Re: Imwrite with colormap

On 10/19/2012 5:25 AM, Nicolás wrote:
> Good morning.
> I am trying to use imwrite to save a image with a colormap( for example,
> 'jet'), and with a value of 25 levels, such as this:
> imwrite(handles.image,handles.colorMap,filename,pathname);
>
> However, the image is not saved with the value of levels established
> previously. Thus the image is saved with a value of 256 leves, instead
> of 25.
>
> Anyone knows do it?
> Thanks in advance.

The same question came in from a MathWorks training engineer this week.

You didn't say what file format you are using, but I'll assume you are
writing a TIFF file.

In the TIFF file format spec, it says that the number of colors in the
colormap is 2^n, where n is the number of bits per sample. (For
details, see section 5, "Palette-color images," of the TIFF spec.
http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf)

So it is not possible to make a TIFF file that has a colormap with only
25 colors in it.

--
Steve Eddins
http://blogs.mathworks.com/steve/