First-pass image compression: test a hard image

Before compressing a batch, choose one image with fine text, gradients, or transparent edges. Apply the intended settings to a copy and compare output size and visible quality with the original. Check the actual export in a second viewer. If artifacts are unacceptable, change the format or setting before processing the rest. Preserve all originals, since recompressing already degraded outputs compounds quality loss. One representative test defines a starting method, not a guarantee for every image.