No, you didn't understand me, sorry. I understood it just fine, but didn't explain myself well enough. The relative contrast at the point of curvature causes a

No, you didn't understand me, sorry. I understood it just fine, but didn't explain myself well enough. The relative contrast at the point of curvature causes an aliasing effect in the brain where the line colors are (depending on the color) added to or subtracted from the gray value. In effect this causes an apparent sharpening of the curve. However, on those lines where the transition takes place on the straight portion of the wave, no such aliasing takes place because there is no curvature. It's like anti-aliasing in reverse.