Colour emphasis
Colour emphasis on the NES is accomplished via bits 5, 6, and 7 of PPUMASK, for red, green, and blue respectively. These bits enable/disable an “emphasis” or “tint” effect visually on screen.
- Bit 5 emphasizes red on the NTSC PPU, and green on the PAL & Dendy PPUs.
- Bit 6 emphasizes green on the NTSC PPU, and red on the PAL & Dendy PPUs.
- Bit 7 emphasizes blue on the NTSC, PAL, & Dendy PPUs.
- Each bit emphasizes 1 color while darkening the other two. Setting all three emphasis bits will darken colors $00-$0D, $10-$1D, $20-$2D, and $30-$3D (see PPU palettes). Note that $1D black is affected by color emphasis, but $0F black is not.
- The emphasis bits are applied independently of greyscale (bit 0 of PPUMASK), so they will still tint the color of the grey image.
On Dendy and PAL PPUs, the purpose of bits 5 and 6 are reversed (red for green, and green for red).[1][2]
See NTSC video for a description of how bits 5-7 work on NTSC and PAL PPUs.
The RGB PPU used by the Vs. System, PlayChoice-10, and some other systems treat the emphasis bits differently. Instead of darkening other RGB components, it forces one component to maximum brightness. A few games, which set all three tint bits to darken all colors, are unplayable on these PPUs because they instead turn the entire screen white.
- NTSC video
- PPU palettes
- PPU registers
- Colour-emphasis games
- Color $0D games
- Talk:Myths#All_three_color_emphasis_bits_with_color_0D
- ↑ PAL PPU swaps green and red emphasis bits: http://forums.nesdev.org/viewtopic.php?p=131889#p13188
- ↑ Dendy PPU swaps green and red emphasis bits: http://forums.nesdev.org/viewtopic.php?p=155513#p155513