Subversion Repositories video_dithering

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

entity eDither  is

   generic

   (

      img_width       : integer := 512;

      img_height      : integer := 512;

      color_width     : integer := 8;

      reduced_width   : integer := 4

   );

   port

   (

      clk       : in  std_logic;

      enable    : in  std_logic;

      x         : in  integer range 0 to img_width-1;

      din_r     : in  std_logic_vector(color_width-1 downto 0);

      din_g     : in  std_logic_vector(color_width-1 downto 0);

      din_b     : in  std_logic_vector(color_width-1 downto 0);

      dout_r    : out std_logic_vector(color_width-1 downto 0) := (others => '0');

      dout_g    : out std_logic_vector(color_width-1 downto 0) := (others => '0');

      dout_b    : out std_logic_vector(color_width-1 downto 0) := (others => '0')

   );

end entity;

architecture arch of eDither is

   constant dither_bits : integer := color_width - reduced_width;

   -- intermediate signals for caclulation

   type t_dither_rgb is array(1 to 3) of unsigned(dither_bits-1 downto 0);

   signal dither_buffer_next : t_dither_rgb := (others => (others =>'0'));

   signal dither_buffer_newline : t_dither_rgb := (others => (others =>'0'));

   signal dither_buffer_toRam : t_dither_rgb := (others => (others =>'0'));

   signal dither_buffer_fromRam : t_dither_rgb := (others => (others =>'0'));

   -- infered ram for holding old pixel information

   type t_dither_buffer is array(0 to img_width-1) of unsigned((dither_bits * 3)-1 downto 0);

   signal dither_buffer : t_dither_buffer := (others => (others => '0'));

   signal index : integer range 0 to img_width-1 := 0;

   signal AddrA : integer range 0 to img_width-1 := 0;

   signal AddrB : integer range 0 to img_width-1 := 0;

   signal WEA   : std_logic := '0';

begin

   process (clk)

      type t_intermediate is array(1 to 3) of unsigned(color_width downto 0);

      variable intermediate_color : t_intermediate;

   begin

      if rising_edge(clk) then

         -- calculate dithered colors

         if (enable = '1') then

            intermediate_color(1) := ("0" & unsigned(din_r)) + dither_buffer_next(1) + unsigned(dither_buffer_fromRam(1));

            intermediate_color(2) := ("0" & unsigned(din_g)) + dither_buffer_next(2) + unsigned(dither_buffer_fromRam(2));

            intermediate_color(3) := ("0" & unsigned(din_b)) + dither_buffer_next(3) + unsigned(dither_buffer_fromRam(3));

            for c in 1 to 3 loop

               if (intermediate_color(c)(8) = '1') then intermediate_color(c) := '0' & to_unsigned((2**color_width) - 1, color_width); end if;

               dither_buffer_next(c) <= "0" & intermediate_color(c)(dither_bits-1 downto 1);

               dither_buffer_newline(c) <= "00" & intermediate_color(c)(dither_bits-1 downto 2);

               dither_buffer_toRam(c) <= ("00" & intermediate_color(c)(dither_bits-1 downto 2)) + dither_buffer_newline(c);

            end loop;

         else

            intermediate_color(1) := "0" & unsigned(din_r);

            intermediate_color(2) := "0" & unsigned(din_g);

            intermediate_color(3) := "0" & unsigned(din_b);

         end if;

         -- calculate address for line buffer + enable

         if (x<img_width-2) then

            AddrB <= x+2;

         elsif (x=img_width-2) then

            AddrB <= 0;

         else

            AddrB <= 1;

         end if;

         index <= x;

         AddrA <= index;

         if (enable = '1') then

            WEA <= '1';

         else

            WEA <= '0';

         end if;

         -- line buffer memory

         if (WEA = '1') then

            dither_buffer(AddrA) <= dither_buffer_toRam(1) & dither_buffer_toRam(2) & dither_buffer_toRam(3);

         end if;

         dither_buffer_fromRam(1) <= dither_buffer(AddrB)((dither_bits * 3)-1 downto (dither_bits * 2));

         dither_buffer_fromRam(2) <= dither_buffer(AddrB)((dither_bits * 2)-1 downto dither_bits);

         dither_buffer_fromRam(3) <= dither_buffer(AddrB)(dither_bits-1 downto 0);

         -- map outputs

         dout_r <= std_logic_vector(intermediate_color(1)(color_width-1 downto 0));

         dout_g <= std_logic_vector(intermediate_color(2)(color_width-1 downto 0));

         dout_b <= std_logic_vector(intermediate_color(3)(color_width-1 downto 0));

      end if;

   end process;

end architecture;