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From: ellswort@sargent.cs.unc.edu (David Ellsworth)
Newsgroups: comp.graphics
Subject: Re: bug in hls_to_rgb from Foley, van Dam, Feiner, Hughes
Message-ID: <16453@thorin.cs.unc.edu>
Date: 2 Oct 90 00:49:52 GMT
References: <9009301931.AA14664@nth.com>
Sender: news@thorin.cs.unc.edu
Reply-To: ellswort@sargent.cs.unc.edu (David Ellsworth)
Organization: University Of North Carolina, Chapel Hill
Lines: 30

In article <9009301931.AA14664@nth.com> andy@nthropy.UUCP (Andy Lowe) writes:
>
>I had occasion to implement an hls to rgb converter for a research 
>project, and turned to the new Foley, vanDam, Feiner, Hughes book for
>the algorithm.
>
>On p. 596 is a procedure that purports to do the conversion.  While
>studying it, I couldn't see how it worked. (various problems omitted)
>
>Can someone tell me I'm wrong? (please.)
>
> (pseudocode on how the algorithm is wrong deleted)

Sorry, you are right.  The bug list for the book lists these problems
with the figure you are referencing:

596, Fig. 13.37, line 4:  "n1, n2, hue" -> "n1, n2, hue: real"
596, Fig. 13.37, line 8:  "if" -> "else if"
596, Fig. 13.37, line 10:  ">" -> "<"
596, Fig. 13.37, line 15:  "n2 - 1" -> "n2 - n1"
596, Fig. 13.37, line 22: "l + s - l * s" -> "l + s + l * s"
596, Fig. 13.37, line 23:  move line left, flush with "else" two lines above

I got the bug list by sending a message to graphtext@cs.brown.edu with a
subject of "Get-Text-Bug-List" (as described in a posting about 80 articles
back by ethan@thinc.UUCP (Ethan Lish)).

---------------
David Ellsworth
ellswort@cs.unc.edu