Bug in ERGAS

[yc-cui]

🐛 Bug

It should be divided by the ratio, rather than multiplied by the ratio, otherwise it will amplify the correct indicator by the square of the ratio.

torchmetrics/src/torchmetrics/functional/image/ergas.py

Line 82 in ca7c8eb

ergas_score = 100 * ratio * torch.sqrt(torch.sum((rmse_per_band / mean_target) ** 2, dim=1) / c)

For reference, below is a correct implementation by matlab:

https://github.com/liangjiandeng/DLPan-Toolbox/blob/main/02-Test-toolbox-for-traditional-and-DL(Matlab)/Quality_Indices/ERGAS.m#L32

[github-actions]

Hi! thanks for your contribution!, great first issue!

[Mdmdma]

Hi this bug fix enables correct behavior, but now the documentation is not consistent with the source paper. In the source paper the ratio is <1 the way it is stated here it is supposed to be >1. I do not think this is a issue, but maybe noteworthy in the documentation.