4 ms·

If you had a plain old monitor of TV resolution, then going to so called "high res" (640x512) meant that there was a terrible flickering that made this unusable

by avel 7y ago

If you had a plain old monitor of TV resolution, then going to so called "high res" (640x512) meant that there was a terrible flickering that made this unusable. You had to buy an expensive multiscan monitor that could handle that. A trick I used to do was to jump up to the NTSC equivalent (640x400) which was flickering less in my standard monitor.

snvzz 7y ago
>"high res" (640x512) In OCS Amiga, Low/High/SuperHigh are defined by the base (as in not using overscan) Horizontal resolution, 320/640/1280. PAL and NTSC are 256 and 200 lines base vertical resolution respectively, and 50/60Hz vertical refresh rate respectively. 512 and 400 lines are Interlaced modes. The flickering has to do with the interlacing. The improvement perceived with the NTSC mode is due to the increased vertical refresh rate. ECS Amiga (A500+/A600/A3000) introduces the so-called Productivity modes, which are just the 512/400 lines hires modes but in Progressive, thus doubling the horizontal refresh rate to ~31KHz, while also doubling the DMA bandwidth required. At full DMA you can form a a palette of 2^2 colors instead of the usual hires 2^4, and unless you have FAST RAM you'll want to keep it at 2 color in order to let the CPU use the odd ram access cycles. This palette can of course be changed during horizontal blanking, as then the display DMAs are off and the copper has room to access the palette registers, or several times midline if only using 2 colors. In Productivity mode, as the chip that does actually encode the video receives the same bitrate as usual, the color depth is reduced to 2 bits per channel (from 4) for a choice of 64 colors. These restrictions do not apply to AGA (A1200, A4000, CD32) Amiga, which are a different beast. To display the picture from an Amiga today, I do use and recommend the OSSC (Open Source Scan Converter) and a modern monitor with HDMI input.
- aruggirello 7y ago
  To expand on this, apps could also (ab)use "overscan" modes, which granted slightly larger resolution but image quality at the corner/borders was often somewhat unreliable.
  - snvzz 7y ago
    Image quality on overscan is alright. This is very testable by throwing the video output through the OSSC. There are restrictions on some aspects of overscan display, however. They vary between generations of Amiga chipset. e.g. It might not be possible to display sprites outside of a certain area, or display them at all if overscan is large enough.
- snvzz 7y ago
  Addendum to the first line: SuperHigh starts at ECS, so it's not available yet on OCS.

by avel 7y ago

snvzz 7y ago

>"high res" (640x512) In OCS Amiga, Low/High/SuperHigh are defined by the base (as in not using overscan) Horizontal resolution, 320/640/1280. PAL and NTSC are 256 and 200 lines base vertical resolution respectively, and 50/60Hz vertical refresh rate respectively. 512 and 400 lines are Interlaced modes. The flickering has to do with the interlacing. The improvement perceived with the NTSC mode is due to the increased vertical refresh rate. ECS Amiga (A500+/A600/A3000) introduces the so-called Productivity modes, which are just the 512/400 lines hires modes but in Progressive, thus doubling the horizontal refresh rate to ~31KHz, while also doubling the DMA bandwidth required. At full DMA you can form a a palette of 2^2 colors instead of the usual hires 2^4, and unless you have FAST RAM you'll want to keep it at 2 color in order to let the CPU use the odd ram access cycles. This palette can of course be changed during horizontal blanking, as then the display DMAs are off and the copper has room to access the palette registers, or several times midline if only using 2 colors. In Productivity mode, as the chip that does actually encode the video receives the same bitrate as usual, the color depth is reduced to 2 bits per channel (from 4) for a choice of 64 colors. These restrictions do not apply to AGA (A1200, A4000, CD32) Amiga, which are a different beast. To display the picture from an Amiga today, I do use and recommend the OSSC (Open Source Scan Converter) and a modern monitor with HDMI input.

aruggirello 7y ago
To expand on this, apps could also (ab)use "overscan" modes, which granted slightly larger resolution but image quality at the corner/borders was often somewhat unreliable.
- snvzz 7y ago
  Image quality on overscan is alright. This is very testable by throwing the video output through the OSSC. There are restrictions on some aspects of overscan display, however. They vary between generations of Amiga chipset. e.g. It might not be possible to display sprites outside of a certain area, or display them at all if overscan is large enough.
snvzz 7y ago
Addendum to the first line: SuperHigh starts at ECS, so it's not available yet on OCS.