how to set image size for scale 16:9

[hanjianfei]

No description provided.

[mayakraft]

1. Not sure if it's time to force-resize all images that don't meet 2:1 ratio and powers of 2 dimensions specs.
   resizing will change the input data (like should it resize nearest neighbor or bilinear filtering?). I like the wysiwyg or fail nature of it right now.

2. btw, in case you didn't catch it the easiest way to get up and running is to scale your image to 16:8, or 2:1 and make sure the pixel units are in powers of 2, like 2048x1024.