4 ms·

I don't know where you get "1 byte per pixel" from. At minimum, raw 4:2:0 video would be two bytes per pixel, and RGB would be three bytes per pixel with 8-bit

I don't know where you get "1 byte per pixel" from. At minimum, raw 4:2:0 video would be two bytes per pixel, and RGB would be three bytes per pixel with 8-bit color depth.

Dylan16807 4y ago
When talking about digital cameras, each "pixel" is a single color sensor. Blame marketing. Also 4:2:0 is 6 values per 4 pixels. 1.5 bytes per pixel at 8-bit.
nybble41 4y ago
You're talking about processed color frames. The GP was suggesting that the camera stream the raw sensor data, which doesn't have individual color channels, just a monochrome grid with 10 or 12 bits of usable data per pixel. A bayer filter[0] is placed in front of the sensor so that a given color of light falls on each cell. The USB host would be responsible for applying a demosaicing[0] algorithm to create the color channels from the raw sensor data. If we take the AR0330 sensor used in the USB Camera C1[2] as an example, it has a native resolution of 2304H x 1296V and outputs 10 bits per native pixel after internal A-Law compression[3] for a total raw frame size of 3.56 MiB, assuming optimal packing. The corresponding image, demosaiced and downscaled to Full HD (1920x1080), in RGB with eight bits per channel would be 5.93 MiB. [0] https://en.wikipedia.org/wiki/Bayer_filter https://en.wikipedia.org/wiki/Bayer_filter [1] https://en.wikipedia.org/wiki/Demosaicing https://en.wikipedia.org/wiki/Demosaicing [2] https://www.kurokesu.com/shop/cameras/CAMUSB1 https://www.kurokesu.com/shop/cameras/CAMUSB1 [3] https://www.onsemi.com/products/sensors/image-sensors/ar0330 https://www.onsemi.com/products/sensors/image-sensors/ar0330
- masklinn 4y ago
  > it has a native resolution of 2304H x 1296V Seems to me like that kills the idea dead? GGP assumed 8bpp and that the raw resolution matched the output, and came out... well wrong (the effective bulk transfer rate of USB 2.0 is 53MB/s on a good day), but by just a few megs. However the raw resolution is 40% higher than the final output, meaning even at 8bpp you're at 85MB/s and you've blown way past any hope of recovering via a few tricks. At 10 bpp you're above 100MB/s.
  - nybble41 4y ago
    Native resolution at 10bpp requires 40% less data per frame than the final Full HD RGB output at 8bpp per channel (24bpp total), so it would represent some savings. The problem is that neither format fits within the limits of USB 2.0 at 15 FPS or higher. To achieve a reasonable framerate you need to apply compression, and generally speaking you'll get better compression if you demosaic first.

I don't know where you get "1 byte per pixel" from. At minimum, raw 4:2:0 video would be two bytes per pixel, and RGB would be three bytes per pixel with 8-bit color depth.

Dylan16807 4y ago

When talking about digital cameras, each "pixel" is a single color sensor. Blame marketing. Also 4:2:0 is 6 values per 4 pixels. 1.5 bytes per pixel at 8-bit.

nybble41 4y ago

You're talking about processed color frames. The GP was suggesting that the camera stream the raw sensor data, which doesn't have individual color channels, just a monochrome grid with 10 or 12 bits of usable data per pixel. A bayer filter[0] is placed in front of the sensor so that a given color of light falls on each cell. The USB host would be responsible for applying a demosaicing[0] algorithm to create the color channels from the raw sensor data. If we take the AR0330 sensor used in the USB Camera C1[2] as an example, it has a native resolution of 2304H x 1296V and outputs 10 bits per native pixel after internal A-Law compression[3] for a total raw frame size of 3.56 MiB, assuming optimal packing. The corresponding image, demosaiced and downscaled to Full HD (1920x1080), in RGB with eight bits per channel would be 5.93 MiB. [0] https://en.wikipedia.org/wiki/Bayer_filter https://en.wikipedia.org/wiki/Bayer_filter [1] https://en.wikipedia.org/wiki/Demosaicing https://en.wikipedia.org/wiki/Demosaicing [2] https://www.kurokesu.com/shop/cameras/CAMUSB1 https://www.kurokesu.com/shop/cameras/CAMUSB1 [3] https://www.onsemi.com/products/sensors/image-sensors/ar0330 https://www.onsemi.com/products/sensors/image-sensors/ar0330

masklinn 4y ago
> it has a native resolution of 2304H x 1296V Seems to me like that kills the idea dead? GGP assumed 8bpp and that the raw resolution matched the output, and came out... well wrong (the effective bulk transfer rate of USB 2.0 is 53MB/s on a good day), but by just a few megs. However the raw resolution is 40% higher than the final output, meaning even at 8bpp you're at 85MB/s and you've blown way past any hope of recovering via a few tricks. At 10 bpp you're above 100MB/s.
- nybble41 4y ago
  Native resolution at 10bpp requires 40% less data per frame than the final Full HD RGB output at 8bpp per channel (24bpp total), so it would represent some savings. The problem is that neither format fits within the limits of USB 2.0 at 15 FPS or higher. To achieve a reasonable framerate you need to apply compression, and generally speaking you'll get better compression if you demosaic first.