Composite artifact colors
[8][9] Depending on the exact PAL system used results will vary (if PAL-M or PAL-N are used, color artifacts similar to NTSC might be possible).
Blurring is a general effect of using a composite connection, that simply creates new colors due to a mix of adjacent horizontal pixel values.
Nevertheless, this effect can be exploited by using dither patterns, generating new intermediate palette colors[10] on machines with a sufficiently high resolution display, like the ZX Spectrum,[11] Mega Drive/Genesis,[12][13] NES/Famicom[14] or Amiga.
[15] Computers such as the Apple II[16] and the CGA[17][18] video card for the IBM PC, output a signal that is an approximation of the broadcast standard.
For a broadcast-quality signal, that would mean 910 pixel cycles per each line (as opposed to 858 as later standardized by the ITU-R Recommendation BT.601), with about 750 of them occupying the visible portion of the screen.
This effect was exploited by game artists on some machines (specially those capable of generating higher resolution graphics but having a limited color palette) through the use of dithering patterns.
[11][12][13][14][22][23] When using IBM's Color Graphics Adapter (CGA) with a NTSC TV as a composite monitor, the separation between luminance and chrominance is imperfect, yielding cross-color artifacts.
It is not possible to reliably display 256 dots across the screen due to the limitations of the NTSC signal and the phase relationship between the graphics chip clock and colorburst frequency.
The graphics chip internally can power up on either the rising or falling edge of the clock, so the bit patterns that represent orange and blue are not predictable.
Most CoCo games start with a title screen and asks the user to press the reset button until the colors are correct.
[32] The coarse, low-resolution graphics display mode works differently, as it can output a pattern of dots per pixel to offer more color options.
[34][35] Graphics 8 mode on early Atari 8-bit computers with the Color Television Interface Adaptor (CTIA) chip displayed black or white images at a resolution of 320×192.
[1] Games such as Lode Runner, Flight Simulator II, and the Ultima series took advantage of this effect to display extra colors.
[37] When Atari began shipping computers with the improved Graphic Television Interface Adaptor (GTIA), users found that such programs displayed incorrect colors and required an updated version of the software.
[38] In fact, artifact colors were inconsistent across the entire Atari 8-bit product line complicating playfield design but only affected a handful of titles that used this graphics mode.
For some undocumented reason known only to Atari, they did not enable the chroma pin on the monitor jack of the 800XL although several modifications have been published to incorporate this support.
Home computers like the Atari ST also have graphics prepared with dithering techniques to take advantage of composite TV connections.
The Mega Drive/Genesis takes advantage of composite video horizontal blurring of vertical dither patterns to simulate transparency effects on many games.
[41] The Commodore Amiga, when connected over composite video, suffered from noticeable horizonal blurring, specially affecting colored pixels and smoothing out dithered transitions.
Pixel artist Henk Nieborg mentions using dithering on the 1992 Amiga game Lionheart in order to create additional colors.
[40] The special Hold-And-Modify is particularly suited for displaying "high color" TV-like images, taking full advantage of horizontal blurring.
The ZX Spectrum resolution is high enough to allow the generation of artifact colors, but the effect was not explored during its commercial lifetime.
