Hello again. Sorry for this question, probably this subject has already been covered elsewhere, but I really don't know where to start. What do you call that visual effect that appears on some PSX games that renders a grid-like pattern all over the screen? For instance, compare Alien Trilogy on the Saturn and on the Playstation to see what I mean. It looks like a dot-hole-filter which, IMHO, doesn't look nice at all. (Another example is Silent Hill where it shows as a star or cross like pattern.) Although the Saturn version lacks the lighting effects of the PSX I find the Saturn version more pleasing because of the absence of that nasty effect, rendering crisper graphics. When I use the same game with the PS2, that same effect is present, and I think it looks a lot worse! Only if I turn texture smoothing ON it gets acceptable... Is this a hardware feature (on the PSX), which in turn is emulated on the PS2' psx driver? Would it be possible to disable this effect, via hardware or software?
Not completely sure but could be the ps1 32 bit RISC cpu. The ps2 integrated this into its hardware so when u try to play a ps1 game on the ps2, it switches circuitry to the ps1 cpu and locks out the ps2 side. It must be a way the games are written to utilise the cpu abilities. https://en.m.wikipedia.org/wiki/R3000 Here is some info on the chip. If u compare it to the Saturn 32bit RISC cpu, maybe that will give u some clues. The only way this effect could be turned off would be on a pc through emulation.
It's dithering - it's an intentional feature of the PlayStation GPU, although one that's under programmer control. It's been a while, but I think it's bit 9 in the draw mode setting register. If this bit is set, then the 24 bit source color is dithered to 5:5:5 RGB over a 16 pixel (4x4) cell, and if it's clear then it's sent directly (basically, just ignoring the 3 LSBs of each component). Most 3D titles had it turned on, because just clipping the color values tended to give you very bad banding on anything with smooth shading, and since back in '95 most people were using composite connections the TV tended to smooth out the dither anyway. You could possibly patch a game to disable it - you would just have to find every write to that register and change the value written.
TriMesh is correct: bit 9 in a DR_MODE, DR_PAGE, or similar primitive will enable dither for all the following primitives that don't reset it (polygons don't count for reset, apparently). Globally you can turn it on by setting DRAWENV.dtd to 1. Personally I wouldn't suggest ever disabling this for 3D models. The shading looks pretty much horrible without any dithering to fill the visual gaps of gradients on RGB555.
Thanks for the suggestion. Although I would not know how to do it , I find the idea very attractive. Hmmmm, a game version with dithering on and another with dithering off... Incidentally, this means the Saturn cannot do dithering and that PSX games (which use dithering) don't look so good on the PS2...?
My technical knowledge of the Saturn is quite limited, but some people online do mention dithering when talking about the Saturn. However the video hardware in the Saturn is a terribly bad design and even if it can do it, there might be circumstances when it doesn't work or is too slow to be usable. People make a big deal about Saturn games with transparency because the video hardware makes it near impossible to use it for anything useful. The PS2 isn't really that accurate at running PS1 games, I believe the rendering is done with a combination of EE+GS while IOP runs the game code. So don't expect pixel accurate rendering.
