MATLAB: Does RGB2HSV return an incorrect result for double images in MATLAB 7.7(R2008b)

doubleimagesMATLABrgb2hsv

When I used rgb2hsv on a double image, I expected return numbers of less than or equal to 1.0.
For example, the following code snippet results in [0.0370 0.5385 117.0000] whereas I expected [0.0370 0.5385 0.4588].
Reproduction steps:
   x=[117,68,54]
class(x)
rgb2hsv(x)

Best Answer

This is an expected behavior in MATLAB 7.7 (R2008b) in the way the function RGB2HSV handles double images.
The reason is as follows:
When working with images, MATLAB assumes that if the datatype of the image is double then the range of input values are from 0 to 1. So in the case where the input x is double, one should scale the inital vector [117,68,54] by 255 to get the correct answers.
x=[117,68,54]/255
rgb2hsv(x)
For more information on 8-bit and 16-bit image handling in MATLAB, please refer the following:
 <http://www.mathworks.com/access/helpdesk/help/techdoc/creating_plots/f2-1667.html>
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