Re: problems converting to 8-bit image

Posted by Gabriel Landini on Apr 08, 2006; 9:07am
URL: http://imagej.273.s1.nabble.com/problems-converting-to-8-bit-image-tp3703137p3703139.html

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.