Reported V4.25: custom crop is inaccurate

[irfanfan]

I saw a previous bug submission for the same issue for v4.23, which was marked as FIXED, but it's not fixed. I have been using custom crop in Irfanview with the same camera for years and did not encounter this issue.

How to reproduce:

OS: windows xp sp3
monitor resolution: 1024x768
irfanview: v4.25

zoom mode: fit images to desktop. (this results in 43% zoom for me)
start with JPG from canon digital camera 2048x1536 (4:3 ratio)
shift+C to custom crop
set offset = (0,0), width = 1600, height = 1200
result is the selection window size is 1599x1200
And if I do shift+C again, the width and height are pre-populated to 1599x1199. So something weird is going on.

I saw in the other thread people suggested using 100% zoom mode. While that does leave the selection window at 1600x1200, it's useless because I can't seeing the entire image to see what I'm cropping.

Another person suggested that using a fixed zoom would be a workaround. But this issue still occurs when I used fixed zoom of 33%.

[Bhikkhu Pesala]

Another person suggested that using a fixed zoom would be a workaround. But this issue still occurs when I used fixed zoom of 33%.

A fixed zoom step of 10% works fine for me. Try absolute values if that doesn't work.

[irfanfan]

OK, I did more investigation into the zoom issue. I arrived at some additional conclusions:

Previously, I had it set to zoom step 10%, absolute step. With 1024x768 display and Fit Images to Desktop, the zoom was set to 43%. Custom crop was failing. When I zoomed out once, which made the zoom 33%, custom crop still failed. Now I have a guess why. When the zoom showed 43%, it wasn't exactly 43.00%, it was probably something like 43.17%. So the math was causing rounding error with the custom crop. And when I reduced zoom by 10% absolute, it wasn't exactly 33%, it was something like 33.17%, which still caused math rounding errors.

When I set my zoom setting to "Fixed Values" (which ignores step), then zoomed out to 33%, now the custom crop works well, because it is probably 33.00% exactly.

So this workaround works if you set zoom setting to Fixed Values. But I think this is still a bug.