LionKinEn's comic, grabbed from artist's Patreon (this one's for free), the original pic resolution was quite small(around 1000×1400), latest Real-ESRGAN image restoration model was used to upscale (4.0x, as the training model was designed for) and restore (denoise, remove JPEG artifacts) the image.
All uploaded pics were compressed with lossless PNG format (level 9 compression).