map from value to colormap

Question

Guy Eyal 2014-7-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/144231-map-from-value-to-colormap

编辑： KSSV 2020-6-23

I use pcolor to create a figure out of some matrix of data.

h=pcolor(X,Y,M);

Is it possible to receive for a specific index in the matrix in which color (RGB values) pcolor used (assuming a constant colormap)?

Or should i ask it - If I have a colormap and caxis - is there any function that will give me the color of a value (mapping from value to rgb value in the colormap)?

Thanks

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Answer 1

Arun Mathew Iype 2014-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/144231-map-from-value-to-colormap#answer_147015

在 MATLAB Online 中打开

Please check the solution provided at the below link by Jason D. Yeatman which does the exact thing that you want http://web.stanford.edu/~jyeatman/AFQ/doc/utilities/vals2colormap.html#_top

function rgb = vals2colormap(vals, colormap, crange)
% Take in a vector of N values and return and return a Nx3 matrix of RGB
% values associated with a given colormap
%
% rgb = AFQ_vals2colormap(vals, [colormap = 'jet'], [crange])
%
% Inputs:
% vals     = A vector of values to map to a colormap or a cell array of
%            vectors of values
% colormap = A matlab colormap. Examples: colormap = 'autumn';
%            colormap = 'jet'; colormap = 'hot';
% crange   = The values to map to the minimum and maximum of the colormap.
%            Defualts to the full range of values in vals.
%
% Outputs:
% rgb      = Nx3 matrix of rgb values mapping each value in vals to the
%            corresponding rgb colors.  If vals is a cell array then rgb
%            will be a cell array of the same length
%
% Example:
% vals = rand(1,100);
% rgb = AFQ_vals2colormap(vals, 'hot');
%
% Copyright Jason D. Yeatman, June 2012

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Hamidreza Heydarian 2019-1-12

编辑：KSSV 2020-6-23

The link is dead!

New link:

https://github.com/vistalab/vistateach/blob/master/cogneuro/tutorial1_timeseries/vals2colormap.m

Image Analyst 2019-1-12

编辑：Image Analyst 2019-1-12

在 MATLAB Online 中打开

Maybe not a bad thing considering the bad programming practices they used. For example, calling an input argument colormap when colormap is the name of a built in function. So how can you use the colormap function to get the arrays? I'm almost certain you can't do

cmap = colormap(colormap);

Assuming you just put in the string directly, you can probably do pretty much the same thing by doing this:

grayImage = imread('pout.tif');
subplot(2,2,1);
imshow(grayImage);
fontSize = 14;
title('Gray Scale Image', 'FontSize', fontSize);
subplot(2,2,2);
imhist(grayImage);
grid on;
title('Histogram', 'FontSize', fontSize);
% Define range of gray levels that the colormap should go between.
grayLevelRange = [75, 150]; % Whatever you want.
cmap = jet(256);
% Specify color for gray levels below the specified range.
cmap1 = repmat(cmap(1,:), [grayLevelRange(1), 1]);
% Let the middle part be remapped such that the full colormap
% covers the specified gray level range.
cmap2 = imresize(cmap, [abs(grayLevelRange(2) - grayLevelRange(1) + 1), 3]);
% Specify color for gray levels above the specified range.
cmap3 = repmat(cmap(end, :), [255 - grayLevelRange(2), 1]);
% Combine to form a new colormap.
cmap = [cmap1; cmap2; cmap3];
% Apply the colormap to the gray scale image to form an RGB image.
rgbImage = ind2rgb(grayImage, cmap);
% Display the RGB image.
subplot(2, 2, 3);
imshow(rgbImage);
title('RGB Color-Mapped Image', 'FontSize', fontSize);