How to convert a grey-scale image into a reverse binary image

I have images like the one shown above and I want to convert the image to a binary image where the black parts are white and the rest of the image is black. How would I approach solving this problem?

Answer 1

[Walter Roberson]

Rbin = YourImage <= 42;

[Hardit Singh]

Does not work.

[Walter Roberson]

I assure you that it does work, with the exception of TIFF images that use IEEE floating point representation (these exist but are rare)

Answer 2

[Image Analyst]

Try this:

grayImage = 255 - grayImage; % Assuming your image is uint8.  Use 65535 if it's uint16.