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@soldierboy

Claudeに簡単な画像処理について質問

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Last updated at Posted at 2026-07-05

Claudeに簡単な画像処理をきいてみた

画像処理の話をするとBayer，RGB，YUVといった話がよく出る．
これらについて一般的なJPEGになるまでの処理をClaudeに聞いてコードを生成した．

#include <stdint.h>

#define WIDTH  1920
#define HEIGHT 1080

static uint8_t clamp_u8( int val )
{
  if( val<0 ) {
    return 0;
  } else if( val>255 ) {
    return 255;
  } else {
    return (uint8_t)val;
  }
}

static uint8_t get_pixel( const uint8_t bayer[HEIGHT][WIDTH], int row, int col )
{
  if( row<0 ) {
    row = 0;
  }
  if( row>=HEIGHT ) {
    row = HEIGHT - 1;
  }
  if( col<0 ) {
    col = 0;
  }
  if( col>=WIDTH ) {
    col = WIDTH - 1;
  }
  return bayer[row][col];
}

/* RGGBパターン想定 */
void bayer_to_rgb(
  const uint8_t bayer[HEIGHT][WIDTH],
  uint8_t r_out[HEIGHT][WIDTH],
  uint8_t g_out[HEIGHT][WIDTH],
  uint8_t b_out[HEIGHT][WIDTH] )
{
  int row;
  int col;

  for( row=0; row<HEIGHT; row=row+1 ) {
    for( col=0; col<WIDTH; col=col+1 ) {
      int is_even_row;
      int is_even_col;
      int r;
      int g;
      int b;

      is_even_row = ( row%2==0 );
      is_even_col = ( col%2==0 );

      if( is_even_row&&is_even_col ) {
        /* R画素の位置 */
        r = get_pixel( bayer, row, col );
        g = ( get_pixel( bayer, row-1, col ) + get_pixel( bayer, row+1, col )
            + get_pixel( bayer, row, col-1 ) + get_pixel( bayer, row, col+1 ) ) / 4;
        b = ( get_pixel( bayer, row-1, col-1 ) + get_pixel( bayer, row-1, col+1 )
            + get_pixel( bayer, row+1, col-1 ) + get_pixel( bayer, row+1, col+1 ) ) / 4;
      } else if( is_even_row&&!is_even_col ) {
        /* G画素の位置(R行) */
        r = ( get_pixel( bayer, row, col-1 ) + get_pixel( bayer, row, col+1 ) ) / 2;
        g = get_pixel( bayer, row, col );
        b = ( get_pixel( bayer, row-1, col ) + get_pixel( bayer, row+1, col ) ) / 2;
      } else if( !is_even_row&&is_even_col ) {
        /* G画素の位置(B行) */
        r = ( get_pixel( bayer, row-1, col ) + get_pixel( bayer, row+1, col ) ) / 2;
        g = get_pixel( bayer, row, col );
        b = ( get_pixel( bayer, row, col-1 ) + get_pixel( bayer, row, col+1 ) ) / 2;
      } else {
        /* B画素の位置 */
        r = ( get_pixel( bayer, row-1, col-1 ) + get_pixel( bayer, row-1, col+1 )
            + get_pixel( bayer, row+1, col-1 ) + get_pixel( bayer, row+1, col+1 ) ) / 4;
        g = ( get_pixel( bayer, row-1, col ) + get_pixel( bayer, row+1, col )
            + get_pixel( bayer, row, col-1 ) + get_pixel( bayer, row, col+1 ) ) / 4;
        b = get_pixel( bayer, row, col );
      }

      r_out[row][col] = clamp_u8( r );
      g_out[row][col] = clamp_u8( g );
      b_out[row][col] = clamp_u8( b );
    }
  }
}

module bayer2x2_to_rgb #(
  parameter DATA_WIDTH = 8
) (
  input                       clk
 ,input                       rst_n
 ,input                       valid_in
 ,input      [DATA_WIDTH-1:0] bayer_00  // R
 ,input      [DATA_WIDTH-1:0] bayer_01  // G
 ,input      [DATA_WIDTH-1:0] bayer_10  // G
 ,input      [DATA_WIDTH-1:0] bayer_11  // B
 ,output reg                  valid_out
 ,output reg [DATA_WIDTH-1:0] r_out
 ,output reg [DATA_WIDTH-1:0] g_out
 ,output reg [DATA_WIDTH-1:0] b_out
);

  // 桁上がり保持のため1bit拡張して加算
  wire [DATA_WIDTH:0] g_sum;

  assign g_sum = bayer_01 + bayer_10;

  always @( posedge clk or negedge rst_n ) begin
    if( !rst_n ) begin
      valid_out <= 1'b0;
      r_out     <= {DATA_WIDTH{1'b0}};
      g_out     <= {DATA_WIDTH{1'b0}};
      b_out     <= {DATA_WIDTH{1'b0}};
    end else begin
      if( valid_in ) begin
        valid_out <= 1'b1;
        r_out     <= bayer_00;
        g_out     <= g_sum[DATA_WIDTH:1];
        b_out     <= bayer_11;
      end else begin
        valid_out <= 1'b0;
      end
    end
  end

endmodule

#include <stdint.h>

#define WIDTH  1920
#define HEIGHT 1080

/* WIDTHは偶数前提 */
/* BT.601フルレンジ係数の256倍スケール整数近似 */
/*   Y = ( 77R + 150G +  29B ) >> 8       */
/*   U = ( -43R - 85G + 128B ) >> 8 + 128 */
/*   V = ( 128R - 107G - 21B ) >> 8 + 128 */

static uint8_t clamp_u8( int val )
{
  if( val<0 ) {
    return 0;
  } else if( val>255 ) {
    return 255;
  } else {
    return (uint8_t)val;
  }
}

void rgb_to_yuv422(
  const uint8_t r_in[HEIGHT][WIDTH],
  const uint8_t g_in[HEIGHT][WIDTH],
  const uint8_t b_in[HEIGHT][WIDTH],
  uint8_t y_out[HEIGHT][WIDTH],
  uint8_t u_out[HEIGHT][WIDTH/2],
  uint8_t v_out[HEIGHT][WIDTH/2] )
{
  int row;
  int col;

  /* Y: 全画素で計算(+128は丸め) */
  for( row=0; row<HEIGHT; row=row+1 ) {
    for( col=0; col<WIDTH; col=col+1 ) {
      int y;

      y = ( 77 * r_in[row][col] + 150 * g_in[row][col] + 29 * b_in[row][col] + 128 ) >> 8;
      y_out[row][col] = clamp_u8( y );
    }
  }

  /* U/V: 水平2画素のRGB平均から全ラインで計算(4:2:2) */
  for( row=0; row<HEIGHT; row=row+1 ) {
    for( col=0; col<WIDTH; col=col+2 ) {
      int r_avg;
      int g_avg;
      int b_avg;
      int u;
      int v;

      r_avg = ( r_in[row][col] + r_in[row][col+1] + 1 ) / 2;
      g_avg = ( g_in[row][col] + g_in[row][col+1] + 1 ) / 2;
      b_avg = ( b_in[row][col] + b_in[row][col+1] + 1 ) / 2;

      /* 32896 = 32768(オフセット128<<8) + 128(丸め) */
      u = ( 32896 - 43 * r_avg - 85 * g_avg + 128 * b_avg ) >> 8;
      v = ( 32896 + 128 * r_avg - 107 * g_avg - 21 * b_avg ) >> 8;

      u_out[row][col/2] = clamp_u8( u );
      v_out[row][col/2] = clamp_u8( v );
    }
  }
}

module rgb_to_yuv422 #(
  parameter DATA_WIDTH = 8  // 係数と中間ビット幅は8bit前提
) (
  input                       clk
 ,input                       rst_n
 ,input                       valid_in
 ,input      [DATA_WIDTH-1:0] r_in
 ,input      [DATA_WIDTH-1:0] g_in
 ,input      [DATA_WIDTH-1:0] b_in
 ,output reg                  valid_y
 ,output reg [DATA_WIDTH-1:0] y_out
 ,output reg                  valid_uv
 ,output reg [DATA_WIDTH-1:0] u_out
 ,output reg [DATA_WIDTH-1:0] v_out
);

  reg                  phase;   // 0:水平ペアの1画素目, 1:2画素目
  reg [DATA_WIDTH-1:0] r_hold;
  reg [DATA_WIDTH-1:0] g_hold;
  reg [DATA_WIDTH-1:0] b_hold;

  wire [15:0]           y_pre;
  wire [DATA_WIDTH:0]   r_sum;
  wire [DATA_WIDTH:0]   g_sum;
  wire [DATA_WIDTH:0]   b_sum;
  wire [DATA_WIDTH-1:0] r_avg;
  wire [DATA_WIDTH-1:0] g_avg;
  wire [DATA_WIDTH-1:0] b_avg;
  wire [16:0]           u_pre;
  wire [16:0]           v_pre;

  // Y = ( 77R + 150G + 29B + 128(丸め) ) >> 8
  assign y_pre = 16'd77 * r_in + 16'd150 * g_in + 16'd29 * b_in + 16'd128;

  // 水平2画素の平均(+1は丸め、9bitで桁上がり保持)
  assign r_sum = r_hold + r_in + 1'b1;
  assign g_sum = g_hold + g_in + 1'b1;
  assign b_sum = b_hold + b_in + 1'b1;
  assign r_avg = r_sum[DATA_WIDTH:1];
  assign g_avg = g_sum[DATA_WIDTH:1];
  assign b_avg = b_sum[DATA_WIDTH:1];

  // 32896 = 32768(オフセット128<<8) + 128(丸め)
  // 定数を先に置くことで演算途中も非負となり符号なし演算で完結
  assign u_pre = 17'd32896 - 17'd43 * r_avg - 17'd85 * g_avg + 17'd128 * b_avg;
  assign v_pre = 17'd32896 + 17'd128 * r_avg - 17'd107 * g_avg - 17'd21 * b_avg;

  always @( posedge clk or negedge rst_n ) begin
    if( !rst_n ) begin
      phase    <= 1'b0;
      r_hold   <= {DATA_WIDTH{1'b0}};
      g_hold   <= {DATA_WIDTH{1'b0}};
      b_hold   <= {DATA_WIDTH{1'b0}};
      valid_y  <= 1'b0;
      y_out    <= {DATA_WIDTH{1'b0}};
      valid_uv <= 1'b0;
      u_out    <= {DATA_WIDTH{1'b0}};
      v_out    <= {DATA_WIDTH{1'b0}};
    end else begin
      // Y: 有効サイクルごとに1画素出力
      if( valid_in ) begin
        valid_y <= 1'b1;
        y_out   <= y_pre[15:8];
      end else begin
        valid_y <= 1'b0;
      end

      // U/V: 水平2画素に1回出力(4:2:2)
      if( valid_in ) begin
        if( phase==1'b0 ) begin
          r_hold   <= r_in;
          g_hold   <= g_in;
          b_hold   <= b_in;
          phase    <= 1'b1;
          valid_uv <= 1'b0;
        end else begin
          // u_pre/v_preは最大65536(17bit)となり得るため飽和処理
          if( u_pre[16] ) begin
            u_out <= {DATA_WIDTH{1'b1}};
          end else begin
            u_out <= u_pre[15:8];
          end
          if( v_pre[16] ) begin
            v_out <= {DATA_WIDTH{1'b1}};
          end else begin
            v_out <= v_pre[15:8];
          end
          phase    <= 1'b0;
          valid_uv <= 1'b1;
        end
      end else begin
        valid_uv <= 1'b0;
      end
    end
  end

endmodule
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