Negative BRISQUE value

[Genjo00]

Running the evaluation in the standard configuration from the terminal seems to return weird, too low values, sometimes even negative.

$ pyiqa brisque -t splatdiff_old/train/images/ --verbose
[2025-08-30 12:05:54] ===> Loading metrics: ['brisque']
[2025-08-30 12:05:56] ===> Metrics loaded: ['brisque']
[2025-08-30 12:05:57] Testing brisque with input splatdiff_old/train/images/diff_024.png: 100%|███| 25/25 [00:00<00:00, 40.63image/s]
{'brisque': {'mean': np.float64(0.16679931640625),
             'splatdiff_old/train/images/diff_000.png': 0.92010498046875,
             'splatdiff_old/train/images/diff_001.png': 0.71331787109375,
             'splatdiff_old/train/images/diff_002.png': -0.13128662109375,
             'splatdiff_old/train/images/diff_003.png': -0.30084228515625,
             'splatdiff_old/train/images/diff_004.png': 0.75604248046875,
             'splatdiff_old/train/images/diff_005.png': 2.06121826171875,
             'splatdiff_old/train/images/diff_006.png': -0.34796142578125,
             'splatdiff_old/train/images/diff_007.png': 0.30780029296875,
             'splatdiff_old/train/images/diff_008.png': 1.22735595703125,
             'splatdiff_old/train/images/diff_009.png': 1.55084228515625,
             'splatdiff_old/train/images/diff_010.png': 0.72918701171875,
             'splatdiff_old/train/images/diff_011.png': 0.95697021484375,
             'splatdiff_old/train/images/diff_012.png': 0.13433837890625,
             'splatdiff_old/train/images/diff_013.png': 0.98419189453125,
             'splatdiff_old/train/images/diff_014.png': 1.60638427734375,
             'splatdiff_old/train/images/diff_015.png': 1.95208740234375,
             'splatdiff_old/train/images/diff_016.png': -0.24822998046875,
             'splatdiff_old/train/images/diff_017.png': -0.88580322265625,
             'splatdiff_old/train/images/diff_018.png': -0.49822998046875,
             'splatdiff_old/train/images/diff_019.png': 0.04608154296875,
             'splatdiff_old/train/images/diff_020.png': -2.14801025390625,
             'splatdiff_old/train/images/diff_021.png': -0.46319580078125,
             'splatdiff_old/train/images/diff_022.png': -1.53717041015625,
             'splatdiff_old/train/images/diff_023.png': -1.70635986328125,
             'splatdiff_old/train/images/diff_024.png': -1.50885009765625}}

I'm running pyiqa 0.1.14.1
Attached is diff_020.png for reference

[Genjo00]

I looked a little into this, and it seems that this is a known and documented limitation of BRISQUE, it might still be better to clamp the values between 0 and 100.