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07-12-2016, 08:50 PM   #1
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Alternative Crop Mode for APS-C lenses on K-1: Square Images

A quick review of the K-1 manual indicates that when it is used in crop mode for APS-C lenses (such as the DAs), the pixel dimensions of the cropped frame are 4800x3200, out of the full pixel dimensions of 7360x4912.

A bit of quick arithmetic (multiply the full pixel width by 1/1.5 = 2/3, the nominal crop factor) indicates the crop width should be more like 4900 pixels. Why did Pentax choose 4800? I suppose it is a nice round number, whereas 4906x3275 (the actual 2/3 values) aren't quite so "nice."

More interestingly, however, it seems to me that another crop mode would be very nice to have: a "square" picture mode, on the order of 4900x4900 pixels. The width of this square would be about what Pentax is offering, and the height would fit just right into the full frame height of 4912 pixels.

Perhaps Pentax figures we are all so used to the standard (from 35mm film days!) 1.5:1 width to height ratio for images, that we don't want anything else. However, assuming that a normal APS-C lens produces uniform quality imaging in all directions (i.e. same height as width (actually round), even though we usually throw away the extra height resolution), the extra height pixels should have just as good image quality as the outer width pixels.

And, many folks are actually used to square(er) images (old 120 film), as well as the top-end Pentax 645 series, which produce a squarer image than 1.5:1 (I think).

Of course, you can always crop it yourself in PhotoShop or whatever your favorite post-processing program is, but it would be nice for Pentax to offer this as a built-in option.

And yet another mode could be a "vertical" crop - the standard rectangular shape, but with the long direction vertical. You could take portrait orientation pictures without turning the camera sideways!

Am I missing something? Thoughts?

07-12-2016, 09:06 PM   #2
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This could be a good idea for the next model, which should then also have the corresponding crop frames available in the viewfinder.

There's a little bit of leeway in terms of effective pixels and sensor sizes. Sensors usually have more pixels on them than they actually use, to ensure clean edges. I guess 4800 just worked out for some reason or another!

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07-12-2016, 09:18 PM   #3
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Given the LCD technology seems to work well in the current version, I would hope they'd move to a more flexible arrangement in the next one, which would allow a variety of crop modes, that surely wouldn't be too difficult to engineer in firmware. The current LCD, which is shape-based from what I gather, is good insofar as it goes, but a high-resolution pixel-based replacement would be much better and a colour one even more so, if it can be achieved without sacrificing noticeable light transmission.
07-12-2016, 09:35 PM   #4
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I thought the actual crop factor depended on the sensor selected and was typically more like 1.53x for the K-3. Using that crop factor you will see that it is roughly 4800 pixels (and the 1.53 is rounded off really it is slightly larger).

07-12-2016, 09:57 PM   #5
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The number of pixels in crop mode isn't quite decided by Ricoh, because it belongs to the sensor read mode. When in crop mode, only the center portion of the sensor is read which allow a faster read (faster FPS). K1 crop mode has the same pixel size as the D800 DX crop mode = 4800x3200 . If the square mode was implemented, it couldn't be done with 6.5 FPS, but only a software feature. However, I guess x1.2 crop could be implemented since it is available on D800, but that's probably a marketing decision not to do it.
07-12-2016, 10:04 PM   #6
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I believe people were talking about a square crop mode in the prerelease versions of the K-1 that did;t make it to the release, but I don't have any sources for that at the moment.
07-12-2016, 10:55 PM   #7
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Lens are round (notwithstanding petal hoods). I never understood why sensors (and crop areas) couldn't be too.

However, I'd vote for a square crop option.
07-13-2016, 05:29 AM   #8
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Of course if you leave the camera in FF you can crop PP any dimensions you want: APS-C, vertical APS-C, Hasselblad/Rollei square, horizontal pseudo-panorama, classic romantic oval for facial portraits, diamond-shaped for baseball games, triangle for converging railroad tracks. Use your imagination!

07-13-2016, 05:40 AM - 2 Likes   #9
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My Fuji X10/X20 offer several crop modes and the square crop is usually my favorite. I was disappointed that they did not offer it on the K1.

My 90 year old Mom......in a Fuji crop. Looks great to me!
Name:  DSCF0005-800.jpg
Views: 372
Size:  738.0 KB

Regards!
07-13-2016, 06:30 AM   #10
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Other than frame rate what us the main benefit to alternate crop modes vs cropping in post?
07-13-2016, 06:32 AM   #11
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QuoteOriginally posted by Rupert Quote
My Fuji X10/X20 offer several crop modes and the square crop is usually my favorite. I was disappointed that they did not offer it on the K1.

My 90 year old Mom......in a Fuji crop. Looks great to me!
Attachment 317966

Regards!
By crikey, they didn't mix you up in the maternity hospital, did they?

Your mother's doing well (mine's 92, but not as upright as yours) she even makes your crop photos look good, Rupert!

Regards to you, too.
07-13-2016, 07:29 AM   #12
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QuoteOriginally posted by AstroDave Quote
More interestingly, however, it seems to me that another crop mode would be very nice to have: a "square" picture mode, on the order of 4900x4900 pixels. The width of this square would be about what Pentax is offering, and the height would fit just right into the full frame height of 4912 pixels.

Perhaps Pentax figures we are all so used to the standard (from 35mm film days!) 1.5:1 width to height ratio for images, that we don't want anything else. However, assuming that a normal APS-C lens produces uniform quality imaging in all directions (i.e. same height as width (actually round), even though we usually throw away the extra height resolution), the extra height pixels should have just as good image quality as the outer width pixels.
This would put you outside the APS-C image circle, don't just think width and height but consider the diagonal of your rectangles. 4900x4900 pixels on a k-1 is roughly a 24mm by 24mm square, which importantly has a diagonal of about 33.94mm. APS-C is 16x24mm rectangle, which is a diagonal of about 28.8mm, and that's as wide as an APS-C lens needs to cover. Add in shake reduction or composition adjust, and you might be moving well into a poor area of an aps-c lens.

Of course, many APS-C designated lenses would cover your proposed square just fine but I think Pentax likes to avoid built-in doohickies that might lead us into the danger zone..
07-13-2016, 08:47 AM   #13
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QuoteOriginally posted by BrianR Quote
This would put you outside the APS-C image circle, don't just think width and height but consider the diagonal of your rectangles. 4900x4900 pixels on a k-1 is roughly a 24mm by 24mm square, which importantly has a diagonal of about 33.94mm. APS-C is 16x24mm rectangle, which is a diagonal of about 28.8mm, and that's as wide as an APS-C lens needs to cover. Add in shake reduction or composition adjust, and you might be moving well into a poor area of an aps-c lens.

Of course, many APS-C designated lenses would cover your proposed square just fine but I think Pentax likes to avoid built-in doohickies that might lead us into the danger zone..
Yeah, I thought about that. Depends on what part of the frame one deems critical.

I like Paul the Sunman's comment above: lenses are round, so why aren't images round?!?!
07-13-2016, 09:28 AM   #14
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QuoteOriginally posted by leekil Quote
I believe people were talking about a square crop mode in the prerelease versions of the K-1 that did;t make it to the release, but I don't have any sources for that at the moment.

at around 0:40 you can see the guy selects a "1:1" crop mode.
07-13-2016, 09:24 PM   #15
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QuoteOriginally posted by UncleVanya Quote
Other than frame rate what us the main benefit to alternate crop modes vs cropping in post?
The LCD indicating the square frame in the viewfinder would be very useful in composing your shots.
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