problems converting to 8-bit image

[Name Suppressed - 000002948]

I have quite a few images of plant roots traced in blue and black
marker. I'm trying to do some fractal analysis and want to convert
these images to 8-bit grayscale. The images are currently 8-bit color.
I've tried using 'image->type->8-bit' and that works for some of my
images, but for others the entire image becomes black. I tried
thresholding first and that will convert the entire root system to
black, but when I try converting to 8-bit grayscale the entire image
still becomes black.  Is there anything I can do about this?

Thanks,
Kathryn Barto
Environmental Science PhD Program
Wright State University

[Robert Baer]

You could try converting to RGB color first, and then to RGB grayscale or
alternaively then using using Image<Color<RGB Split to create three separate
grayscale images one of which should give you the best contrast.

Rob Baer

____________________________
Robert W. Baer, Ph.D.
Associate Professor
Department of Physiology
A. T. Still University of Health Science
800 W. Jefferson St.
Kirksville, MO 63501-1497 USA
----- Original Message -----
From: "Name Suppressed - 000002948" <[hidden email]>
To: <[hidden email]>
Sent: Friday, April 07, 2006 2:29 PM
Subject: problems converting to 8-bit image

> I have quite a few images of plant roots traced in blue and black
> marker. I'm trying to do some fractal analysis and want to convert
> these images to 8-bit grayscale. The images are currently 8-bit color.
> I've tried using 'image->type->8-bit' and that works for some of my
> images, but for others the entire image becomes black. I tried
> thresholding first and that will convert the entire root system to
> black, but when I try converting to 8-bit grayscale the entire image
> still becomes black.  Is there anything I can do about this?
>
> Thanks,
> Kathryn Barto
> Environmental Science PhD Program
> Wright State University
>

[Gabriel Landini]

On Friday 07 April 2006 20:29, Name Suppressed - 000002948 wrote:
> I have quite a few images of plant roots traced in blue and black
> marker. I'm trying to do some fractal analysis and want to convert
> these images to 8-bit grayscale. The images are currently 8-bit color.
> I've tried using 'image->type->8-bit' and that works for some of my
> images, but for others the entire image becomes black. I tried
> thresholding first and that will convert the entire root system to
> black, but when I try converting to 8-bit grayscale the entire image
> still becomes black.  Is there anything I can do about this?

The 8 bit colour images have a palette, that is why one cannot threshold
properly (the palette is not likely to be in brightness order).
You can try to convert them to RGB first, and then to 8 bit grey.
The colours in the RGB image will remain quantised, but converting to 8 bit
grey may still be enough to be able to threshold them.
Once in RGB mode you can also try the colour_threshold plugin at my site.
Cheers,

G.

[Name Suppressed - 000002948]

Converting to RGB first took care of it.

Thanks,
Kathryn Barto


Gabriel Landini wrote:

>On Friday 07 April 2006 20:29, Name Suppressed - 000002948 wrote:
>> I have quite a few images of plant roots traced in blue and black
>> marker. I'm trying to do some fractal analysis and want to convert
>> these images to 8-bit grayscale. The images are currently 8-bit color.
>> I've tried using 'image->type->8-bit' and that works for some of my
>> images, but for others the entire image becomes black. I tried
>> thresholding first and that will convert the entire root system to
>> black, but when I try converting to 8-bit grayscale the entire image
>> still becomes black.  Is there anything I can do about this?
>
>The 8 bit colour images have a palette, that is why one cannot

threshold
>properly (the palette is not likely to be in brightness order).
>You can try to convert them to RGB first, and then to 8 bit grey.
>The colours in the RGB image will remain quantised, but converting to 8
bit
>grey may still be enough to be able to threshold them.
>Once in RGB mode you can also try the colour_threshold plugin at my
site.
>Cheers,
>
>G.
>