While probably most users would like to avoid upscaling, there's no way in EPSA Crop to prevent it (or foresee it happening).

The only indicator of the crop's size in relation to the original image is the size of the initial selection before applying manual crop.
When manually setting a crop, there's no indicator of how big the original image is. It might be 10 times bigger, or even smaller.
Therefore, it's hard/impossible to tell what the scaling will be.

It would be nice, if the cropping dialogue would show the resulting scaling factor for the selected crop.
Users could realize their selection will lead to upscaling (or scaling close around 1, which typically leads to blurry results too), and opt to change the crop, or knowingly accept the quality-loss.

So, i propose
1.
Add to the epsacrop-imagestyle effect: A checkbox "do not allow upscaling" (or a field "max. scaling factor").
2.
Show the resulting scaling factor on the cropping-UI.
2.a.
Some kind of alert (eg. red selection-border and a msg. "image will be upscaled") if the scaling factor gets bigger than 100%.
2.b.
A setting for the factor from which on the alert should be shown.
3.
a preview of the resulting crop, as seen on http://deepliquid.com/projects/Jcrop/demos.php?demo=thumbnail.
This would give a good impression of the resulting crop.

PS:
The Jcrop library used, has a feature "minSize" which could be used to prevent upscaling.

Comments

sirtet’s picture

Issue summary: View changes
sirtet’s picture

There's a patch that prevents upscaling on #1187670: Enforce minimum dimensions