IMAGE_RGB_TO_GRAY
Grayscale Version of RGB Image

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

An RGB image is an (M,N,3) array.

A grayscale image is an (M,N) array.

A grayscale version of an RGB image can be made by averaging the RGB components of each pixel.

A more sophisticated approach uses the luminance function:

        GRAY = 0.2126 * R + 0.7152 * G + 0.0722 * B
      

Usage:

function gray = rgb_to_gray ( rgb, equal )

• rgb is an m by n by 3 uint8 (short integers, 0 to 255) array containing the RGB image data; MATLAB's imread() command can be used to create such a dataset from a graphics image file.
• equal is 1 if the R, G and B values are to be weighted equally. Otherwise, a luminance function is used which accounts for the different contributions of each channel to brightness.
• gray is an m by n uint8 array containing the gray scale version of the image.

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 program which applies image processing techniques to remove noise from an image.

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

IMAGE_NOISE, MATLAB programs which add 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_THRESHOLD, a MATLAB library 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.

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:

• rgb_to_gray.m, creates a grayscale version of an RGB image.

Examples and Tests:

CONJUNCTION is an astronomical image.

• conjunction.png, the RGB image.
• conjunction_gray.png, a grayscale version of the image, using nonequal RGB weighting.

STAR_FIELD is an astronomical image.

• star_field.png, the RGB image.
• star_field_gray.png, a grayscale version of the image, using nonequal RGB weighting.
• star_field_gray_equal.png, a grayscale version of the image, using equal RGB weighting.

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