To change the image size to fit in given width and height while retaining original proportions, specify the width and height parameters (w and h in URLs) while setting the crop parameter to fit (c_fit in URLs).

When using the 'fit' crop mode, all original image parts are visible. Both width and height dimensions of the transformed image must not exceed the specified width & height. However, they may be smaller than the specified values in order to keep the original proportion.

Here's an original image:

Here's how to make the image fit within 70x90 boundaries:

Note that the result image is actually 70x47 in order to keep the original proportions of 864x567 (~1.5).

Here's an example of fitting the original image to 300x100, which will generate a 150x100 image (retaining the 1.5 aspect ratio):

The 'fit' crop mode can be applied on overlays as well:

Note that the fit crop mode enlarges the image when requesting larger width and height than the original image's dimensions. For example (original is 912x608):