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LF2301 Datasheet(PDF) 9 Page - LOGIC Devices Incorporated |
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LF2301 Datasheet(HTML) 9 Page - LOGIC Devices Incorporated |
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9 / 18 page  DEVICES INCORPORATED Video Imaging Products 2-9 LF2301 Image Resampling Sequencer 08/16/2000–LDS.2301-H Image Rotation & Bilinear Interpolation Figure 8 shows an example of rotating an image 30º and using bilinear interpolation. This mode is selected by loading M1-0 with “00” for a clockwise spiral walk. A counterclockwise spiral walk could be selected by loading M1-0 with “10.” Bilinear interpolation requires a kernel size of 2 x 2 pixels. Loading K3-0 with “0001” selects a kernel size of 2 x 2. The first pixel selected is determined by x0 and y0. In this example, the first pixel is (0,0). In this case, the LF2301s should address consecutive pixels during each spiral walk. For this to occur, FOV must be set to 1 (F2-0 loaded with “001”). After the last pixel of a spiral walk has been selected, the next pixel address is determined by adding dx/du to the current X address and by adding dy/du to the current Y address (unless the kernel just completed was the last for that line). At the end of the first spiral walk, pixel (0,1) is ad- dressed. Since the next calculated pixel should be (0.866,0.5), dx/du is selected to be 0.866 and dy/du is selected to be 0.5. However, after adding dx/du and dy/du to the X and Y addresses respectively, the generated address is (0.866,1.5). The Y address is off by a value of 1. This is due to the fact that the last pixel address of a spiral walk is used to calculate the first pixel address of the next spiral walk. In order for the LF2301s to generate the correct result, dy/du must be modified by subtract- ing a 1 from it. The correct value of dy/du is -0.5. Figure 6 shows how the unmodified differential terms were calculated. After the last pixel of the last spiral walk on the first line has been selected, the first pixel address of the second line is determined by adding dx/dv to x0 and by adding dy/dv to y0. Since the first calculated pixel of the first TABLE 7. PARAMETER REGISTERS ADDR Row (HEX) Column (HEX) 0000 000 000 0001 FFF FFF 0010 000 000 0011 000 100 0100 DDB 800 0101 100 1FF 0110 800 DDB 0111 1FF 100 1000 000 000 1001 000 000 1010 000 000 1011 000 000 1100 000 000 1101 000 000 1110 000 000 1111 002 002 spiral walk on the second line should be (-0.5,0.866), dx/dv is selected to be -0.5 and dy/dv is selected to be 0.866. Second order differential terms are not used in this transform and are therefore set to 0. It is important to note that the integer portion of the address generated in the LF2301 is used as the X or Y pixel address. The fractional portion (sub-pixel portion) is used as the coefficient RAM address. UMIN and VMIN are both selected to be 0. UMAX and VMAX are both selected to be 2. Table 7 shows the values loaded into all Parameter Registers. Table 8 shows the ITS outputs for this example. 30 º length =1 dx dv dx du dy du dy dv y x v u calculated pixels source image pixels FIGURE 7. 30 °°°°° IMAGE ROTATION 1,2 34 5 0123 1 2 3 4 1 = 1st pixel of 1st spiral walk, calculated pixels 0 -1 source image pixels 2 = 1st pixel of 2nd spiral walk, etc. FIGURE 8. 30 °°°°° IMAGE ROTATION FIGURE 6. DIFFERENTIAL TERMS dx du dx dv = cos 30 º dy du dy dv = = = = 0.866 sin 30 º = 0.5 –sin 30 º= –0.5 cos 30 º = 0.866 |
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