Grayscale image
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Many image processing algorithms are defined for grayscale (or else monochromatic) images. Extend the data storage type defined on this page to support grayscale images. Define two operations, one to convert a color image to a grayscale image and one for the backward conversion. To get luminance of a color use the formula recommended by CIE:
L = 0.2126·R + 0.7152·G + 0.0722·B
When using floating-point arithmetic make sure that rounding errors would not cause run-time problems or else distorted results when calculated luminance is stored as an unsigned integer.
Ada
<ada> type Grayscale_Image is array (Positive range <>, Positive range <>) of Luminance; </ada> Conversion to a grayscale image: <ada> function Grayscale (Picture : Image) return Grayscale_Image is
type Extended_Luminance is range 0..10_000_000; Result : Grayscale_Image (Picture'Range (1), Picture'Range (2)); Color : Pixel;
begin
for I in Picture'Range (1) loop
for J in Picture'Range (2) loop
Color := Picture (I, J);
Result (I, J) :=
Luminance
( Extended_Luminance'Min
( Extended_Luminance (Luminance'Last),
( ( 2_126 * Extended_Luminance (Color.R)
+ 7_152 * Extended_Luminance (Color.G)
+ 722 * Extended_Luminance (Color.B)
)
/ 10_000
) ) );
end loop;
end loop;
return Result;
end Grayscale; </ada> Conversion to a color image: <ada> function Color (Picture : Grayscale_Image) return Image is
Result : Image (Picture'Range (1), Picture'Range (2));
begin
for I in Picture'Range (1) loop
for J in Picture'Range (2) loop
Result (I, J) := (others => Picture (I, J));
end loop;
end loop;
return Result;
end Color; </ada>