Math Forum Discussions

Nicolás

Posts: 10
Registered: 10/18/12

Re: Imwrite with colormap
Posted: Oct 19, 2012 12:29 PM

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"Steve Eddins" wrote in message <k5rs4e$fj5$1@newscl01ah.mathworks.com>...
> On 10/19/2012 11:08 AM, Nicolás wrote:
> > "Steve Eddins" wrote in message <k5rf8i$nuh$1@newscl01ah.mathworks.com>...
> >> 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/
> >
> >
> > 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 !
>
> 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')
>
> --
> Steve Eddins
> http://blogs.mathworks.com/steve/

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!