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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.2 Final//FR"><!-- Converted with LaTeX2HTML 95.1 (Fri Jan 20 1995) --><!-- by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --><!-- Modified Simulog 03/97 --><HTML><HEAD><TITLE>5.1 Color</TITLE><LINK REL=STYLESHEET TYPE="text/css" HREF="./Modulef.css" TITLE="Modulef CSS"><meta name="description" value="5.1 Color"><meta name="keywords" value="Guide6"><meta name="resource-type" value="document"><meta name="distribution" value="global"></HEAD><BODY BGCOLOR="#FFFFFF"><P> <IMG SRC="../icons/smallmod.gif" WIDTH=211 HEIGHT=50 ALIGN=BOTTOM ALT="Modulef"><A NAME=tex2html1481 HREF="node85.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/previous_motif.gif" ALT="previous"></A><A NAME=tex2html1487 HREF="node85.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/up_motif.gif" ALT="up"></A><A NAME=tex2html1489 HREF="node87.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/next_motif.gif" ALT="next"></A><A NAME=tex2html1491 HREF="node2.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/contents_motif.gif" ALT="contents"></A><A HREF="../Guide6-18/node86.html"><IMG BORDER=0 SRC="../icons/zoom18.gif" ALIGN=BOTTOM ALT="[BIG]"></A><A HREF="../Guide6-14/node86.html"><IMG BORDER=0 SRC="../icons/zoom14.gif" ALIGN=BOTTOM ALT="[Normal]"></A><A HREF="../Guide6-10/node86.html"><IMG BORDER=0 SRC="../icons/zoom10.gif" ALIGN=BOTTOM ALT="[small]"></A><BR><B> Next: </B> <A NAME=tex2html1490 HREF="node87.html">5.2 Stereoscopy</A><B>Up: </B> <A NAME=tex2html1488 HREF="node85.html">5 Graphics</A><B> Prev: </B> <A NAME=tex2html1482 HREF="node85.html">5 Graphics</A><B><A HREF="node2.html" >Contents</A></B><HR SIZE=3 WIDTH="75%"><H1><A NAME=SECTION05510000000000000000>5.1 Color</A></H1><P><P><P>We will now see how to construct a color<A NAME=3251> </A> on a terminal which permits it.<P>In the preceding subroutines, the colors were designated by integer numbers.0 corresponds to the background color. For a terminal with N colors, the numbers lyingbetween 1 and N-1 correspond to the different colors in the terminal's color table.This color table is, in general, initialized after the output terminal is selected.It is however possible to modify it of to set a color equal to the current color.<P><P><P>Let us first recall some preliminary notions regarding colors.<P>On a color terminal with a cathodic-ray tube, the different colors are obtained by the combinationof the three basic colors: RED, GREEN and BLUE (RGB).<P><PRE> RED + GREEN = YELLOW RED + BLUE = MAGENTA GREEN + BLUE = CYAN RED + GREEN + BLUE = WHITE</PRE><P>The intermediary colors are obtained by putting a multiplicative factor, between 0. and 1., with each of the basic colors. So, let X, Y and Z be 3 numbers between 0. and 1., then we can obtain all the possible colorsand vary them by using the following equation:<P> <DIV ALIGN=center><IMG BORDER=0 ALIGN=MIDDLE ALT="" SRC="img135.gif"></DIV><P>We call the colors additive, as they are obtained by adding the basic colors.<P><P><A NAME=3588> </A><IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img136.gif"><BR><STRONG>Figure 5.1:</STRONG> <i> RGB coordinate system</i><A NAME=3584iRGBcoordinatesystemi3584> </A><BR><P><P>The above is no longer true for a printer type color terminal. The basic colorsare the following: MAGENTA, YELLOW and CYAN. The colors are no longer additive, but subtractive:<P><PRE> MAGENTA + YELLOW = RED MAGENTA + CYAN = BLUE YELLOW + CYAN = GREEN MAGENTA + YELLOW + CYAN = BLACK</PRE><P> Here too, by combining the three basic colors linearly, all the colors can be obtained.<P><P><P> FORTRAN 3D functions with the RGB system.<P><P><P>In certain applications, it can be desirable to work in cylindrical coordinates.We change therefore to the "HSV" (Hue, Saturation and Value) coordinate system.<P><UL><LI> H (Hue) varies from 0 to 1 and describes the different hues:<P><UL><LI> 0 RED <LI> 1/6 YELLOW <LI> 2/6 GREEN <LI> 3/6 CYAN <LI> 4/6 BLUE <LI> 5/6 MAGENTA <LI> 1 RED</UL><P><LI> S (Saturation) varies form 0 to 1 and determines the color's saturation level:<UL><LI> close to 0, we tend to gray (or white); <LI> close to 1, we tend to a pure color.</UL><P><LI> V (Intensity) varies from 0 to 1 and determines the intensity:<UL><LI> 0 black <LI> 1 white</UL></UL><P><P><A NAME=3598> </A><IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img137.gif"><BR><STRONG>Figure 5.2:</STRONG> <i> Two possible representations of the HSV coordinate system</i><A NAME=3594iTwopossiblerepresentationsoftheHSVcoordinatesystemi3594> </A><BR><P><P><UL><LI><P><PRE> SUBROUTINE HSVRGB(H, S, V, R, G, B) REAL H, S, V, R, G, B</PRE><P>converts a color described in HSV (H, S, V) into <A NAME=3267> </A> RGB (R, G, B).<P> <LI><P><PRE> SUBROUTINE RGBHSV(R, G, B, H, S, V) REAL H, S, V, R, G, B</PRE><P>converts a color described in RGB (R, G, B) into <A NAME=3268> </A> HSV (H, S, V).<P><LI><P><PRE> SUBROUTINE SETCOL(R, V, B) REAL R, V, B</PRE><P>Variables <A NAME=3269> </A> R, G and B lie between 0. and 1., and play the same role as X, Y and Z above (figure <A HREF="#figRVB">5.1</A>).This subroutine sets R, G and B equal to the current color.<P><LI><P><PRE> SUBROUTINE SETTBC(R, G, B, I1, I2, IRET) INTEGER I1, I2, IRET REAL R(I2-I1+1), G(I2-I1+1), B(I2-I1+1)</PRE><P>restricts, in the <A NAME=3271> </A>color table<A NAME=3272> </A>, R, G and B to lie between indices I1 and I2 inclusively (the three arrays contain the numbers lying between 0 and 1).If the color table can be modified, IRET = 0, of not IRET <IMG BORDER=0 ALIGN=MIDDLE ALT="" SRC="img118.gif"> 0.The index 0 corresponds to a background color.<P> </UL><P> <P><P> <HR SIZE=3 WIDTH="75%"><IMG SRC="../icons/smallmod.gif" WIDTH=211 HEIGHT=50 ALIGN=BOTTOM ALT="Modulef"><A NAME=tex2html1481 HREF="node85.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/previous_motif.gif" ALT="previous"></A><A NAME=tex2html1487 HREF="node85.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/up_motif.gif" ALT="up"></A><A NAME=tex2html1489 HREF="node87.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/next_motif.gif" ALT="next"></A><A NAME=tex2html1491 HREF="node2.html"><IMG BORDER=0 ALIGN=BOTTOM SRC="../icons/contents_motif.gif" ALT="contents"></A><A HREF="../Guide6-18/node86.html"><IMG BORDER=0 SRC="../icons/zoom18.gif" ALIGN=BOTTOM ALT="[BIG]"></A><A HREF="../Guide6-14/node86.html"><IMG BORDER=0 SRC="../icons/zoom14.gif" ALIGN=BOTTOM ALT="[Normal]"></A><A HREF="../Guide6-10/node86.html"><IMG BORDER=0 SRC="../icons/zoom10.gif" ALIGN=BOTTOM ALT="[small]"></A><BR><B> Next: </B> <A NAME=tex2html1490 HREF="node87.html">5.2 Stereoscopy</A><B>Up: </B> <A NAME=tex2html1488 HREF="node85.html">5 Graphics</A><B> Prev: </B> <A NAME=tex2html1482 HREF="node85.html">5 Graphics</A><B><A HREF="node2.html" >Contents</A></B><BR> <HR><P><ADDRESS></ADDRESS></BODY></HTML>⌨️ 快捷键说明
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