www.gusucode.com > matlab非局部均值工具箱 > matlab非局部均值工具箱/matlab非局部均值工具箱/toolbox_nlmeans/toolbox/perform_histogram_equalization.m
function x = perform_histogram_equalization(x,y,options)
% perform_histogram_equalization - perform histogram equalization
%
% x = perform_histogram_equalization(x,y,options);
%
% Change the values of x so that its ordered values match
% the ordered values of y.
%
% You can set
% options.cols=1 to operate along columns
% options.rows=1 to operate along rows
% options.absval to operate only on absolute values.
%
% Copyright (c) 2006 Gabriel Peyr?
options.null = 0;
if isfield(options ,'absval')
absval = options.absval;
else
absval = 0;
end
if isfield(options ,'cols')
cols = options.cols;
else
cols = 0;
end
if isfield(options ,'rows')
rows = options.rows;
else
rows = 0;
end
if isfield(options, 'match_ycbcr')
match_ycbcr = options.match_ycbcr;
else
match_ycbcr = 1;
end
% for color images
if size(x,3)>1
if size(x,3)~=size(y,3)
error('x and y images must have the same number of components.');
end
if size(x,3)==3 && match_ycbcr
x = rgb2ycbcr(x);
y = rgb2ycbcr(y);
end
% match each color
for i=1:3
x(:,:,i) = perform_histogram_equalization(x(:,:,i), y(:,:,i), options);
end
if size(x,3)==3 && match_ycbcr
x = ycbcr2rgb(x);
end
return;
end
if cols && rows
error('You cannote specify both cols and rows');
end
if cols && size(x,2)>1
if not(size(x,2)==size(y,2))
error('x and y must have same number of columns');
end
for i=1:size(x,2)
x(:,i) = perform_histogram_equalization(x(:,i),y(:,i),options);
end
return;
end
if rows && size(x,1)>1
if not(size(x,1)==size(y,1))
error('x and y must have same number of rows');
end
for i=1:size(x,1)
x(i,:) = perform_histogram_equalization(x(i,:),y(i,:),options);
end
return;
end
sx = size(x);
x = x(:);
y = y(:);
if absval
s = sign(x);
x = abs(x);
y = abs(y);
end
[vx,Ix] = sort(x);
[vy,Iy] = sort(y);
nx = length(x);
ny = length(y);
ax = linspace(1,ny,nx);
ay = 1:ny;
vx = interp1(ay,vy,ax);
x(Ix) = vx;
if absval
x = x .* s;
end
x = reshape(x,sx);
function rgb = ycbcr2rgb(in)
%YCBCR2RGB Convert YCbCr values to RGB color space.
% RGBMAP = YCBCR2RGB(YCBCRMAP) converts the YCbCr values in the
% colormap YCBCRMAP to the RGB color space. If YCBCRMAP is M-by-3 and
% contains the YCbCr luminance (Y) and chrominance (Cb and Cr) color
% values as columns, then RGBMAP is an M-by-3 matrix that contains
% the red, green, and blue values equivalent to those colors.
%
% RGB = YCBCR2RGB(YCBCR) converts the YCbCr image to the equivalent
% truecolor image RGB.
%
% Class Support
% -------------
% If the input is a YCbCr image, it can be of class uint8, uint16,
% or double; the output image is of the same class as the input
% image. If the input is a colormap, the input and output
% colormaps are both of class double.
%
% Example
% -------
% Convert image from RGB space to YCbCr space and back.
%
% rgb = imread('board.tif');
% ycbcr = rgb2ycbcr(rgb);
% rgb2 = ycbcr2rgb(ycbcr);
%
% See also NTSC2RGB, RGB2NTSC, RGB2YCBCR.
% Copyright 1993-2003 The MathWorks, Inc.
% $Revision: 1.15.4.2 $ $Date: 2003/08/23 05:54:51 $
% Reference:
% Charles A. Poynton, "A Technical Introduction to Digital Video",
% John Wiley & Sons, Inc., 1996
%initialize variables
isColormap = false;
classin = class(in);
%must reshape colormap to be m x n x 3 for transformation
if (ndims(in)==2)
%colormap
isColormap=true;
colors = size(in,1);
in = reshape(in, [colors 1 3]);
end
%initialize output
rgb = in;
% set up constants for transformation. T alone will transform YCBCR in [0,255]
% to RGB in [0,1]. We must scale T and the offsets to get RGB in the appropriate
% range for uint8 and for uint16 arrays.
T = [65.481 128.553 24.966;...
-37.797 -74.203 112; ...
112 -93.786 -18.214];
Tinv = T^-1;
offset = [16;128;128];
Td = 255 * Tinv;
offsetd = Tinv * offset;
T8 = Td;
offset8 = T8 * offset;
T16 = (65535/257) * Tinv;
offset16 = 65535 * Tinv * offset;
switch classin
case 'double'
for p = 1:3
rgb(:,:,p) = Td(p,1) * in(:,:,1) + Td(p,2) * in(:,:,2) + ...
Td(p,3) * in(:,:,3) - offsetd(p);
end
case 'uint8'
for p = 1:3
rgb(:,:,p) = imlincomb(T8(p,1),in(:,:,1),T8(p,2),in(:,:,2), ...
T8(p,3),in(:,:,3),-offset8(p));
end
case 'uint16'
for p = 1:3
rgb(:,:,p) = imlincomb(T16(p,1),in(:,:,1),T16(p,2),in(:,:,2), ...
T16(p,3),in(:,:,3),-offset16(p));
end
end
if isColormap
rgb = reshape(rgb, [colors 3 1]);
end
if isa(rgb,'double')
rgb = min(max(rgb,0.0),1.0);
end
%%%
%Parse Inputs
%%%
function X = parse_inputs(varargin)
checknargin(1,1,nargin,mfilename);
X = varargin{1};
if ndims(X)==2
checkinput(X,{'uint8','uint16','double'},'real nonempty',mfilename,'MAP',1);
if (size(X,2) ~=3 || size(X,1) < 1)
eid = sprintf('Images:%s:invalidSizeForColormap',mfilename);
msg = 'MAP must be a m x 3 array.';
error(eid,'%s',msg);
end
elseif ndims(X)==3
checkinput(X,{'uint8','uint16','double'},'real',mfilename,'RGB',1);
if (size(X,3) ~=3)
eid = sprintf('Images:%s:invalidTruecolorImage',mfilename);
msg = 'RGB must a m x n x 3 array.';
error(eid,'%s',msg);
end
else
eid = sprintf('Images:%s:invalidInputSize',mfilename);
msg = ['RGB2GRAY only accepts two-dimensional or three-dimensional ' ...
'inputs.'];
error(eid,'%s',msg);
end
function out = rgb2ycbcr(in)
%RGB2YCBCR Convert RGB values to YCBCR color space.
% YCBCRMAP = RGB2YCBCR(MAP) converts the RGB values in MAP to
% the YCBCR color space. YCBCRMAP is a M-by-3 matrix that contains
% the YCBCR luminance (Y) and chrominance (Cb and Cr) color values as
% columns. Each row represents the equivalent color to the
% corresponding row in the RGB colormap.
%
% YCBCR = RGB2YCBCR(RGB) converts the truecolor image RGB to the
% equivalent image in the YCBCR color space.
%
% Class Support
% -------------
% If the input is an RGB image, it can be of class uint8, uint16,
% or double; the output image is of the same class as the input
% image. If the input is a colormap, the input and output colormaps
% are both of class double.
%
% Examples
% --------
% Convert RGB image to YCbCr.
%
% RGB = imread('board.tif');
% YCBCR = rgb2ycbcr(RGB);
%
% Convert RGB color space to YCbCr.
%
% map = jet(256);
% newmap = rgb2ycbcr(map);
% See also NTSC2RGB, RGB2NTSC, YCBCR2RGB.
% Copyright 1993-2003 The MathWorks, Inc.
% $Revision: 1.13.4.2 $ $Date: 2003/08/23 05:54:37 $
% Reference:
% C.A. Poynton, "A Technical Introduction to Digital Video", John Wiley
% & Sons, Inc., 1996, p. 175
%initialize variables
isColormap = false;
classin = class(in);
%must reshape colormap to be m x n x 3 for transformation
if (ndims(in)==2)
%colormap
isColormap=true;
colors = size(in,1);
in = reshape(in, [colors 1 3]);
end
% set up constants for transformation
T = [65.481 128.553 24.966;...
-37.797 -74.203 112; ...
112 -93.786 -18.214];
offset = [16;128;128];
offset16 = 257 * offset;
fac8 = 1/255;
fac16 = 257/65535;
%initialize output
out = in;
% do transformation
switch classin
case 'uint8'
for p=1:3
out(:,:,p) = imlincomb(T(p,1)*fac8,in(:,:,1),T(p,2)*fac8,in(:,:,2),...
T(p,3)*fac8,in(:,:,3),offset(p));
end
case 'uint16'
for p=1:3
out(:,:,p) = imlincomb(T(p,1)*fac16,in(:,:,1),T(p,2)*fac16,in(:,:,2),...
T(p,3)*fac16,in(:,:,3),offset16(p));
end
case 'double'
% These equations transform RGB in [0,1] to YCBCR in [0, 255]
for p=1:3
out(:,:,p) = T(p,1) * in(:,:,1) + T(p,2) * in(:,:,2) + T(p,3) * ...
in(:,:,3) + offset(p);
end
out = out / 255;
end
if isColormap
out = reshape(out, [colors 3 1]);
end