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Digital Image Processing & Image Filtering

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  1. Digital Image Processing &Image Filtering Jonathan Mason Software Engineer, Harris Corp. July 10, 2003

  2. Uses of image filtering • Noise Reduction • Low Pass Filter • Image Recovery • Wiener Filter • Edge Detection • High Pass Filter

  3. The Filtering Operation • Convolution • Continuous (Analog) f * g =∫ f(τ) g(t - τ) dτ • Discrete (Digital) f(i) * g(i) = Σf(j) g(i-j)

  4. Sliding Window Approach

  5. Design Considerations • Filter Creation • Choosing Coefficients • Border Considerations • Wrap-around • Extend border • Ignore border

  6. Types of Filters • Low Pass or Averaging Filter [ 0 1 0 ] [ 1 4 1 ] [ 0 1 0 ]

  7. Types of Filters • High Pass • Horizontal Edge Detection (Sobel) [ 1 2 1 ] [ 0 0 0 ] [ -1 –2 –1 ] • Vertical Edge Detection (Sobel) [ 1 0 -1 ] [ 2 0 -2 ] [ 1 0 -1 ]

  8. High Level Design

  9. State Progression

  10. State Progression VHDL INIT: process(clock, resetn) begin led <= resetn; if (clock'event and clock = '1') then currentState <= nextState; end if; end process; STATE_PROGRESSION: process(btn, db, adr, resetn) begin if (adr = "010" and oe = '1' and cs = '1') then case thedb is when "10000000" => -- SW8 on the DIO2 board nextState <= displayImageState; when "01000000" => -- SW7 on the DIO2 board nextState <= displayInvertedImageState; when "00100000" => -- SW6 on the DIO2 board nextState <= displayLowPassFilteredImageState; when "00010000" => -- SW5 on the DIO2 board nextState <= displayHighPassHorizontalFilteredState; when "00001000" => -- SW4 on the DIO2 board nextState <= displayHighPassVerticalFilteredState; when others => nextState <= resetState; end case; end if; end process;

  11. VGA Signal

  12. Filter and Image VHDL IMAGE: process(enable, hcnt, vcnt, currentState, resetn) begin -- This is a low pass or averaging filter lpFilter <= ( 0 => (0,1,0), 1 => (1,4,1), 2 => (0,1,0) ); -- This is the vertical edge detecting high pass filter. -- Also known as a Sobel edge detector. hpvFilter <= ( 0 => (1,0,-1), 1 => (2,0,-2), 2 => (1,0,-1) ); -- This is the horizontal edge detecting high pass filter. -- Also known as a Sobel edge detector. hphFilter <= ( 0 => (1,2,1), 1 => (0,0,0), 2 => (-1,-2,-1) ); -- This is the 64x64 array of pixel values. imageValues <= ( 0 => ("100","100","100","101","101","101","101", - - -,"111"), 1 => ("101","101","100","101","101","101","101", - - -,"111"), 2 => ("101","100","100","101","100","101","101", - - -,"111"), … 63 => ("100","100","100","101","100","100","101", - - -,"111"));

  13. Image Generation VHDL IMAGE: process(enable, hcnt, vcnt, currentState, resetn) begin if (enable = '1') then if (hcnt > (H_PIXELS/2 - IMAGE_WIDTH/2) and hcnt < (H_PIXELS/2 + IMAGE_WIDTH/2)) then if (vcnt > (V_LINES/2 - IMAGE_WIDTH/2) and vcnt < (V_LINES/2 + IMAGE_WIDTH/2)) then hIndex <= conv_std_logic_vector(conv_integer(hcnt) - (H_PIXELS/2 - IMAGE_WIDTH/2),8); vIndex <= conv_std_logic_vector(conv_integer(vcnt) - (V_LINES/2 - IMAGE_WIDTH/2),8); -- If we are within the boundaries of the image, we must determine how to -- display the image, based on the current state. case currentState is when displayImageState => pixel <= imageValues(conv_integer(vIndex))(conv_integer(hIndex))(0) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(1) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(0) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(1) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(2) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(0) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(1) & imageValues(conv_integer(vIndex))(conv_integer(hIndex))(2); when others => pixel <= "00000000"; --invalid state, output no image. end case; else ---out of range of the image height, output a white background. pixel <= "11111111"; end if; else ---out of range of the image width, output a white background. pixel <= "11111111"; end if; else -- The reset button has been pressed, so output nothing. pixel <= "00000000"; end if; end process;

  14. Convolution VHDL when displayLowPassFilteredImageState => -- Display the image with the low pass filter applied. if(conv_integer(vIndex) > 0 and conv_integer(vIndex) < (IMAGE_WIDTH - 1) and conv_integer(hIndex) > 0 and conv_integer(hIndex) < (IMAGE_WIDTH - 1)) then --convolution of pixel value with the filter pixel <= conv_std_logic_vector( ( conv_integer(imageValues(conv_integer(vIndex-1))(conv_integer(hIndex-1))) * lpFilter(0)(0) + conv_integer(imageValues(conv_integer(vIndex-1))(conv_integer(hIndex))) * lpFilter(0)(1) + conv_integer(imageValues(conv_integer(vIndex-1))(conv_integer(hIndex+1))) * lpFilter(0)(2) + conv_integer(imageValues(conv_integer(vIndex)) (conv_integer(hIndex-1))) * lpFilter(1)(0) + conv_integer(imageValues(conv_integer(vIndex)) (conv_integer(hIndex))) * lpFilter(1)(1) + conv_integer(imageValues(conv_integer(vIndex)) (conv_integer(hIndex+1))) * lpFilter(1)(2) + conv_integer(imageValues(conv_integer(vIndex+1))(conv_integer(hIndex-1))) * lpFilter(2)(0) + conv_integer(imageValues(conv_integer(vIndex+1))(conv_integer(hIndex))) * lpFilter(2)(1) + conv_integer(imageValues(conv_integer(vIndex+1))(conv_integer(hIndex+1))) * lpFilter(2)(2) )/8, 3)(0) & - - - repeated for each pixel output value

  15. VGA Timing Diagram

  16. VGA Signal VHDL VERTICAL_COUNTER: process(hsyncint, resetn) begin if (resetn = '1') then vcnt <= (others => '0'); elsif (hsyncint'event and hsyncint = '1') then if vcnt < V_PERIOD then vcnt <= vcnt + 1; else vcnt <= (others => '0'); end if; end if; end process; VERTICAL_SYNC: process(hsyncint, resetn) begin if (resetn = '1') then vsync <= '1'; elsif (hsyncint'event and hsyncint = '1') then if (vcnt >= V_SYNCSTART and vcnt < V_SYNCEND) then vsync <= '0'; else vsync <= '1'; end if; end if; end process;

  17. VGA Signal Enable VHDL OUTPUT_ENABLE: process(clock) begin if (clock'event and clock = '1') then if (hcnt >= H_PIXELS or vcnt >= V_LINES) then enable <= '0'; else enable <= '1'; end if; end if; end process; end behavioral;

  18. Matlab Verification Code %read in the image fid=fopen(IMAGE_NAME); imageMatrix=fread(fid,[IMAGE_WIDTH,IMAGE_HEIGHT]); fclose(fid); %invert the matrix so that it will be displayed properly imageMatrix=imageMatrix'; %%Apply an impulse to the filter. Then calculate %%the phase and amplitude of the filter in the %%frequency domain. filtered_image = conv2(low_pass_filter,imageMatrix,'same'); v_e_d_image = conv2(vertical_edge_detector,imageMatrix,'same'); h_e_d_image = conv2(horizontal_edge_detector, imageMatrix,'same');

  19. Matlab Verification Output

  20. Project Output

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