Many older/commercial video codecs optimized for PSNR, which results in the output being blurry and textureless because that's the best way to minimize rate for the same PSNR.
Even with that, showing H.265 having lower PSNR than H.264 is odd --- it's the former which has often looked blurrier to me.
It checks a reference video against an encoded video and returns a score representing how close the encoded video appears to the original from a human perspective.
also see https://jon-cld.s3.amazonaws.com/test/ahall_of_fshame_SSIMUL... which is an ab comparison of a lot of images where it gives 2 versions, one preferred by ssimulacra, the other preferred by vmaf
TID2013 for example is an image dataset with many artifacts completely unrelated to compression and scaling.
- Additive Gaussian noise - Additive noise in color components is more intensive than additive noise in the luminance component - Spatially correlated noise - Masked noise - High frequency noise - Impulse noise - Quantization noise - Gaussian blur - Image denoising - JPEG compression - JPEG2000 compression - JPEG transmission errors - JPEG2000 transmission errors - Non eccentricity pattern noise - Local block-wise distortions of different intensity - Mean shift (intensity shift) - Contrast change - Change of color saturation - Multiplicative Gaussian noise - Comfort noise - Lossy compression of noisy images - Image color quantization with dither - Chromatic aberrations - Sparse sampling and reconstruction
Doing better on TID2013 is not really an indication of doing better on a video compression and scaling dataset (or being more useful for making decisions for video compression and streaming).