Weird Crop Behavior

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Weird Crop Behavior

Postby NNN635125362728450134 » Tue Dec 04, 2018 6:39 am

I am having a problem with cropping that is new. When I hit the Crop button, the crop seems to be set automatically somewhat smaller than the actual image size. I can't then drag a line around the area I want to crop. I have to grab a corner from the pre-existing crop that it defaults to to change size.

Any idea why this is a happening and how to fix? Thanks.
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Re: Weird Crop Behavior

Postby Ian3 » Tue Dec 04, 2018 8:11 am

Probably the result of a lens correction applied on import. Find an image where that happens, go to the lens corrections, and turn them off and see whether that changes it for that image. If so you can (if you choose) turn off auto lens correction on import. But I’m only on my iPad at the moment so I can’t immediately check the exact steps to do that.

Ian
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Re: Weird Crop Behavior

Postby Tonyh-s » Tue Dec 04, 2018 9:15 am

I sometimes get the same thing. What I have noticed is that the crop is 6000 x 4000 (I set the crop to original) but the actual photo shown on the screen is something like 6030 x 40020. I don't know what is going on as the camera only gives 6000 x 4000 pixel images.

Not a lot of help I know, but just to let you know that you are not alone :-)
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Re: Weird Crop Behavior

Postby Ian3 » Tue Dec 04, 2018 9:41 am

Now that I'm at a proper computer, I can check how you change this. On the Lens Correction tool, click the ... (on the same line as the Lens Correction title) then choose Disable default lens correction. This will stop the lens correction being automatically applied on import, but it won't change it for already imported images. BUT if you want the lens correction you may not want to do this by default.

I think what happens is that lens correction involves shifting pixels around, so that, for example, with pincushion distortion, pixels get shifted towards the edge of the frame, and of course some of them move outside the edge of the rectangle. For some lenses, if you turn the lens correction off, you will see that the pixels recorded by the sensor do not form a straight-edged rectangle.

The amount of overlap at the edges depends on the camera, the lens and the focal length. On one pocket camera I have (Canon S110) the real focal length at the widest zoom ("24mm equivalent") is only actually 5.2 mm, and the uncorrected distortion is gross. It is instructive to shoot RAW + JPG with it and compare the out of camera JPG with the uncorrected RAW. The camera is applying a huge amount of correction to produce the JPG. On the other hand with different cameras and longer focal lengths, I don't see any pixels outside the crop area.

My usual approach is to let C1 apply its correction. Just occasionally, when I have been unable to get quite a wide enough angle for my scene, I turn off the correction to gain a few pixels. But that is only good if there is nothing in the scene that will look bad as a result - a curved "straight" wall, for instance.

Ian
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Re: Weird Crop Behavior

Postby NNN635125362728450134 » Wed Dec 05, 2018 4:00 am

Thanks Ian3. That was it! I was using a zoom lens and apparently the correction only affects the crop at wider angles of the zoom, so it seemed kind-of random.

Thanks again.
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Re: Weird Crop Behavior

Postby Ian3 » Wed Dec 05, 2018 8:58 am

NNN635125362728450134 wrote:Thanks Ian3. That was it! I was using a zoom lens and apparently the correction only affects the crop at wider angles of the zoom, so it seemed kind-of random.

Thanks again.

Yes it tends to be the wide end that needs correction more. I have lenses where I see exactly the same.

Ian
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