Author Topic: Video Specifications  (Read 11009 times)

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Offline RT 55J

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Video Specifications
« on: February 10, 2009, 09:58:30 am »
NOTE: Do not post in this topic unless you are offering accurate technical specifications. If you have a correction, do it in another thread.

Nintendo Entertainment System

Display Resolution:

- 256 pixels wide by 240 pixels tall.

- Most NTSC TVs (and emulators) crop off the top and bottom 8 rows of pixels.

- Many games crop off the 8 leftmost columns of pixels.


- The NES has a palette of approximately 52 colors.

- From these colors, the NES can make 8 palletes.

-- 4 palettes for the background layer and 4 for the sprites

-- Each palette has 4 colors, with each palette sharing the same transparent background color.

- The NES supports emphasizing red, green, and blue colors as well as switching to monochrome, but very few commercially release games took advantage of this (they could've done some sweet pseudo-transparency effects :( ).


- Tiles are 8 by 8 pixels, with each pixel being represented by 2 bits, thus allowing 4 colors (2^2) per pixels.

- There are 512 tiles total: 256 for the background and 256 for sprites.


- The maximum amount of sprites onscreen is 64.

- The maximum amount of sprites per scanline is 8

- Sprites can be flipped vertically and horizontally.

- Sprites can either be 8 or 16 pixels tall.

-- Note: This is a global setting. You cannot have 8 and 16 pixel tall sprites onscreen at the same time.

-- In 8x16 sprite mode the game can use sprite and background tiles. This is accomplished by sacrificing the last bit of the "tile number" for the 8x8 sprite mode.

--- Note: Tiles in the 8x16 sprite mode cannot be selected independently. The ID of the second tile is always the one directly after the first.


(I'll get to that later. My class is about to start. :P )


"its a good day to do what has to be done by me and help my brother to defeat the enemys" - John Freeman

Offline Maxim

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RE: Video Specifications
« Reply #1 on: February 16, 2009, 08:18:53 am »
Sega Master System

Recommended emulator: Meka

Resolution: 256x192*. Horizontal scrolling will usually cut that down to 248x192.

Colours: up to 32 on-screen* with 64 possible values. Most games will use 16 for the background and 16 for sprites.

Tiles: 8x8 pixels. There can be up to 450 or so shared between background and sprites. They may be updated on the fly.

Background tiles can be flipped and mirrored. Sprites can't. Any tile can use up to 16 colours from one of two palettes - again, generally one palette is for the background and one is for sprites.

The SMS uses dedicated video RAM so graphics are generally stored compressed in the ROM, except sprites which are streamed from the ROM to video RAM, and are stored uncompressed for speed.

Layers: There are no "real" layers, but there are effectively three: the background, the sprites, and the "foreground", which is simply background tiles where 15 of the 16 colours are drawn over the top of any sprites.

Sprites: maximum 8 per scanline, maximum 64*. There are possibilities for 8x16 sprites and 2x zoomed sprites but they don't affect mapping.

Raster FX: things that can be changed mid-frame are:

- horizontal scrolling

- colours

- name table

Things that can be, but generally aren't, changed mid-frame are:

- sprites

- video mode

* except for a few special cases

Sega Game Gear

The Game Gear is exactly the same as the Master System except:

1. It chooses 32 colours from 4096 possible values instead of 64.

2. Its screen shows only the central 160x144 area of the Master System's screen

The latter means you can often screengrab the "tilemap view", or use a "disable GG crop" emulator option, to grab the off-screen area. This often contains garbage, though.

Some Game Gear games are Master System games running in its backwards compatibility mode. On the original system this meant some (ugly) scaling of the screen to fit into the available LCD pixels. This doesn't affect mapping, emulators play those games as Master System games.

Offline TerraEsperZ

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RE: Video Specifications
« Reply #2 on: March 11, 2009, 08:05:56 pm »
Does anyone have any idea how the GBA handles transparencies? By that, I mean the exact process it uses to calculate the resulting pixel colour based on the background pixel and the transparent one, if there are more than one blend mode or whatever.

I'm asking this because I've been attempting to replicate a map where there is transparent water over a parallax background in Paint Shop Pro, and I'm simply unable to come up with colours that are even close to the original. A simple transparent layer doesn't cut it, no matter the opacity, so I'm guessing there are some tricks going on with individual colour channel bit value and palette restriction or something like that.


Current projects: Bucky O'Hare (NES), Metal Storm (NES), Clock Tower (SNES), Ristar-The Shooting Star (Gen), Sonic The Hedgehog (Gen), Sonic CD (Sega CD), Mega Man Zero (GBA), Battletoads (NES)
Current project that are on hold because job burnout :
-Drill Dozer (GBA)
-Sonic 3D Blast (Genesis)
-Naya's Quest (PC)

Offline Maxim

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RE: Video Specifications
« Reply #3 on: March 12, 2009, 03:28:49 am »
According to <link>>/link>, there's a register determining the blend mode (BLDALPHA) which I'm pretty sure is more complicated than a simple layer blend. You might get close with additive blending and then messing with the slider, but I can't figure out an exact formula (and you don't know what's in that register anyway).