Imwrite with colormap

[Nicolás]

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.

[Steve Eddins]

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/

[Nicolás]

"Steve Eddins" wrote in message <k5rf8i$nuh$1...@newscl01ah.mathworks.com>...

Sorry, but the file format can be jpeg,jpeg 2000,gif,etc,etc, in summary those supported by Matlab.
And another thing. I don't want to save the level of color. What I want to save is the level of intensitiy. When you have a image, you have from 0 to 255 levels of intensity. I want to modify the colormap of the image and then, modifying the level of intensity.

I hope now it is more clear the question.

Thanks you a lot !

[Steve Eddins]

JPEG files can't store indexed images.

If you want to store the intensity values directly, then don't write an
indexed image with a colormap. For example, write a TIFF file this way:

imwrite(A,'myfilename.tif')

[Nicolás]

"Steve Eddins" wrote in message <k5rs4e$fj5$1...@newscl01ah.mathworks.com>...

Oh my god! You're completely right! I have confirmed this information and it's true.
I have wasted some hours to do an impossible thing. :(

Thanks a lot!