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diff --git a/man/man7/color.html b/man/man7/color.html deleted file mode 100644 index 262e4633..00000000 --- a/man/man7/color.html +++ /dev/null @@ -1,169 +0,0 @@ -<head> -<title>color(7) - Plan 9 from User Space</title> -<meta content="text/html; charset=utf-8" http-equiv=Content-Type> -</head> -<body bgcolor=#ffffff> -<table border=0 cellpadding=0 cellspacing=0 width=100%> -<tr height=10><td> -<tr><td width=20><td> -<tr><td width=20><td><b>COLOR(7)</b><td align=right><b>COLOR(7)</b> -<tr><td width=20><td colspan=2> - <br> -<p><font size=+1><b>NAME </b></font><br> - -<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> - - color – representation of pixels and colors<br> - -</table> -<p><font size=+1><b>DESCRIPTION </b></font><br> - -<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> - - To address problems of consistency and portability among applications, - Plan 9 uses a fixed color map, called <tt><font size=+1>rgbv</font></tt>, on 8-bit-per-pixel - displays. Although this avoids problems caused by multiplexing - color maps between applications, it requires that the color map - chosen be suitable for most purposes and usable for - all. Other systems that use fixed color maps tend to sample the - color cube uniformly, which has advantages--mapping from a (red, - green, blue) triple to the color map and back again is easy--but - ignores an important property of the human visual system: eyes - are much more sensitive to small changes in intensity than - to changes in hue. Sampling the color cube uniformly gives a color - map with many different hues, but only a few shades of each. Continuous - tone images converted into such maps demonstrate conspicuous artifacts. - - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - Rather than dice the color cube into subregions of size 6×6×6 (as - in Netscape Navigator) or 8×8×4 (as in previous releases of Plan - 9), picking 1 color in each, the <tt><font size=+1>rgbv</font></tt> color map uses a 4×4×4 subdivision, - with 4 shades in each subcube. The idea is to reduce the color - resolution by dicing the color cube into fewer - cells, and to use the extra space to increase the intensity resolution. - This results in 16 grey shades (4 grey subcubes with 4 samples - in each), 13 shades of each primary and secondary color (3 subcubes - with 4 samples plus black) and a reasonable selection of colors - covering the rest of the color cube. The advantage is - better representation of continuous tones. - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - The following function computes the 256 3-byte entries in the - color map:<br> - - <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> - - <tt><font size=+1>void<br> - setmaprgbv(uchar cmap[256][3])<br> - {<br> - - <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> - - uchar *c;<br> - int r, g, b, v;<br> - int num, den;<br> - int i, j;<br> - for(r=0,i=0; r!=4; r++)<br> - for(v=0; v!=4; v++,i+=16)<br> - for(g=0,j=v−r; g!=4; g++)<br> - for(b=0; b!=4; b++,j++){<br> - c = cmap[i+(j&15)];<br> - den = r;<br> - if(g > den)<br> - den = g;<br> - if(b > den)<br> - den = b;<br> - if(den == 0) /* would divide check; pick grey shades */<br> - c[0] = c[1] = c[2] = 17*v;<br> - else{<br> - num = 17*(4*den+v);<br> - c[0] = r*num/den;<br> - c[1] = g*num/den;<br> - c[2] = b*num/den;<br> - }<br> - }<br> - - </table> - }<br> - - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - </font></tt> - - </table> - There are 4 nested loops to pick the (red,green,blue) coordinates - of the subcube, and the value (intensity) within the subcube, - indexed by <tt><font size=+1>r</font></tt>, <tt><font size=+1>g</font></tt>, <tt><font size=+1>b</font></tt>, and <tt><font size=+1>v</font></tt>, whence the name <i>rgbv</i>. The peculiar - order in which the color map is indexed is designed to distribute - the grey shades uniformly through the map--the <i>i</i>’th grey - shade, 0<=<i>i</i><=15 has index <i>i</i>x17, with black going to 0 and white to - 255. Therefore, when a call to <tt><font size=+1>draw</font></tt> converts a 1, 2 or 4 bit-per-pixel - picture to 8 bits per pixel (which it does by replicating the - pixels’ bits), the converted pixel values are the appropriate - grey shades. - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - The <tt><font size=+1>rgbv</font></tt> map is not gamma-corrected, for two reasons. First, photographic - film and television are both normally under-corrected, the former - by an accident of physics and the latter by NTSC’s design. Second, - we require extra color resolution at low intensities because of - the non-linear response and adaptation of - the human visual system. Properly gamma-corrected displays with - adequate low-intensity resolution pack the high-intensity parts - of the color cube with colors whose differences are almost imperceptible. - Either reason suggests concentrating the available intensities - at the low end of the range. - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - On ‘true-color’ displays with separate values for the red, green, - and blue components of a pixel, the values are chosen so 0 represents - no intensity (black) and the maximum value (255 for an 8-bit-per-color - display) represents full intensity (e.g., full red). Common display - depths are 24 bits per pixel, with 8 bits per - color in order red, green, blue, and 16 bits per pixel, with 5 - bits of red, 6 bits of green, and 5 bits of blue. - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - Colors may also be created with an opacity factor called <tt><font size=+1>alpha</font></tt>, - which is scaled so 0 represents fully transparent and 255 represents - opaque color. The alpha is <i>premultiplied</i> into the other channels, - as described in the paper by Porter and Duff cited in <a href="../man3/draw.html"><i>draw</i>(3)</a>. - The function <tt><font size=+1>setalpha</font></tt> (see <a href="../man3/allocimage.html"><i>allocimage</i>(3)</a>) aids the - initialization of color values with non-trivial alpha. - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - The packing of pixels into bytes and words is odd. For compatibility - with VGA frame buffers, the bits within a pixel byte are in big-endian - order (leftmost pixel is most significant bits in byte), while - bytes within a pixel are packed in little-endian order. Pixels - are stored in contiguous bytes. This results in unintuitive - pixel formats. For example, for the RGB24 format, the byte ordering - is blue, green, red. - <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> - - To maintain a constant external representation, the <a href="../man3/draw.html"><i>draw</i>(3)</a> interface - as well as the various graphics libraries represent colors by - 32-bit numbers, as described in <a href="../man3/color.html"><i>color</i>(3)</a>.<br> - -</table> -<p><font size=+1><b>SEE ALSO </b></font><br> - -<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> - - <a href="../man3/color.html"><i>color</i>(3)</a>, <a href="../man3/graphics.html"><i>graphics</i>(3)</a>, <a href="../man3/draw.html"><i>draw</i>(3)</a><br> - -</table> - -<td width=20> -<tr height=20><td> -</table> -<!-- TRAILER --> -<table border=0 cellpadding=0 cellspacing=0 width=100%> -<tr height=15><td width=10><td><td width=10> -<tr><td><td> -<center> -<a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a> -</center> -</table> -<!-- TRAILER --> -</body></html> |