Scale before processing
If you want the target image to be a percentage of its original size, then use
height=50%, or both. The parameter
scale is however a different story.
scale is used to scale the original image as a first step in processing the image. Applying
scale=25% will reduce the image before processing. This can produce some nice effects, or none, depending on what happens next.
This is how you use the
|Downsize to 10%
|Downsize to 5%
In both cases, the scaling is done as the first step in processing. In all cases the final image will have a width of 300px, so the scale parameter only affects the source image used prior resizing.