Смешать два цвета с использованием коэффициента прозрачности

// This function mixes two bytes According to value of TRANS 
// The value of TRANS is between 0 (result then will be equal to FG) 
// and 255 (result then will be equal to BG) 
function
 MixBytes(FG, BG, TRANS: byte): byte;
 asm

   push bx  // push some regs 
  push cx
   push dx
   mov DH,TRANS // remembering Transparency value (or Opacity - as you like) 
  mov BL,FG    // filling registers with our values 
  mov AL,DH    // BL = ForeGround (FG) 
  mov CL,BG    // CL = BackGround (BG) 
  xor
 AH,AH    // Clear High-order parts of regs 
  xor
 BH,BH
   xor
 CH,CH
   mul BL       // AL=AL*BL 
  mov BX,AX    // BX=AX 
  xor
 AH,AH
   mov AL,DH
   xor
 AL,$FF   // AX=(255-TRANS) 
  mul CL       // AL=AL*CL 
  add AX,BX    // AX=AX+BX 
  shr
 AX,8     // Fine! Here we have mixed value in AL 
  pop dx       // Hm... No rubbish after us, ok? 
  pop cx
   pop bx       // Bye, dear Assembler - we go home to Delphi! 
end
;

 // Here we mix R,G and B channels of our colors separately. 
// The value of T is between 0 and 255 as described above. 

// As you know, TColor value is 4 bytes length integer value where 
// low byte is red channel, 2nd byte is green and 3rd byte is blue 

function
 MixColors(FG, BG: TColor; T: byte): TColor;
 var
 r,g,b:byte;
 begin

   R := MixBytes(FG and
 255,BG and
 255,T); // extracting and mixing Red 
  G := MixBytes((FG shr
 8) and
 255,(BG shr
 8) and
 255,T); // the same with green 
  B := MixBytes((FG shr
 16) and
 255,(BG shr
 16) and
 255,T); // and blue, of course 
  Result := r+g*256+b*65536; // finishing with combining all channels together 
end
;

Другое по теме:

• Работа с палитрой
• Перевод RGB в GRAY
• Преобразование цвета RGB 34 HLS