Warp Transform - 2023.2 English

The warpTransform function is designed to perform the perspective and affine geometric transformations on an image. The type of transform is a compile time parameter to the function.

The function uses a streaming interface to perform the transformation. Due to this and due to the fact that geometric transformations need access to many different rows of input data to compute one output row, the function stores some rows of the input data in block RAMs/UltraRAMs. The number of rows the function stores can be configured by the user by modifying a template parameter. Based on the transformation matrix, you can decide on the number of rows to be stored. You can also choose when to start transforming the input image in terms of the number of rows of stored image.

Affine Transformation

The transformation matrix consists of size parameters, and is as shown:

Affine transformation is applied in the warpTransform function following the equation:

Perspective Transformation

The transformation matrix is a 3x3 matrix as shown below:

Perspective transformation is applied in warpTransform following the equation:

The destination pixel is then computed by dividing the first two dimensions of the dst1 by the third dimension

API Syntax

template<int STORE_LINES, int START_ROW, int TRANSFORMATION_TYPE, int INTERPOLATION_TYPE, int SRC_T, int ROWS, int COLS, int NPC=1, bool USE_URAM=false, int XFCVDEPTH_IN = _XFCVDEPTH_DEFAULT, int XFCVDEPTH_OUT = _XFCVDEPTH_DEFAULT>
void warpTransform(xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_IN> & src, xf::cv::Mat<SRC_T, ROWS, COLS, NPC, XFCVDEPTH_OUT> & dst, float *transformation_matrix)

Parameter Descriptions

The following table describes the template and the function parameters.

Table 755 Table . warpTransform Parameter Description
Parameter	Description
STORE_LINES	Number of lines to store an input to process a given transformation.
START_ROW	Number of the input rows to store before starting the image transformation. This must be less than or equal to STORE_LINES.
TRANSFORMATI ON_TYPE	Affine and perspective transformations are supported. Set this flag to ‘0’ for affine and ‘1’ for perspective transformation.
INTERPOLATIO N_TYPE	Set flag to ‘1’ for bilinear interpolation and ‘0’ for nearest neighbor interpolation.
SRC_T	Input and Output pixel type. Only 8-bit, unsigned, 1 and 3 channels are supported (XF_8UC1 and XF_8UC3)
ROWS	Maximum height of input and output image.
COLS	Maximum width of input and output image.
NPC	Number of pixels to be processed per cycle; only one-pixel operation supported (XF_NPPC1).
USE_URAM	Enable to map some storage structures to UltraRAM
XFCVDEPTH_IN	Depth of the input image.
XFCVDEPTH_OUT	Depth of the output image.
src	Input image
dst	Output image
transformati on_matrix	Transformation matrix that is applied to the input image.

Resource Utilization

The following table summarizes the resource utilization of the Warp transform, generated using Vivado HLS 2019.1 version tool for the Xilinx Xczu9eg-ffvb1156-1-i-es1 FPGA, to process a grayscale HD (1080x1920) image.

Table 756 Table . warpTransform Function Resource Utilization Summary
Transformation	INTERPOLATION _TYPE	STORE _LINES	START _ROW	Operating Frequency (MHz)	Utilization Estimate
Transformation	INTERPOLATION _TYPE	STORE _LINES	START _ROW	Operating Frequency (MHz)	LUTs	FFs	DSPs	BRAMs
Perspective	Bilinear	100	50	300	7468	9804	61	112
Perspective	Nearest Neighbor	100	50	300	4514	6761	35	104
Affine	Bilinear	100	50	300	6139	5606	40	124
Affine	Nearest Neighbor	100	50	300	4611	4589	18	112

The following table summarizes the resource utilization of the Warp transform, generated using Vivado HLS 2019.1 version tool for the Xilinx Xczu9eg-ffvb1156-1-i-es1 FPGA, to process a BGR 4K image.

Table 757 Table . warpTransform Function Resource Utilization Summary
Transformation	INTERPOLATION _TYPE	STORE _LINES	START _ROW	Operating Frequency (MHz)	Utilization Estimate
Transformation	INTERPOLATION _TYPE	STORE _LINES	START _ROW	Operating Frequency (MHz)	LUTs	FFs	DSPs	BRAMs
Perspective	Bilinear	100	50	300	9192	7910	48	616
Perspective	Nearest Neighbor	100	50	300	10533	12055	69	604
Affine	Bilinear	100	50	300	6397	8415	35	604

The following table summarizes the resource utilization of the Warp transform, generated using Vivado HLS 2019.1 version tool for the Xilinx xczu7ev-ffvc1156-2-e FPGA, to progress a grayscale 4K image with UltraRAM enabled.

Table 758 Table . warpTransform Function Resource Utilization Summary with UltraRAM Enable
Transformation	INTERPOLATION _TYPE	STORE _LINES	START _ROW	Operating Frequency (MHz)	Utilization Estimate
Transformation	INTERPOLATION _TYPE	STORE _LINES	START _ROW	Operating Frequency (MHz)	LUTs	FFs	DSPs	BRAMs	URAM
Perspective	Bilinear	100	50	300	7820	12458	61	7	12
Perspective	Nearest Neighbor	100	50	300	4880	8323	35	2	6
Affine	Bilinear	100	50	300	6850	9516	40	13	12
Affine	Nearest Neighbor	100	50	300	4651	6548	18	6	6

Performance Estimate

The following table summarizes a performance estimate of the Warp transform, as generated using Vivado HLS 2019.1 tool for Xilinx Xczu9eg-ffvb1156-1-i-es1 FPGA, to process a grayscale HD (1080x1920) image.

Table 759 Table . warpTransform Function Performance Estimate Summary
Transforma tion	INTERPOLATI ON _TYPE	STORE _LIN ES	START _ROW	Operatin g Frequenc y (MHz)	Latency Estimate Max (ms)
Perspectiv e	Bilinear	100	50	300	7.46
Perspectiv e	Nearest Neighbor	100	50	300	7.31
Affine	Bilinear	100	50	300	7.31
Affine	Nearest Neighbor	100	50	300	7.24