Auto White Balance - 2023.2 English

Grayworld whitebalancing algorithm:

This algorithm scales the values of pixels based on a gray-world assumption which states that the average of all channels should result in a gray image. It adds a modification which thresholds pixels based on their saturation value and only uses pixels below the provided threshold in finding average pixel values. Saturation is calculated using the following for a 3-channel RGB image per pixel I and is in the range [0, 1]:

A threshold of 1 means that all pixels are used to white-balance, while a threshold of 0 means no pixels are used. Lower thresholds are useful in white-balancing saturated images.

Simple whitebalancing algorithm:

A simple white balance algorithm that works by independently stretching each of the input image channels to the specified range(maximum and minimum). Computes channel wise intensity histogram and ignores p% maximum and minimum values and finally normalize each channel with min and max. For increased robustness it ignores the top and bottom \(p\%\ \ (4\%\ is\ fixed)\) of pixel values.

API Syntax for Simple white balance

template <int SRC_T, int DST_T, int ROWS, int COLS, int NPC = 1, int WB_TYPE, int HIST_SIZE, int XFCVDEPTH_IN_1 = _XFCVDEPTH_DEFAULT, int XFCVDEPTH_OUT_1 = _XFCVDEPTH_DEFAULT>
void AWBhistogram(xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_IN_1>& src1,
              xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_OUT_1>& src2,
              uint32_t histogram[3][HIST_SIZE],
              float thresh,
              float inputMin,
              float inputMax,
              float outputMin,
              float outputMax)

template <int SRC_T, int DST_T, int ROWS, int COLS, int NPC = 1, int WB_TYPE, int HIST_SIZE, int XFCVDEPTH_IN_1 = _XFCVDEPTH_DEFAULT, int XFCVDEPTH_OUT_1 = _XFCVDEPTH_DEFAULT>
void AWBNormalization(xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_IN_1>& src,
                  xf::cv::Mat<DST_T, ROWS, COLS, NPC, XFCVDEPTH_OUT_1>& dst,
                  uint32_t histogram[3][HIST_SIZE],
                  float thresh,
                  float inputMin,
                  float inputMax,
                  float outputMin,
                  float outputMax)

API Syntax for Grayworld white balance

template <int SRC_T, int DST_T, int ROWS, int COLS, int NPC = 1, int WB_TYPE, int XFCVDEPTH_IN_1 = _XFCVDEPTH_DEFAULT, int XFCVDEPTH_OUT_1 = _XFCVDEPTH_DEFAULT>
void AWBChannelGain(xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_IN_1>& src,
                xf::cv::Mat<DST_T, ROWS, COLS, NPC, XFCVDEPTH_OUT_1>& dst,
                float thresh,
                int i_gain[3])

template <int SRC_T, int DST_T, int ROWS, int COLS, int NPC = 1, int WB_TYPE, int XFCVDEPTH_IN_1 = _XFCVDEPTH_DEFAULT, int XFCVDEPTH_OUT_1 = _XFCVDEPTH_DEFAULT>
void AWBGainUpdate(xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_IN_1>& src1,
               xf::cv::Mat<DST_T, ROWS, COLS, NPC, XFCVDEPTH_OUT_1>& src2,
               float thresh,
               int i_gain[3])

Parameter Descriptions

The following table describes the template and the function parameters.

Table 291 Table Autowhitebalance Parameter Description
Parameter	Description
SRC_T	Input Pixel Type.XF_8UC3,XF_16UC3 are supported
DST_T	Output Pixel Type.XF_8UC3,XF_16UC3 are supported
ROWS	Maximum height of input and output image (Must be multiple of NPC)
COLS	Maximum width of input and output image (Must be multiple of NPC)
NPC	Number of Pixels to be processed per cycle.XF_NPPC1,XF_NPPC2,XF_NPPC4 and XF_NPPC8.
WB_TYPE	White balance type. Supported types are Gray world and simple.
HIST_SIZE	Histogram size.
USE_URAM	Enable to map storage structures to UltraRAM.
XFCVDEPTH_IN_1	Depth of input image
XFCVDEPTH_OUT_1	Depth of output image
Src1	Input image.
Src2	Input image.
histogram	Histogram array for the Simple AWB.
i_gain	Gain values for gray-world AWB.
dst	Output image.
thresh	Threshold value, which is used in gray world white balance method to compute average pixel values below the threshold value.
inputMin	Input image range minimum value.
inputMax	Input image range maximum value.
outputMin	Output image range minimum value.
outputMax	Output image range maximum value.

Resource Utilization

The following table summarizes the resource utilization of the kernel in different configurations, generated using Vitis HLS 2020.1 tool for the Xilinx xc7vx485t-ffg1157-1 FPGA, to process a 4K image.

Table 292 Table Autowhitebalance Resource Utilization Summary
Operating Mode	Operating Frequency (MHz)	Utilization Estimate
Operating Mode	Operating Frequency (MHz)	BRAM_18K	DSP_48Es	FF	LUT	CLB
1 pixel	300	14	10	4798	4953	1757
2 pixel	300	14	10	8335	8535	2901

Performance Estimate

The following table summarizes a performance estimate of the kernel in different configurations, as generated using Vitis HLS 2020.1 tool for the Xilinx xc7vx485t-ffg1157-1 FPGA, to process a 4K image.

Table 293 Table Autowhitebalance Function Performance Estimate Summary
Operating Mode	Operating Frequency (MHz)	Latency Estimate
Operating Mode	Operating Frequency (MHz)	Max (ms)
1 pixel	300	55.2 for still image(27.9 for video stream)
2 pixel	300	28 for still image(14.2 for video stream)