Grayscale image: Difference between revisions
(added ocaml) |
|||
Line 49: | Line 49: | ||
end Color; |
end Color; |
||
</ada> |
</ada> |
||
=={{header|OCaml}}== |
|||
Conversion to a grayscale image: |
|||
<ocaml>let to_grayscale ~img:(_, r_channel, g_channel, b_channel) = |
|||
let width = Bigarray.Array2.dim1 r_channel |
|||
and height = Bigarray.Array2.dim2 r_channel in |
|||
let gray_channel = |
|||
let kind = Bigarray.int8_unsigned |
|||
and layout = Bigarray.c_layout |
|||
in |
|||
(Bigarray.Array2.create kind layout width height) |
|||
in |
|||
for y = 0 to pred height do |
|||
for x = 0 to pred width do |
|||
let r = r_channel.{x,y} |
|||
and g = g_channel.{x,y} |
|||
and b = b_channel.{x,y} in |
|||
let v = (2_126 * r + 7_152 * g + 722 * b) / 10_000 in |
|||
gray_channel.{x,y} <- v; |
|||
done; |
|||
done; |
|||
(gray_channel)</ocaml> |
|||
Conversion to a color image: |
|||
<ocaml>let to_color ~img:gray_channel = |
|||
let width = Bigarray.Array2.dim1 gray_channel |
|||
and height = Bigarray.Array2.dim2 gray_channel in |
|||
let all_channels = |
|||
let kind = Bigarray.int8_unsigned |
|||
and layout = Bigarray.c_layout |
|||
in |
|||
Bigarray.Array3.create kind layout 3 width height |
|||
in |
|||
let r_channel = Bigarray.Array3.slice_left_2 all_channels 0 |
|||
and g_channel = Bigarray.Array3.slice_left_2 all_channels 1 |
|||
and b_channel = Bigarray.Array3.slice_left_2 all_channels 2 |
|||
in |
|||
Bigarray.Array2.blit gray_channel r_channel; |
|||
Bigarray.Array2.blit gray_channel g_channel; |
|||
Bigarray.Array2.blit gray_channel b_channel; |
|||
(all_channels, |
|||
r_channel, |
|||
g_channel, |
|||
b_channel)</ocaml> |
Revision as of 21:30, 7 December 2008
You are encouraged to solve this task according to the task description, using any language you may know.
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>
OCaml
Conversion to a grayscale image: <ocaml>let to_grayscale ~img:(_, r_channel, g_channel, b_channel) =
let width = Bigarray.Array2.dim1 r_channel and height = Bigarray.Array2.dim2 r_channel in
let gray_channel = let kind = Bigarray.int8_unsigned and layout = Bigarray.c_layout in (Bigarray.Array2.create kind layout width height) in for y = 0 to pred height do for x = 0 to pred width do let r = r_channel.{x,y} and g = g_channel.{x,y} and b = b_channel.{x,y} in let v = (2_126 * r + 7_152 * g + 722 * b) / 10_000 in gray_channel.{x,y} <- v; done; done; (gray_channel)</ocaml>
Conversion to a color image: <ocaml>let to_color ~img:gray_channel =
let width = Bigarray.Array2.dim1 gray_channel and height = Bigarray.Array2.dim2 gray_channel in let all_channels = let kind = Bigarray.int8_unsigned and layout = Bigarray.c_layout in Bigarray.Array3.create kind layout 3 width height in let r_channel = Bigarray.Array3.slice_left_2 all_channels 0 and g_channel = Bigarray.Array3.slice_left_2 all_channels 1 and b_channel = Bigarray.Array3.slice_left_2 all_channels 2 in Bigarray.Array2.blit gray_channel r_channel; Bigarray.Array2.blit gray_channel g_channel; Bigarray.Array2.blit gray_channel b_channel; (all_channels, r_channel, g_channel, b_channel)</ocaml>