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51 lines
2.2 KiB
Text
51 lines
2.2 KiB
Text
TV pass or fail?
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This program is designed for NES and tests various aspects of the
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display it is connected to. Press the A Button to switch screens.
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_____________________________________________________________________
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NTSC chroma/luma crosstalk
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The PPU in the PlayChoice arcade system generates RGB video, with
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red, green, and blue color information on separate cables.
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The PPU in the NES generates composite video, with chroma (color)
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and luma (brightness) information carried on one cable at different
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frequency bands. To keep the circuit cheap, it does not perform
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proper filtering to keep the chroma from bleeding into the luma.
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This especially has an effect on 45 degree diagonal lines. But an
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accurate emulator must preserve the same artifacts, as games such as
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Blaster Master rely on them to create the richest color palette.
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This screen displays something noticeably different on an NTSC NES
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PPU vs. the RGB PPU that most PC based NES emulators emulate.
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Display on RGB system: Display on NTSC system:
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,---------. ,---------.
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| ===== | | ===== |
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|%%%%%%%%%| | PASS! |
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| | | |
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| PRESS A | | PRESS A |
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`---------' `---------'
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_____________________________________________________________________
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Pixel aspect ratio
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PC displays most commonly generate square pixels. A square pixel
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on an NTSC display is 7/12 of a chroma cycle wide, but the NES PPU
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did not generate square pixels. Instead, it generated pixels 8/12
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of a chroma cycle wide, which are somewhat wider than they are tall.
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This made games' graphics appear stretched. If they are displayed
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with square pixels on a PC based emulator, graphics will not appear
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with the intended proportions.
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This screen shows three rectangles. One is a square on NTSC NES
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and PlayChoice, one is a square on PAL NES, and one is a square
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with square pixels.
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_____________________________________________________________________
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Legal
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Copyright 2007 Damian Yerrick
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Do not distribute this quick and dirty preview version to the public
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until it has been tested on an NES.
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