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Re: color_quan - how for exactly 256 colors? [message #36802 is a reply to message #36755]

Fri, 24 October 2003 08:34

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

Ok, I'm confused.

JD Smith wrote the other day in response to Mr. Thilmann:

>> What I mean is: I know that my image contains not more than 256
>> different RGB colors (out of 16.7 million) - I created the RGB image
>> from an indexed image and now I want to transform it back. This can be
>> done exactly and I wondered whether IDL provides a method to get that
>> done. Cheers,
>
> Yes, with HISTOGRAM:
>
> rgb_image=r+256L*(g+256L*b)
> h=histogram(rgb_image,OMIN=om)
> wh=where(h gt 0,cnt) # Should be fewer than 256
> h[wh]=bindgen(cnt)
> index_image=h[rgb_image-om]
> colors=om+wh ; these are your <=256 colors
> r_vec=colors AND 255L
> g_vec=ishft(colors,-8) AND 255L
> b_vec=ishft(colors,-16) AND 255L
> tvlct,r_vec,g_vec,b_vec
> tv,index_image
>
> Probably not the most efficient method in the universe, given the
> sparseness of the histogram, but it gets the job done.

To which Oliver responded with this:

> Impressive :)
> Works like a charm. Thank you!

But,... it's not working like a charm for me. :-(

In fact, when I run this code, I find that index_image
is a LONG *vector*, not the 2D image I was expecting.
What am I missing here?

In line three:

wh=where(h gt 0,cnt) # Should be fewer than 256

I used:

wh=where(h gt 0,cnt) # 255

How does this "work like a charm"?

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		color_quan - how for exactly 256 colors? By: justspam03 on Thu, 16 October 2003 08:39
		Re: color_quan - how for exactly 256 colors? By: justspam03 on Sun, 19 October 2003 06:29
		Re: color_quan - how for exactly 256 colors? By: JD Smith on Fri, 17 October 2003 14:35
		Re: color_quan - how for exactly 256 colors? By: David Fanning on Fri, 17 October 2003 12:57
		Re: color_quan - how for exactly 256 colors? By: JD Smith on Fri, 17 October 2003 11:57
		Re: color_quan - how for exactly 256 colors? By: David Fanning on Fri, 24 October 2003 08:34
		Re: color_quan - how for exactly 256 colors? By: David Fanning on Fri, 24 October 2003 09:17
		Re: color_quan - how for exactly 256 colors? By: JD Smith on Fri, 24 October 2003 08:55

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