PPU palettes: Difference between revisions
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=== RGB PPU palettes === | === RGB PPU palettes === | ||
The 2C03, 2C04, and 2C05 all output RGBS, with each of the three video channels using a 3-bit DAC. | The 2C03, 2C04, and 2C05 all output RGBS, with each of the three video channels using a 3-bit DAC. Their look-up tables (one digit for each of red, green, and blue, in order) are given below: | ||
==== 2C03 and 2C05 ==== | ==== 2C03 and 2C05 ==== | ||
This palette is intentionally similar to the NES's standard palette, but notably is missing the greys in entries $2D and $3D. | This palette is intentionally similar to the NES's standard palette, but notably is missing the greys in entries $2D and $3D. |
Revision as of 20:17, 29 October 2014
Memory Map
The palette for the background runs from VRAM $3F00 to $3F0F; the palette for the sprites runs from $3F10 to $3F1F. Each color takes up one byte.
Address | Purpose |
---|---|
$3F00 | Universal background color |
$3F01-$3F03 | Background palette 0 |
$3F05-$3F07 | Background palette 1 |
$3F09-$3F0B | Background palette 2 |
$3F0D-$3F0F | Background palette 3 |
$3F11-$3F13 | Sprite palette 0 |
$3F15-$3F17 | Sprite palette 1 |
$3F19-$3F1B | Sprite palette 2 |
$3F1D-$3F1F | Sprite palette 3 |
Each palette has three colors. Each 16x16 pixel area of the background can use the backdrop color and the three colors from one of the four background palettes. The choice of palette for each 16x16 pixel area is controlled by bits in the attribute table at the end of each nametable. Each sprite can use the three colors from one of the sprite palettes. The choice of palette is in attribute 2 of each sprite (see PPU OAM).
Addresses $3F04/$3F08/$3F0C can contain unique data, though these values are not used by the PPU when normally rendering (since the pattern values that would otherwise select those cells select the backdrop color instead). They can still be shown using the background palette hack, explained below.
Addresses $3F10/$3F14/$3F18/$3F1C are mirrors of $3F00/$3F04/$3F08/$3F0C. Note that this goes for writing as well as reading. A symptom of not having implemented this correctly in an emulator is the sky being black in Super Mario Bros., which writes the backdrop color through $3F10.
Thus, indices into the palette are formed as follows:
43210 ||||| |||++- Pixel value from tile data |++--- Palette number from attribute table or OAM +----- Background/Sprite select
As in some second-generation game consoles, values in the NES palette are based on hue and brightness:
76543210 |||||||| ||||++++- Hue (phase, determines NTSC/PAL chroma) ||++----- Value (voltage, determines NTSC/PAL luma) ++------- Unimplemented, reads back as 0
Hue $0 is light gray, $1-$C are blue to red to green to cyan, $D is dark gray, and $E-$F are mirrors of $1D (black). The canonical code for "black" is $0F or $1D. $0D should not be used; it results in a "blacker than black" signal that may cause problems for some TVs. It works this way because of the way colors are represented in an NTSC or PAL signal, with the phase of a color subcarrier controlling the hue. For details, see NTSC video.
The 2C03 RGB PPU used in the PlayChoice-10 and Famicom Titler renders hue $D as black, not dark gray. The 2C04 PPUs used in many Vs. System arcade games have completely different palettes as a copy protection measure.
RGB PPU palettes
The 2C03, 2C04, and 2C05 all output RGBS, with each of the three video channels using a 3-bit DAC. Their look-up tables (one digit for each of red, green, and blue, in order) are given below:
2C03 and 2C05
This palette is intentionally similar to the NES's standard palette, but notably is missing the greys in entries $2D and $3D.
333,014,006,326,403,503,510,420,320,120,031,040,022,000,000,000 555,036,027,407,507,704,700,630,430,140,040,053,044,000,000,000 777,357,447,637,707,737,740,750,660,360,070,276,077,000,000,000 777,567,657,757,747,755,764,772,773,572,473,276,467,000,000,000
2C04
All four 2C04 PPUs contain the same master palette, but in different permutations. This image shows all the colors except the six shades of grey:
RP2C04-0001
755,637,700,447,044,120,222,704,777,333,750,503,403,660,320,777 357,653,310,360,467,657,764,027,760,276,000,200,666,444,707,014 003,567,757,070,077,022,053,507,000,420,747,510,407,006,740,000 000,140,555,031,572,326,770,630,020,036,040,111,773,737,430,473
RP2C04-0002
000,750,430,572,473,737,044,567,700,407,773,747,777,637,467,040 020,357,510,666,053,360,200,447,222,707,003,276,657,320,000,326 403,764,740,757,036,310,555,006,507,760,333,120,027,000,660,777 653,111,070,630,022,014,704,140,000,077,420,770,755,503,031,444
RP2C04-0003
507,737,473,555,040,777,567,120,014,000,764,320,704,666,653,467 447,044,503,027,140,430,630,053,333,326,000,006,700,510,747,755 637,020,003,770,111,750,740,777,360,403,357,707,036,444,000,310 077,200,572,757,420,070,660,222,031,000,657,773,407,276,760,022
RP2C04-0004
430,326,044,660,000,755,014,630,555,310,070,003,764,770,040,572 737,200,027,747,000,222,510,740,653,053,447,140,403,000,473,357 503,031,420,006,407,507,333,704,022,666,036,020,111,773,444,707 757,777,320,700,760,276,777,467,000,750,637,567,360,657,077,120
Backdrop color (palette index 0) uses
During forced blanking, when neither background nor sprites are enabled in PPUMASK ($2001), the picture will show the backdrop color. If only the background or sprites are disabled, or if the left 8 pixels are clipped off, the PPU continues its normal video memory access pattern but uses the backdrop color for anything disabled.
The background palette hack
If the current VRAM address points in the range $3F00-$3FFF during forced blanking, the color indicated by this palette location will be shown on screen instead of the backdrop color. (Looking at the relevant circuitry in Visual 2C02, this is an intentional feature of the PPU and not merely a side effect of how rendering works.) This can be used to display colors from the normally unused $3F04/$3F08/$3F0C palette locations. A loop that fills the palette will cause each color in turn to be shown on the screen, so to avoid horizontal rainbow bar glitches while loading the palette, wait for a real vertical blank first using an NMI technique.
RGB palette values
The NES does not generate RGB video. Using this table will result in video that looks more like a PlayChoice than like an NES, and some games will look graphically sterile if quirks of the NES's video output are not emulated. However, sometimes people want something quick, dirty, and functional before they bother with adding correct NTSC video decoding, or they're making an emulator for a low-end device that cannot decode NTSC video in real time. In a predefined palette, each sRGB triplet represents the color that results from decoding a large flat area with a given palette value.
The following table was generated using blargg's Full Palette demo on Nestopia:
84 84 84 0 30 116 8 16 144 48 0 136 68 0 100 92 0 48 84 4 0 60 24 0 32 42 0 8 58 0 0 64 0 0 60 0 0 50 60 0 0 0 152 150 152 8 76 196 48 50 236 92 30 228 136 20 176 160 20 100 152 34 32 120 60 0 84 90 0 40 114 0 8 124 0 0 118 40 0 102 120 0 0 0 236 238 236 76 154 236 120 124 236 176 98 236 228 84 236 236 88 180 236 106 100 212 136 32 160 170 0 116 196 0 76 208 32 56 204 108 56 180 204 60 60 60 236 238 236 168 204 236 188 188 236 212 178 236 236 174 236 236 174 212 236 180 176 228 196 144 204 210 120 180 222 120 168 226 144 152 226 180 160 214 228 160 162 160
Other tools for generating a palette include one by Bisqwit and one by Drag.