RGB-HSI,HSI-RGB
HSI----->>>RGB:
-
function
rgb = hsi2rgb(hsi)
-
%HSI2RGB Converts an HSI image
to
RGB.
-
%
RGB = HSI2RGB(HSI) converts an HSI image
to
RGB, where HSI
is
-
% assumed
to be of
class double
with:
-
% hsi(:, :,
1) = hue image, assumed
to be
in the range
-
% [
0,
1] by having been divided by
2*pi.
-
% hsi(:, :,
2) = saturation image,
in the range [
0,
1].
-
% hsi(:, :,
3) = intensity image,
in the range [
0,
1].
-
%
-
% The components of the output image are:
-
%
rgb(:, :,
1) = red.
-
%
rgb(:, :,
2) = green.
-
%
rgb(:, :,
3) = blue.
-
% Copyright
2002
-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins
-
% Digital Image Processing Using MATLAB, Prentice-Hall,
2004
-
% $Revision:
1.5 $ $
Date:
2003/
10/
13
01:
01:
06 $
-
% Extract the individual HSI component images.
-
H = hsi(:, :,
1) *
2 * pi;
-
S = hsi(:, :,
2);
-
I = hsi(:, :,
3);
-
% Implement the conversion equations.
-
R = zeros(size(hsi,
1), size(hsi,
2));
-
G = zeros(size(hsi,
1), size(hsi,
2));
-
B = zeros(size(hsi,
1), size(hsi,
2));
-
% RG sector (
0 <= H <
2*pi/
3).
-
idx = find( (
0 <= H) & (H <
2*pi/
3));
-
B(idx) = I(idx) .* (
1 - S(idx));
-
R(idx) = I(idx) .* (
1 + S(idx) .*
cos(H(idx)) ./
cos(pi/
3 - H(idx)));
-
G(idx) =
3*I(idx) - (R(idx) + B(idx));
-
% BG sector (
2*pi/
3 <= H <
4*pi/
3).
-
idx = find( (
2*pi/
3 <= H) & (H <
4*pi/
3) );
-
R(idx) = I(idx) .* (
1 - S(idx));
-
G(idx) = I(idx) .* (
1 + S(idx) .*
cos(H(idx) -
2*pi/
3) ./
cos(pi - H(idx)));
-
B(idx) =
3*I(idx) - (R(idx) + G(idx));
-
% BR sector.
-
idx = find( (
4*pi/
3 <= H) & (H <=
2*pi));
-
G(idx) = I(idx) .* (
1 - S(idx));
-
B(idx) = I(idx) .* (
1 + S(idx) .*
cos(H(idx) -
4*pi/
3) ./
cos(
5*pi/
3 - H(idx)));
-
R(idx) =
3*I(idx) - (G(idx) + B(idx));
-
% Combine all three results into an
RGB image. Clip
to [
0,
1]
to
-
% compensate
for floating-point arithmetic rounding effects.
-
rgb = cat(
3, R, G, B);
-
rgb = max(min(
rgb,
1),
0);
-
-
RGB---->>HSI
-
function hsi = rgb2hsi(rgb)
-
%RGB2HSI Converts an RGB image
to HSI.
-
% HSI = RGB2HSI(RGB) converts an RGB image
to HSI. The input image
-
%
is assumed
to be
of size M-
by-N-
by
-3,
where the third dimension
-
% accounts
for three image planes: red, green,
and blue,
in that
-
%
order.
If all RGB component images are equal, the HSI conversion
-
%
is undefined. The input image can be
of
class
double (
with values
-
%
in the range [
0,
1]), uint8,
or uint16.
-
%
-
% The output image, HSI,
is
of
class
double,
where:
-
% hsi(:, :,
1) = hue image normalized
to the range [
0,
1]
by
-
% dividing all angle values
by
2*pi.
-
% hsi(:, :,
2) = saturation image,
in the range [
0,
1].
-
% hsi(:, :,
3) = intensity image,
in the range [
0,
1].
-
-
% Copyright
2002
-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins
-
% Digital Image Processing
Using MATLAB, Prentice-Hall,
2004
-
% $Revision:
1.4 $ $
Date:
2003/
09/
29
15:
21:
54 $
-
-
% Extract the individual component immages.
-
rgb = im2double(rgb);
-
r = rgb(:, :,
1);
-
g = rgb(:, :,
2);
-
b = rgb(:, :,
3);
-
-
% Implement the conversion equations.
-
num =
0.5*((r - g) + (r - b));
-
den = sqrt((r - g).^
2 + (r - b).*(g - b));
-
theta = acos(num./(den + eps));
-
-
H = theta;
-
H(b > g) =
2*pi - H(b > g);
-
H = H/(
2*pi);
-
-
num = min(min(r, g), b);
-
den = r + g + b;
-
den(den ==
0) = eps;
-
S =
1 -
3.* num./den;
-
-
H(S ==
0) =
0;
-
-
I = (r + g + b)/
3;
-
-
% Combine all three results
into an hsi image.
-
hsi = cat(
3, H, S, I);