a matter of strong preference, I generally preserve some barrel distortion when shooting wide angle. When shooting groups, rectilinear distortion (rectilinear projection is a severe form of distortion) is pretty offensive compared to stereographic or other mild forms of barrel distortion.
I quite agree, there was an interesting post recently that compared several ultra wides with a landscape shot, and one lens was the 10-17 fisheye. It produced closer to what the eye actually sees, than a rectilinear corrected UWA
08-28-2013, 12:27 PM   #14
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QuoteOriginally posted by JimJohnson Quote
I had my first chance since starting this thread to compare the RAW+ jpeg and DNG images with distortion correction turned off. I can confirm that this is the reason for my missing pixels. Apparently - at least with a lens that has little distortion - the camera 'solves' any possible distortion by simply whacking off a few pixels from each edge of the frame where it would be most obvious. I suppose this is a way to minimize the appearance of both pincushion and barrel distortion as well as minor vignetting.

Frankly, I can do just as well by applying a minor crop in PP - when necessary. I see little reason to turn this feature back on.

Thanks again to manacho2005 for the first correct response!
But you need to consider a minor crop will still leave obvious distortinn in the middle of the frame, the distortion correction works across the whole frame but when cropping to return the image to rectangular, the largest amount of cropped data is at the edges, so you see this first.

My editor, Corel's PSP X5 gives you the option of cropping or not when doing corrections. You should see the result from severe distortion and the amount of what gets cropped
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