Importing Image for Colour Conversion

Hi there,

I'm trying to use the colorspace transformation, which can be found here http://www.mathworks.com/matlabcentral/fileexchange/28790-colorspace-transformations

Here's the basic info on the function:

function varargout = colorspace(Conversion,varargin)
%COLORSPACE  Transform a color image between color representations.
%   B = COLORSPACE(S,A) transforms the color representation of image A
%   where S is a string specifying the conversion.  The input array %A should be a real full double array of size Mx3 or MxNx3.  The % output B is the same size as A.
%
%   S tells the source and destination color spaces, S = 'dest<-src', or 
%   alternatively, S = 'src->dest'.  
%
%  All conversions assume 2 degree observer and D65 illuminant.

So I've been trying to do this:

colour_wheel_lab = colorspace('hsv<-lab', colour_wheel)

But I keep getting error messages claiming there is an error when it gets to the source image Ii.e. image 'A' or the 'colour_wheel'). I've been loading the source image using 'imread' but I'm not sure if this puts it into the correct format for this function. Any ideas here? Do I need to convert the image into a different array?

Thanks in advance!

Answer 1

[Walter Roberson]

Notice that A should be "a real full double array". If you are using imread() then you are probably getting an uint8 image. Use im2double() to convert it.

[Image Analyst]

He has an LAB image so he's already converted the RGB image into LAB, but that can be either integer or double depending on how he obtained it. I think if you used the built-in MATLAB color conversion function, makecform, then you can get either an integer LAB out, if you passed in uint8, or you can get a floating point lab image, if you passed in a floating point image. The range of the L, A, and B also varies depending on what you passed in, integers or doubles, and I'm not sure any of them are what you'd get out of a spectrophotometer or colorimeter. I'm not sure what he'd get for lab if he used the File Exchange file. Justin, any reason why you're not using the built-in "makecform()" function?