diff --git a/docs/impl/reports/USB-CAMERA.md b/docs/impl/reports/USB-CAMERA.md index 3aa9211..4a23f87 100644 --- a/docs/impl/reports/USB-CAMERA.md +++ b/docs/impl/reports/USB-CAMERA.md @@ -91,6 +91,34 @@ frames found*). UVC MJPEG commonly omits the Huffman tables, which `jpegdec` fills in and NVIDIA's decoder does not; not investigated further. The CPU figures include software JPEG decoding. +### Manual exposure and gain (1280×720, 60 fps requested, same scene) + +Both controls are honored and read back as set. Brightness is the frame mean (0–255); +noise is the standard deviation over a flat patch of ceiling. + +| Exposure | Gain | Delivered | Mean | Flat patch: mean / std | +|---|---|---|---|---| +| auto | auto | 18.7 fps | 137 | 160 / 3.9 | +| 0.1 ms | 0 | 50 fps | 3 | 2 / 0.1 | +| 0.1 ms | 240 | 50 fps | 135 | 151 / **31.3** | +| 1 ms | 240 | 50 fps | 219 | 250 (clipped) | +| 10 ms | 0 | 50 fps | 9 | 7 / 0.9 | +| 16.6 ms | 0 | 50 fps | 16 | 12 / 1.0 | +| 33.3 ms | 0 | **23 fps** | 31 | 26 / 1.9 | +| 100 ms requested | 0 | **16.5 fps** | 44 | 41 / 2.5 | + +- **Frame rate holds to ~16.6 ms of exposure**, then the frame time follows the + exposure. Auto exposure takes that trade freely, and **nothing tells it not to**: + there is no `exposure_dynamic_framerate` control. A pipeline that needs a fixed + rate has to run exposure manually and do its own metering. +- **Exposure tops out near 50–60 ms**, whatever the control's 1 s range says: + asking for 100 ms gave 1.45× the brightness of 33 ms and a 60 ms frame time. +- **Gain is very large:** 0.1 ms at full gain matches auto exposure's brightness, + roughly 1000–2000× over gain 0, and is very noisy (std 31 against 4). +- **Sensor identity stays unproven.** The gain range is consistent with a + STARVIS-class sensor; a night test against a reference camera would settle + low-light performance, and the bridge cannot. + ## What it means | Use | Fits? | @@ -106,7 +134,7 @@ The USB 2.0 hub it shares with the modem has headroom: 7.3 MB/s of MJPEG is ## Open - Daylight and night frame rates and frame sizes in the car, on a real road - scene. + scene; noise at the gain night driving needs. - Mounting and orientation (the image can be flipped in the pipeline; the camera has no flip control). - Whether the bridge's MJPEG can be made acceptable to `nvjpegdec` (inserting