Create histogram to determine the threshold value to use [image processing]

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Esther
Esther 2012-10-1
编辑： Vedpal Singh 2016-10-7
Hi. as above question mentioned. I want to know how do i determine the threshold value to use. probably creating histogram? how do i do it? thanks!:)
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ANCHIT
ANCHIT 2014-6-9
hii all as the question asked thresholding by histogram I have an RGB Image of a graph paper from which I want to xtract the data wwhat is the best way of doing the thresholding. please explain me thanks

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回答（3 个）

Image Analyst
Image Analyst 2012-10-1
Isn't it 42? If not, then how about the threshold given by
normalizedThreshold = graythresh(grayImage);
That uses the famous Otsu method, which is sometimes okay for certain kinds of images, but rarely good (it seems like) for yours and mine. There are lots of methods: http://fiji.sc/wiki/index.php/Auto_Threshold. I really like the triangle method best. It's useful in lots of particle sizing/blob detection situations. It basically draws a line from the peak to the baseline of your histogram. Then it extends a line perpendicular to that. The perpendicular line that hits the histogram that is the longest indicates the threshold to use. In other words, it finds the "corner" at the base of the histogram. It's really good for skewed histograms, which are quite common.
Which thresholding method is best for you depends on your image and what you say is the best. Upload your image so we can see it. Try tinypic.com.
Mahua Nandy(Pal)
Mahua Nandy(Pal) 2012-10-1
编辑：Walter Roberson 2012-10-2
I = imread('coins.png');
level = graythresh(I);
BW = im2bw(I,level);
figure, imshow(BW)
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Image Analyst
Image Analyst 2016-4-10
Yes, but there's a fair chance that level is no good. im2bw works well for high contrast images with a nicely bimodal histogram. You may need a different algorithm. You can use my manual, interactive thresholding app to try to decide which threshold is best for your type of images. http://www.mathworks.com/matlabcentral/fileexchange/29372-thresholding-an-image

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Vedpal Singh
Vedpal Singh 2016-10-7
编辑：Vedpal Singh 2016-10-7
Hi Esther, You can use the imthresh method to determine the threshold value of an image. The code of imthresh is available here: https://searchcode.com/codesearch/view/13889967/
In addition, you can try im2bw, but it's not a better option, because its good for high contrast images.

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