Image resizing is pretty complicated with regards to quality.I intend to compare difference in quality with metrics such as SSIM, butteraugli , ssimulacra and others to get an overview of the different image resize techniques.However i need to have a reference image to compare with the resized image.I think lossless video sources at different quality levels can provide me with the reference images.
I download the sintel lossless trailer png images for 480p and 720p.Then i tried to downsample a 720p frame to its 480p equivalent.
The problem that i am not able to downsample get to exact dimension of the 480p without messing up the aspect ratio. I tried with both Imagemagick and photoshop.
Could someone help me downsample the image in such a way so as to produce a more or less accurate version of the 480p frame from the 720p frame
convert sintel_trailer_2k_0160_720p.png -resize 854x480\! sintel_trailer_2k_0160_resize.png