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marcan42's profile
Hector Martin
Hector Martin
Hector Martin
@marcan42

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Hector Martin

@marcan42

If it ain't broke, I'll fix it! I'm porting Linux to Apple Silicon Macs at @AsahiLinux. http://patreon.com/marcan  | http://github.com/sponsors/marcan 

Tokyo, Japan
marcan.st
Joined May 2009

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    1. Hector Martin‏ @marcan42 9 Jun 2020
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      (Right click and open those images at original resolution to get the proper idea; Twitter always scales by default)

      2 replies 0 retweets 10 likes
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    2. Hector Martin‏ @marcan42 9 Jun 2020
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      I would rate the artifacts at 720p as a bit worse than the LGP2, but not terrible (chinese left, LGP2 right). This is after adjusting the brightness/contrast/saturation/hue on both to attempt to match the original image (neither has good defaults).pic.twitter.com/sVYN4OVp5t

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    3. Hector Martin‏ @marcan42 9 Jun 2020
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      So I would call this a fairly capable 720p capture card overall, and only slightly lower performance at that resolution than devices that cost 10 times as much. At 1080p things are a bit messier, but it does work.

      3 replies 0 retweets 22 likes
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    4. Iris Johnson‏ @modwizcode 9 Jun 2020
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      Replying to @marcan42

      Any idea why they seem to actively have applied filtering that makes the quality significantly worse? I could understand if it was an analogue capture since the filtering is harder to get right but this is HDMI...

      1 reply 0 retweets 0 likes
    5. Hector Martin‏ @marcan42 9 Jun 2020
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      Replying to @modwizcode

      Maybe it can't actually encode 2 megapixels worth of JPEG, and they cheat by halving the resolution and just padding the coefficients with zeroes on the right side?

      1 reply 0 retweets 1 like
    6. Iris Johnson‏ @modwizcode 9 Jun 2020
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      Replying to @marcan42

      I totally overlooked the need to do the MJPEG compression. Still, it does seem to have some sort of capture ASIC and I feel like MJPEG would be an obvious built-in feature, and 2M is not... a large image. That probably wouldn't explain the weird sharpening for 720p though.

      1 reply 0 retweets 0 likes
    7. Hector Martin‏ @marcan42 9 Jun 2020
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      Replying to @modwizcode

      The MJPEG is definitely done in hardware, but that IP block might be underpowered. Or maybe it's a bitrate thing. Or a limitation of the pixel interface or some other layer.

      2 replies 0 retweets 1 like
    8. Loïc Yhuel‏ @LYhuel 9 Jun 2020
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      Replying to @marcan42 @modwizcode

      Are the captured frames the same or similar for p30 and p60 input ? An intermediate 960x1080p60 with half the pixel clock could explain the artifacts, but then I don't know how it could transform into 1080p30 without any DRAM.

      1 reply 0 retweets 0 likes
    9. Hector Martin‏ @marcan42 9 Jun 2020
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      Replying to @LYhuel @modwizcode

      It needs RAM to stream YUV frames slower anyway... And only having 1 megapixel worth of built-in RAM would explain the limitation too.

      2 replies 0 retweets 1 like
    10. Iris Johnson‏ @modwizcode 9 Jun 2020
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      Replying to @marcan42 @LYhuel

      Yeah you beat me to it, but I think limited on-board RAM would easily explain the video resolution issues. Also makes sense since designing an ASIC would likely not want to dedicate area for anything more than the minimum. (assuming RAM is on the ASIC)

      1 reply 0 retweets 0 likes
      Hector Martin‏ @marcan42 9 Jun 2020
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      Replying to @modwizcode @LYhuel

      Yeah, there's no external memory. It's all onboard.

      10:48 PM - 9 Jun 2020
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