Crop Transformation

[Marpel]

Hello,

I am having problems with the Crop Transformation and am sure it is partly due to my lack of knowledge. However, I am confused by the following:

- Why can I not enter numbers in the size box? I am trying to do crop sizes to a specific pixel dimension and find moving the outline too inexact. For what I am doing, the location of the crop is less important than the exact dimensions and they need to be to the exact pixel value. So, if I wanted a 1000 X 1000 pixel sized crop, would it not be easier to just enter those numbers in the size boxes? As indicated above, it may be possible but I can't figure out how. This would be also far easier than trying to calculate the margins for a 1234 X 1243 crop in a 6048 X 4032 image, as an example.

- Why can't the margins be used in other than "Arbitrary"? If I set it to "Square" or other, the margins grey out and are not accessible.

- When I have a crop size that I wish, if I click on the centre + to move the outline to another location in the image (just click, no movement), the size numbers change by up to four pixels. The most bizarre aspect of this is if the shape is set to "Square", and I click to move the outline, it regularly changes the size to something other than a square. For example, I had a square 1195 X 1195 and when I clicked to move it, the size changed to 1196 X 1191. These new numbers stayed even after I had moved the outline. I have tried multiple times to do this and be very accurate about where I place the cursor prior to clicking, to no avail.

Thanks in advance for any help you can offer.

Marv

[jsachs]

You can enter numbers into the margins and borders fields, but you have to do it fast enough. There is a time delay and if you do not enter a digit within that time the transformation recalculates to reflect the new values.

There are some roundoff issues when enforcing the aspect ratio that can produce small changes in the size of the crop box.

[Marpel]

Thanks Jonathan. I was noticing the time requirement for entering numbers into the margins and borders, especially when I was slow when entering.

Regarding your comment re "some roundoff issues", is that related to the crop outline always "snapping to" the center of a pixel?? I observed, when zoomed in to see the crop outline and individual pixels, that the outline would only line up in the middle of a pixel, rather than the boundary between two pixels (where I would have expected it to line up with my layman's level of competence), regardless of how the outline was moved. It seems, when the crop transform is complete, the resulting image boundary, especially at the bottom left corner, is over by half a pixel to where the crop outline was. And, by referring to it as "issues", does that suggest it is an unwelcome thing and will eventually be changed so the outline passes between two adjacent pixels and the pixel size will remain accurate if the outline is moved around within the image??

Marv

[jsachs]

The crop transformation does not work on fractional pixels. To do so would require resampling the input image which would be much slower and would blur the image slightly.