How to quantify the quality of an enlarged image?

Posted by aidriiyan on Sep 15, 2010; 6:22am
URL: http://imagej.273.s1.nabble.com/How-to-quantify-the-quality-of-an-enlarged-image-tp3686914.html

Different study in image enlargement utilizes RMSE or PSNR to quantify if their image enlargement method is much better than the existing one.(lower RMSE and higher PSNR is better)

Questions
1. Why nearest-neighbor method in image enlargement produces significantly lower RMSE and higher PSNR than bilinear and bicubic even though the results of these two is much better than the nearest-neighbor?
2. Is it possible to create a better enlargement algorithm compared to n-n, bilinear and bicubic even though the RMSE is much larger and the PSNR is lower?

Can someone explain the concept of PSNR or RMSE in image processing and why I always get higher RMSE and low PSNR for my proposed method.

enlarged
original image :
n-n enlargement:
bilinear enlargement:
bicubic enlargement:
proposed method:

downscaled then upscaled
original image :
n-n enlargement:
bilinear enlargement:
bicubic enlargement:
proposed method: