im2gray
Syntax
Description
converts
the specified truecolor image I
= im2gray(RGB
)RGB
to a grayscale intensity image
I
. The im2gray
function accepts grayscale images
as inputs and returns them unmodified.
The im2gray
function converts RGB images to grayscale by eliminating
the hue and saturation information while retaining the luminance.
Examples
Input Arguments
Output Arguments
Tips
The
im2gray
function is identical torgb2gray
except that it can accept grayscale images as inputs, returning them unmodified. Thergb2gray
function returns an error if the input image is a grayscale image. If you use theim2gray
function, code like this loop is no longer necessary.if ndims(I) == 3 I = rgb2gray(I); end
Unlike the
rgb2gray
function, theim2gray
function does not accept colormaps as an input. To convert a colormap to grayscale, use thecmap2gray
function.
Algorithms
The im2gray
function converts RGB values to grayscale values by forming
a weighted sum of the R, G, and B
components:
0.2989 * R + 0.5870 * G + 0.1140 * B
These are the same weights used by the rgb2ntsc
(Image Processing Toolbox) function to compute the Y component.
The coefficients used to calculate grayscale values in the im2gray
function are identical to those used to calculate luminance (E'y) in Rec.ITU-R BT.601-7 after
rounding to three decimal places.
Rec.ITU-R BT.601-7 calculates E'y using the following formula:
0.299 * R + 0.587 * G + 0.114 * B
Extended Capabilities
Version History
Introduced in R2020b