Restrict width but unlimited height

Hi,

I’ve looked at your FAQ’s regarding setting a custom image size to either 0 or 9999 but this appears to only allow cropping proportionally to the original image.

Is it possible (for example)…

Original image is 1000 x 1000 pixels.

Crop image to (a defined) 400 pixels wide but be able to make the height anything I like within the original size. So I could choose 400×600 or 400×768.

Any thoughts?

Thanks.