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video-controls.md

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Video controls

Enabling extended set of video control

!!! After applying all changes we must compile new kernel. Kernel building

By default is enabled only brightness video control.

For enabling more video controls is a need to change some values in kernel driver source for UVC gadget function.

These settings are located in file drivers/usb/gadget/function/f_uvc.c

And a value of bmControls field must be changed.

Default values

	cd = &opts->uvc_camera_terminal;
	cd->bLength                     = UVC_DT_CAMERA_TERMINAL_SIZE(3);
	cd->bDescriptorType             = USB_DT_CS_INTERFACE;
	cd->bDescriptorSubType          = UVC_VC_INPUT_TERMINAL;
	cd->bTerminalID                 = 1;
	cd->wTerminalType               = cpu_to_le16(0x0201);
	cd->bAssocTerminal              = 0;
	cd->iTerminal                   = 0;
	cd->wObjectiveFocalLengthMin    = cpu_to_le16(0);
	cd->wObjectiveFocalLengthMax    = cpu_to_le16(0);
	cd->wOcularFocalLength          = cpu_to_le16(0);
	cd->bControlSize                = 3;
	cd->bmControls[0]               = 2;
	cd->bmControls[1]               = 0;
	cd->bmControls[2]               = 0;

	pd = &opts->uvc_processing;
	pd->bLength                     = UVC_DT_PROCESSING_UNIT_SIZE(2);
	pd->bDescriptorType             = USB_DT_CS_INTERFACE;
	pd->bDescriptorSubType          = UVC_VC_PROCESSING_UNIT;
	pd->bUnitID                     = 2;
	pd->bSourceID                   = 1;
	pd->wMaxMultiplier              = cpu_to_le16(16*1024);
	pd->bControlSize                = 2;
	pd->bmControls[0]               = 1;
	pd->bmControls[1]               = 0;
	pd->iProcessing                 = 0;

Available settings for UVC_VC_INPUT_TERMINAL

source: USB Device Class Definition for Video Devices, Revision 1.1

Field bmControls is a bitmap type. A bit set to 1 indicates that the mentioned Control is supported for the video stream.

bit control
D0 Scanning Mode
D1 Auto-Exposure Mode
D2 Auto-Exposure Priority
D3 Exposure Time (Absolute)
D4 Exposure Time (Relative)
D5 Focus (Absolute)
D6 Focus (Relative)
D7 Iris (Absolute)
D8 Iris (Relative)
D9 Zoom (Absolute)
D10 Zoom (Relative)
D11 PanTilt (Absolute)
D12 PanTilt (Relative)
D13 Roll (Absolute)
D14 Roll (Relative)
D15 Reserved
D16 Reserved
D17 Focus, Auto
D18 Privacy
D19..(n*8-1) Reserved, set to zero

Available settings for UVC_VC_PROCESSING_UNIT

source: USB Device Class Definition for Video Devices, Revision 1.1

Field bmControls is a bitmap type.

A bit set to 1 indicates that the mentioned Control is supported for the video stream.

bit control
D0 Brightness
D1 Contrast
D2 Hue
D3 Saturation
D4 Sharpness
D5 Gamma
D6 White Balance Temperature
D7 White Balance Component
D8 Backlight Compensation
D9 Gain
D10 Power Line Frequency
D11 Hue, Auto
D12 White Balance Temperature, Auto
D13 White Balance Component, Auto
D14 Digital Multiplier
D15 Digital Multiplier Limit
D16 Analog Video Standard
D17 Analog Video Lock Status
D18..(n*8-1) Reserved. Set to zero.

Enabling more video controls

We should only turn on controls for which we have mapping between UVC and V4L2.

bit bit value control
D0 1 Brightness
D1 1 Contrast
D2 1 Hue
D3 1 Saturation
D4 1 Sharpness
D5 1 Gamma
D6 1 White Balance Temperature
D7 1 White Balance Component
pd->bmControls[0] = 255
bit bit value control
D8 0 Backlight Compensation
D9 1 Gain
D10 1 Power Line Frequency
D11 0 Hue, Auto
D12 0 White Balance Temperature, Auto
D13 0 White Balance Component, Auto
D14 0 Digital Multiplier
D15 0 Digital Multiplier Limit
pd->bmControls[1] = 6 
	pd = &opts->uvc_processing;
	pd->bLength                     = UVC_DT_PROCESSING_UNIT_SIZE(2);
	pd->bDescriptorType             = USB_DT_CS_INTERFACE;
	pd->bDescriptorSubType          = UVC_VC_PROCESSING_UNIT;
	pd->bUnitID                     = 2;
	pd->bSourceID                   = 1;
	pd->wMaxMultiplier              = cpu_to_le16(16*1024);
	pd->bControlSize                = 2;
	pd->bmControls[0]               = 255; // changed
	pd->bmControls[1]               = 6; // changed
	pd->iProcessing                 = 0;

Linux video controls mapping

Mapping between UVC and V4L2 controls

UVC control V4L2 control
UVC_PU_BRIGHTNESS_CONTROL V4L2_CID_BRIGHTNESS
UVC_PU_CONTRAST_CONTROL V4L2_CID_CONTRAST
UVC_PU_GAIN_CONTROL V4L2_CID_GAIN
UVC_PU_POWER_LINE_FREQUENCY_CONTROL V4L2_CID_POWER_LINE_FREQUENCY
UVC_PU_HUE_CONTROL V4L2_CID_HUE
UVC_PU_SATURATION_CONTROL V4L2_CID_SATURATION
UVC_PU_SHARPNESS_CONTROL V4L2_CID_SHARPNESS
UVC_PU_GAMMA_CONTROL V4L2_CID_GAMMA
UVC_PU_WHITE_BALANCE_TEMPERATURE_CONTROL V4L2_CID_WHITE_BALANCE_TEMPERATURE
UVC_PU_WHITE_BALANCE_COMPONENT_CONTROL V4L2_CID_RED_BALANCE + V4L2_CID_BLUE_BALANCE
UVC_PU_WHITE_BALANCE_COMPONENT_AUTO_CONTROL V4L2_CID_AUTO_WHITE_BALANCE
UVC_PU_HUE_AUTO_CONTROL V4L2_CID_HUE_AUTO
UVC_CT_AE_MODE_CONTROL V4L2_CID_EXPOSURE_AUTO
UVC_CT_AE_PRIORITY_CONTROL V4L2_CID_EXPOSURE_AUTO_PRIORITY