Design Description Document - 1D FIR Filter

Transcription

1 Description Design Description Document - 1D FIR Filter This design performs a 19 tap, symmetrical 1-D convolution on an image using the PIPEFlow data. This can be used as the basis for a 2-D separable filter by passing the image through the filter rowwise, and then column-wise. This can be used for effects such as: Blurring Anti-aliasing Function More specifically for a given pixel p`(x,y) the operation (for the row-wise operation) is given by:: 9 p ( x, y) = ( p( x i, y) p( x i, y)) k( i) p( x, y) * k( 0) i= 1 The coefficient values, k, are unsigned 8 bit binary numbers. Pixels outside of the image bounds are assumed to be the same as the pixel on the edge. For example x(-2,10)=x(-1,10)=x(0,10). Registers The following registers are used by the design: Coefficient k(0) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(1) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(2) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(3) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(4) 7..0 Coefficient value 8 = 1/2 R/W

2 Coefficient k(5) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(6) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(7) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(8) 7..0 Coefficient value 8 = 1/2 R/W Coefficient k(9) 7..0 Coefficient value 8 = 1/2 R/W Design Figure 1 shows the hierarchical design for the transform design. PE_1D_FIR The PE_1D_FIR is the overall design. The tasks carried out by the PE_1D_FIR block are: Connection of all the other blocks, and external signals. Working out the phase of the current data (i.e. whether it is R,G or B,α). PE_1D_FIR_REGS PE_2D_FIR_REGS implements the register file for the design. The register file stores the coefficients for the filter. PE_1D_FIR_CALC This block takes the input data and applies the filter using the method pictured in Figure 2. This block can be thought of as operating in a time multiplexed fashion, performing a complete operation every 4 clock cycles. R,G,B, & A are processed in cycles 1,2,3, & 4 respectively. This reuse of hardware means that a large filter design can be implemented on the device than would be the case if all the components were processed in parallel.

3 PIPEFlow Bus PE_1D_FIR_REGS REGS Coefficents PE_1D_FIR PIPEFlow Data PE_1D_FIR_CALC CALC PIPEFlow Data Figure 1 - Design Hierarchy R,G,B,A K(0) K(1) K(7) K(8) K(9) 4 Stages of Registers Figure 2 - Method of convolution Example Usage - Blurring In this example we will use the 1-D Filter in a two pass operation to blur the image. Original Image Figure 3 - Blurring an image Blurred Image

4 In order to use the 1-D filter to as a 2-D filter, it is necessary to perform a two pass operation. This done by passing the data through using horizontal raster scan, and then using a vertical raster scan as shown in Figure horizontal raster scan Figure 4 - Horizontal and Vertical raster scans vertical raster scan The convolution kernel used to achieve the blur is: ( ) The code below implements this example, using the SONIC API. UINT PipeNum; //Will hold the PIPE number DWORD Data; //Used to hold the data sent to the board Sonic_Initialise(); //Initialise everything for the board //Configure a spare PIPE Sonic_Conf(&PipeNum, PE_1D_FIR.RBF, PR.RBF ); Sonic_Lock_PIPE(PipeNum); //Lock the PIPE so it is not reconfigured //Write the image size into the registers in the PR Sonic_PR_ImageSize_Write(PIPENum, &ImageWidth, &ImageHeight //Write the coefficients in the PE register file Data =0x13h; //=(1/19) for (register=0; register<10 ; register) { Sonic_PE_Write(PIPENum, register, &Data); } //Setup up the PR to read the image 2 columns at a time horizontally (strip=1) //And force it to read the image form the lower part of the SRAM (000 7fffh) //Two columns are read at a time in order that there are four clock cycles between //Pixels. BOOL WriteCol=FALSE; BOOL ReadCol=FALSE; BOOL WriteUpper=FALSE; BOOL ReadUpper=FALSE; int Strip=2; Sonic_PR_ImageMode_Write(PIPENum, &Strip, &ReadCol, &ReadUpper, &WriteCol, &WriteUpper); Data=1; Sonic_PR_Pipeflow_Write(PIPENum, &Data); //Set the PR generating the PIPEFlow data do { //Set the PR generating the PIPEFlow data Sonic_PR_Pipeflow_Read(PIPENum, &Data); } while ((Data & 0x2)==0); //Wait for data to be returned //Setup up the PR to read the image 2 rows at a time vertically (strip=1) //And force it to read the image form the lower part of the SRAM (000 7fffh) //Two columns are read at a time in order that there are four clock cycles between

5 //Pixels. BOOL WriteCol=TRUE; BOOL ReadCol=TRUE; BOOL WriteUpper=FALSE; BOOL ReadUpper=FALSE; int Strip=2; Sonic_PR_ImageMode_Write(PIPENum, &Strip, &ReadCol, &ReadUpper, &WriteCol, &WriteUpper); //Retrieve the image from the lower part of the SRAM Sonic_PM_Read(PipeNum, &DstImage, ImageSize, 0x0); Sonic_Unlock_PIPE(PipeNum); //Release the PIPE Sonic_Close(); Simon Haynes 1D FIR.doc 4/5/99