Hello,
On Tuesday, 30 October 2018 17:48:12 EET Kieran Bingham wrote:
> On 30/10/2018 14:36, Jiri Slaby wrote:
> > Hi,
> >
> > I have a Dell Lattitude 7280 with two webcams. The standard one works
> > fine (/dev/video0). The other one is an IR camera (/dev/video1). The
> > camera proper works fine and produces 340x374 frames. But there is an IR
> > led supposed to light the object. The video is 30fps, but the LED seems
> > to emit light only on half of the frames, i.e. on every second frame (15
> > fps). This makes the video blink a lot. The two consecutive frames look
> > like:
> > https://www.fi.muni.cz/~xslaby/sklad/mpv-shot0002.jpg
> > https://www.fi.muni.cz/~xslaby/sklad/mpv-shot0003.jpg
> >
> > Do you have any ideas what to check/test?
>
> I have an HP Spectre with IR camera, and it also 'flashes' alternate frames.
>
> I assumed this was something to do with controlling the lighting for
> face recognition some how.
>
> I'm fairly sure we don't control the 'IR flash' from the UVC.
>
> I wonder if there is a control parameter for the IR led in the
> extension-units?
[snip]
> > VideoControl Interface Descriptor:
> > bLength 18
> > bDescriptorType 36
> > bDescriptorSubtype 2 (INPUT_TERMINAL)
> > bTerminalID 11
> > wTerminalType 0x0201 Camera Sensor
> > bAssocTerminal 0
> > iTerminal 0
> > wObjectiveFocalLengthMin 0
> > wObjectiveFocalLengthMax 0
> > wOcularFocalLength 0
> > bControlSize 3
> > bmControls 0x00000000
> > VideoControl Interface Descriptor:
> > bLength 11
> > bDescriptorType 36
> > bDescriptorSubtype 5 (PROCESSING_UNIT)
> > Warning: Descriptor too short
> > bUnitID 9
> > bSourceID 11
> > wMaxMultiplier 0
> > bControlSize 2
> > bmControls 0x00000000
> > iProcessing 0
> > bmVideoStandards 0x09
> > None
> > SECAM - 625/50
> > VideoControl Interface Descriptor:
> > bLength 9
> > bDescriptorType 36
> > bDescriptorSubtype 3 (OUTPUT_TERMINAL)
> > bTerminalID 8
> > wTerminalType 0x0101 USB Streaming
> > bAssocTerminal 0
> > bSourceID 10
> > iTerminal 0
> > VideoControl Interface Descriptor:
> > bLength 25
> > bDescriptorType 36
> > bDescriptorSubtype 6 (EXTENSION_UNIT)
> > bUnitID 12
> > guidExtensionCode {45b5da73-23c1-4a3d-a368-610f078c4397}
> > bNumControl 0
> > bNrPins 1
> > baSourceID( 0) 9
> > bControlSize 0
> > iExtension 0
This extension unit is strange, it exposes no control.
> > VideoControl Interface Descriptor:
> > bLength 27
> > bDescriptorType 36
> > bDescriptorSubtype 6 (EXTENSION_UNIT)
> > bUnitID 10
> > guidExtensionCode {1229a78c-47b4-4094-b0ce-db07386fb938}
> > bNumControl 2
> > bNrPins 1
> > baSourceID( 0) 12
> > bControlSize 2
> > bmControls( 0) 0x00
> > bmControls( 1) 0x06
> > iExtension 0
This one exposes two controls, which are likely used to control the IR light.
I however suspect that the controls merely expose an indirect way to read/
write internal registers, so we would really need to capture a USB trace when
using the device in Windows (assuming that the machine is shipped with
software that can control the IR light).
[snip]
--
Regards,
Laurent Pinchart
