IMAGE_THRESHOLD
Black/White Version of Grayscale Image

IMAGE_THRESHOLD is a MATLAB function which creates a black and white version of a grayscale image by specifying a single threshold value; pixels below this value become black, and above this value they are white.

Usage:

function bw = image_threshold ( gray, a )

• gray is an m by n uint8 (short integers, 0 to 255) array containing the grayscale image data; MATLAB's imread() command can be used to create such a dataset from a graphics image file.
• a is a value between 0 and 255 which is used for thresholding.
• bw is an m by n uint8 array containing the gray scale version of the thresholded image. All values in this array are 0 or 255.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Related Data and Programs:

IMAGE_CONTRAST, a MATLAB program which applies image processing techniques to increase the contrast in an image.

IMAGE_DENOISE, a MATLAB library which applies image processing techniques to remove noise from an image.

IMAGE_DIFFUSE, a MATLAB library which uses diffusion to smooth out an image.

IMAGE_EDGE, a MATLAB program which demonstrates a simple technique for edge detection in an image.

IMAGE_NOISE, a MATLAB library which adds noise to an image.

IMAGE_QUANTIZATION, a MATLAB library which demonstrates how the KMEANS algorithm can be used to reduce the number of colors or shades of gray in an image.

IMAGE_RGB_TO_GRAY, a MATLAB function which creates a grayscale version of an RGB image.

Reference:

MathWorks documentation for the Image Processing Toolbox is available at http://www.mathworks.com/access/helpdesk/help/pdf_doc/images/images_tb.pdf.

• Jonas Gomes, Luiz Velho,
  Image Processing for Computer Graphics,
  Springer, 1997,
  ISBN: 0387948546,
  LC: T385.G65.
• William Pratt,
  Digital Image Processing,
  Second Edition,
  Wiley, 1991,
  ISBN13: 978-0471857662,
  LC: TA1632.P7.

Source Code:

• image_threshold.m, sets pixels less than or equal to A to black, and pixels greater than A to white.
• image_threshold2.m, sets pixels less than A to black, and pixels greater than B to white, leaving intermediate pixels unchanged.
• image_threshold3.m, sets pixels less than A or greater than B to white, leaving intermediate pixels unchanged.

Examples and Tests:

CONJUNCTION is an astronomical image.

• conjunction_gray.png, the grayscale image.
• conjunction_bw_050.png, a version of the image using a threshold of 50.
• conjunction_bw_100.png, a version of the image using a threshold of 100.

STAR_FIELD is an astronomical image.

• star_field_gray.png, the grayscale image.
• star_field_bw_050.png, a version of the image using a threshold of 50.
• star_field_bw_100.png, a version of the image using a threshold of 100.
• star_field_bw_150.png, a version of the image using a threshold of 150.
• star_field_bw_200.png, a version of the image using a threshold of 200.
• star_field_bw_250.png, a version of the image using a threshold of 250.

You can go up one level to the MATLAB source codes.