7. BCM2835 ISP Driver¶

7.1. Introduction¶

The BCM2835 Image Sensor Pipeline (ISP) is a fixed function hardware pipeline for performing image processing operations. Images are fed to the input of the ISP through memory frame buffers. These images may be in various YUV, RGB, or Bayer formats. A typical use case would have Bayer images obtained from an image sensor by the BCM2835 Unicam peripheral, written to a memory frame buffer, and finally fed into the input of the ISP. Two concurrent output images may be generated in YUV or RGB format at different resolutions. Statistics output is also generated for Bayer input images.

The bcm2835-isp driver exposes the following media pads as V4L2 device nodes:

Pad	Direction	Purpose	Formats
“bcm2835-isp0-output0”	sink	Accepts Bayer, RGB or YUV format frame buffers as input to the ISP HW pipeline.	RAW8, RAW10P, RAW12P, RAW14P, RAW16, RGB24/BGR24, YUYV, YVYU, UYVY, VYUY, YUV420/YVU420
“bcm2835-isp0-capture1”	source	High resolution YUV or RGB processed output from the ISP.	RGB565, RGB24/BGR24, ABGR32, YUYV, YVYU, UYVY, VYUY. YUV420/YVU420, NV12/NV21,
“bcm2835-isp0-capture2”	source	Low resolution YUV processed output from the ISP. The output of this pad cannot have a resolution larger than the “bcm2835-isp0-capture1” pad in any dimension.	YUYV, YVYU, UYVY, VYUY. YUV420/YVU420, NV12/NV21,
“bcm2835-isp0-capture1”	source	Image statistics calculated from the input image provided on the “bcm2835-isp0-output0” pad. Statistics are only available for Bayer format input images.	V4L2_META_FMT_BCM2835_ISP_STATS (‘BSTA’).

7.2. Pipeline Configuration¶

The ISP pipeline can be configure through user-space by calling VIDIOC_S_EXT_CTRLS on the “bcm2835-isp0-output0” node with the appropriate parameters as shown in the table below.

id	Parameter
`V4L2_CID_USER_BCM2835_ISP_CC_MATRIX`	struct `bcm2835_isp_custom_ccm`
`V4L2_CID_USER_BCM2835_ISP_LENS_SHADING`	struct `bcm2835_isp_lens_shading`
`V4L2_CID_USER_BCM2835_ISP_BLACK_LEVEL`	struct `bcm2835_isp_black_level`
`V4L2_CID_USER_BCM2835_ISP_GEQ`	struct `bcm2835_isp_geq`
`V4L2_CID_USER_BCM2835_ISP_GAMMA`	struct `bcm2835_isp_gamma`
`V4L2_CID_USER_BCM2835_ISP_DENOISE`	struct `bcm2835_isp_denoise`
`V4L2_CID_USER_BCM2835_ISP_SHARPEN`	struct `bcm2835_isp_sharpen`
`V4L2_CID_USER_BCM2835_ISP_DPC`	struct `bcm2835_isp_dpc`

7.2.1. Configuration Parameters¶

struct bcm2835_isp_rational¶: Rational value type.

Definition

struct bcm2835_isp_rational {
  __s32 num;
  __u32 den;
};

Members

num: Numerator.
den: Denominator.

struct bcm2835_isp_ccm¶: Colour correction matrix.

Definition

struct bcm2835_isp_ccm {
  struct bcm2835_isp_rational ccm[3][3];
  __s32 offsets[3];
};

Members

ccm: 3x3 correction matrix coefficients.
offsets: 1x3 correction offsets.

struct bcm2835_isp_custom_ccm¶: Custom CCM applied with the V4L2_CID_USER_BCM2835_ISP_CC_MATRIX ctrl.

Definition

struct bcm2835_isp_custom_ccm {
  __u32 enabled;
  struct bcm2835_isp_ccm ccm;
};

Members

enabled: Enable custom CCM.
ccm: Custom CCM coefficients and offsets.

enum bcm2835_isp_gain_format¶: format of the gains in the lens shading tables used with the V4L2_CID_USER_BCM2835_ISP_LENS_SHADING ctrl.

Constants

GAIN_FORMAT_U0P8_1: Gains are u0.8 format, starting at 1.0
GAIN_FORMAT_U1P7_0: Gains are u1.7 format, starting at 0.0
GAIN_FORMAT_U1P7_1: Gains are u1.7 format, starting at 1.0
GAIN_FORMAT_U2P6_0: Gains are u2.6 format, starting at 0.0
GAIN_FORMAT_U2P6_1: Gains are u2.6 format, starting at 1.0
GAIN_FORMAT_U3P5_0: Gains are u3.5 format, starting at 0.0
GAIN_FORMAT_U3P5_1: Gains are u3.5 format, starting at 1.0
GAIN_FORMAT_U4P10: Gains are u4.10 format, starting at 0.0

struct bcm2835_isp_lens_shading¶: Lens shading tables supplied with the V4L2_CID_USER_BCM2835_ISP_LENS_SHADING ctrl.

Definition

struct bcm2835_isp_lens_shading {
  __u32 enabled;
  __u32 grid_cell_size;
  __u32 grid_width;
  __u32 grid_stride;
  __u32 grid_height;
  __s32 dmabuf;
  __u32 ref_transform;
  __u32 corner_sampled;
  __u32 gain_format;
};

Members

enabled: Enable lens shading.
grid_cell_size: Size of grid cells in samples (16, 32, 64, 128 or 256).
grid_width: Width of lens shading tables in grid cells.
grid_stride: Row to row distance (in grid cells) between grid cells in the same horizontal location.
grid_height: Height of lens shading tables in grid cells.
dmabuf: dmabuf file handle containing the table.
ref_transform: Reference transform - unsupported, please pass zero.
corner_sampled: Whether the gains are sampled at the corner points of the grid cells or in the cell centres.
gain_format: Format of the gains (see enum bcm2835_isp_gain_format).

struct bcm2835_isp_black_level¶: Sensor black level set with the V4L2_CID_USER_BCM2835_ISP_BLACK_LEVEL ctrl.

Definition

struct bcm2835_isp_black_level {
  __u32 enabled;
  __u16 black_level_r;
  __u16 black_level_g;
  __u16 black_level_b;
  __u8 padding[2];
};

Members

enabled: Enable black level.
black_level_r: Black level for red channel.
black_level_g: Black level for green channels.
black_level_b: Black level for blue channel.

struct bcm2835_isp_geq¶: Green equalisation parameters set with the V4L2_CID_USER_BCM2835_ISP_GEQ ctrl.

Definition

struct bcm2835_isp_geq {
  __u32 enabled;
  __u32 offset;
  struct bcm2835_isp_rational slope;
};

Members

enabled: Enable green equalisation.
offset: Fixed offset of the green equalisation threshold.
slope: Slope of the green equalisation threshold.

struct bcm2835_isp_gamma¶: Gamma parameters set with the V4L2_CID_USER_BCM2835_ISP_GAMMA ctrl.

Definition

struct bcm2835_isp_gamma {
  __u32 enabled;
  __u16 x[BCM2835_NUM_GAMMA_PTS];
  __u16 y[BCM2835_NUM_GAMMA_PTS];
};

Members

enabled: Enable gamma adjustment.

struct bcm2835_isp_denoise¶: Denoise parameters set with the V4L2_CID_USER_BCM2835_ISP_DENOISE ctrl.

Definition

struct bcm2835_isp_denoise {
  __u32 enabled;
  __u32 constant;
  struct bcm2835_isp_rational slope;
  struct bcm2835_isp_rational strength;
};

Members

enabled: Enable denoise.
constant: Fixed offset of the noise threshold.
slope: Slope of the noise threshold.
strength: Denoise strength between 0.0 (off) and 1.0 (maximum).

struct bcm2835_isp_sharpen¶: Sharpen parameters set with the V4L2_CID_USER_BCM2835_ISP_SHARPEN ctrl.

Definition

struct bcm2835_isp_sharpen {
  __u32 enabled;
  struct bcm2835_isp_rational threshold;
  struct bcm2835_isp_rational strength;
  struct bcm2835_isp_rational limit;
};

Members

enabled: Enable sharpening.
threshold: Threshold at which to start sharpening pixels.
strength: Strength with which pixel sharpening increases.
limit: Limit to the amount of sharpening applied.

enum bcm2835_isp_dpc_mode¶: defective pixel correction (DPC) strength.

Constants

DPC_MODE_OFF: No DPC.
DPC_MODE_NORMAL: Normal DPC.
DPC_MODE_STRONG: Strong DPC.

struct bcm2835_isp_dpc¶: Defective pixel correction (DPC) parameters set with the V4L2_CID_USER_BCM2835_ISP_DPC ctrl.

Definition

struct bcm2835_isp_dpc {
  __u32 enabled;
  __u32 strength;
};

Members

enabled: Enable DPC.
strength: DPC strength (see enum bcm2835_isp_dpc_mode).