How to change all the colours in the image to black

how to change all the colours in the image to black except the white colour in image?

Answer 1

[Timo Dietz]

Try this:

imageData = imread([yourFile]);

% split R, G, B
imgR = imageData(:, :, 1);
imgG = imageData(:, :, 2);
imgB = imageData(:, :, 3);

% get linear index of all pixels with color not white 
colIdx = (imgR < 1 | imgG < 1 | imgB < 1);

% change color to black
imgR(colIdx) = 0;
imgG(colIdx) = 0;
imgB(colIdx) = 0;

% write back to new image data or overwrite the origin imageData
newImage(:, :, 1) = imgR;
newImage(:, :, 2) = imgG;
newImage(:, :, 3) = imgB;

Answer 2

[yanqi liu]

clc; clear all; close all;
I = imread('ceshi.png');
I2 = rgb2hsv(I);
s = mat2gray(I2(:,:,2));
bw = im2bw(s, 0.5);
figure; imshow(~bw)