How do I change an image to binary?

I have a picture of a black wrench with a gray background. I need to figure out a threshold value that separates the two so that I can set the background pixels to 0 and the pixels of the wrench to 1. I just need help figuring out the threshold value and extract the background pixels vs. the wrench pixels. I think I can figure out how to then change them to either 1 or 0.

Answer 1

[Star Strider]

See the im2bw function in the Image Processing Toolbox. Experiment until you get the result you want.

[anibb]

Unfortunately i'm not able to use a built-in function such as im2bw

[Star Strider]

Without your image to work from, I can only guess at a solution. A grayscale image (that I assume you have) is a 2D matrix and has unit8 values from 0 to 255. You may have to ‘cut and try’, not uncommon with any signal processing problem.

Start with something like:

BinImg = GrayImg >127;

then display it with imshow to see the result. Then just vary the threshold up or down until you get the result you want.

Answer 2

[Ahmet Cecen]

ImageSegmenter should help you if you have the toolbox, since you sound like a novice user. http://www.mathworks.com/help/images/image-segmentation-using-the-image-segmenter-app.html

Otherwise use the histogram function. If you are lucky, it will be shaped like the back of a camel and you can find a valley between to peaks, then use that value as your threshold. http://www.mathworks.com/help/matlab/ref/histogram.html

There is also a function that finds an automatic threshold for you if you trust it, but it also requires the toolbox: http://www.mathworks.com/help/images/ref/graythresh.html

Answer 3

[Walter Roberson]

pixvals = sort(YourGreyImage(:));
middle_value = pixvals(round(end/2));
BWimage = YourGreyImage < middle_value;