Screenshot of GrafX2 with a picture by Tomic (that you can barely see, as there is a window above it). The window shows the "smooth" effect configuration where several 3x3 blur matrices can be selected, or custom valaes can beentered manually
https://mastodon.tetaneutral.net/system/media_attachments/files/112/348/370/730/861/713/original/6eccbdcbbd7fb185.png