I want to change the gray scale from [0 1] to [0 500]

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Anvinder Singh 2016-3-12

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评论： Image Analyst 2016-3-13

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I want to change the gray scale from [0 1] to [0 500] and have used the following functions

b= imadjust(a,[0; 1],[0; 500])

and

%j = imadjust(a,stretchlim(a),[0 500]);

but they don't seem to work. There are errors when i plot them.

CODE:

 a = ones(256, 256, 3);
 a(10:110,40:100,:)=0;
 a(120:200,120:200,:)=0;
 %colormap('gray');
 image(a)
 figure();
 b= imadjust(a,[0; 1],[0; 500])
 %j = imadjust(a,stretchlim(a),[0 500]);
 image(b)

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回答（2 个）

Walter Roberson 2016-3-12

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"By default, the CDataMapping property for the image is set to 'direct' so image interprets values in C as indices into the colormap. For example, the bottom right pixel corresponding to the last element in C, 22, uses the 22nd color of the colormap."

Do you have 500 colors or more in your colormap?

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Anvinder Singh 2016-3-12

Walter, the imagesc doesnt work. The error i get is "Error in imadjust (line 99) validateLowHigh(lowIn,highIn,lowOut,highOut);"

Walter Roberson 2016-3-12

Then that was not errors when you plot them, that was errors when you did the adjustment. And you did not post the complete error message.

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Image Analyst 2016-3-12

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编辑：Image Analyst 2016-3-13

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How about using mat2gray():

b = 500 * mat2gray(a);

It scales min to max, whereas imadjust() scales based on percentage of counts in the histogram tails. Just depends on what you want to do.

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Image Analyst 2016-3-13

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Come on. It does not. Here's a full blown demo:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Make all white.
grayImage = ones(256, 256);
% Make some rectangles black.
grayImage(10:110,40:100) = 0;
grayImage(120:200,120:200) = 0;
subplot(3, 1, 1);
imshow(grayImage);
axis on;
colormap(gray(500));
colorbar;
title('Original Image', 'FontSize', fontSize);
% Scale the image intensity to between 0 and 500
scaledImage = 500*mat2gray(grayImage);
subplot(3, 1, 2);
imshow(scaledImage, []);
axis on;
colormap(gray(500));
colorbar;
title('Scaled Image', 'FontSize', fontSize);
% Make noisy image where lambda is the value of the image at that location
noisyImage = poissrnd(scaledImage);
subplot(3, 1, 3);
imshow(noisyImage, []);
title('Noisy Image', 'FontSize', fontSize);
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')

Anvinder Singh 2016-3-13

Oh, Thanks Image analyst. Just forgot it will have no poisson noise for '0' value. It seems to be good. One last thing, if i need the background to be white i am trying to change "grayimage = ones(256, 256);" and grayscale value but it doesnt seem to show up ?