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diff --git a/doc/developer/reference-html/c1968.html b/doc/developer/reference-html/c1968.html new file mode 100644 index 0000000..e03ce26 --- /dev/null +++ b/doc/developer/reference-html/c1968.html @@ -0,0 +1,953 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> +<HTML +><HEAD +><TITLE +>Dithering</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK +REL="HOME" +TITLE="The Developer's Guide to Gutenprint" +HREF="index.html"><LINK +REL="PREVIOUS" +TITLE="Weaving algorithms" +HREF="x1734.html"><LINK +REL="NEXT" +TITLE="GNU General Public License" +HREF="a2122.html"></HEAD +><BODY +CLASS="chapter" +BGCOLOR="#FFFFFF" +TEXT="#000000" +LINK="#0000FF" +VLINK="#840084" +ALINK="#0000FF" +><DIV +CLASS="NAVHEADER" +><TABLE +SUMMARY="Header navigation table" +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>The Developer's Guide to Gutenprint</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="x1734.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +></TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="a2122.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="chapter" +><H1 +><A +NAME="AEN1968" +></A +>Chapter 7. Dithering</H1 +><P +> The dithering code in + <TT +CLASS="filename" +>src/main/print-dither.c</TT +> attempts to + reproduce various shades of gray (or all colors) from only a few + different inks (black, cyan, magenta, yellow, and sometimes + light cyan and light magenta). The dots can't vary in darkness + or size (except for certain special printers), and so we need to + lay down a certain fraction of dots to represent each distinct + level. + </P +><P +> This sounds straightforward; in practice, it isn't. Completely + random distribution of dots (simple probabilistic dithering) + would create grainy clumps and light spots. The smoothest + pattern results from an equidistant spacing of dots. + Approximating this requires sophisticated algorithms. We have + two dithering algorithms, an ordered dither algorithm that uses + a grid (matrix) to decide whether to print, and a modified + Floyd-Steinberg error diffusion algorithm that uses a grid in a + slightly different way. + </P +><P +> We currently have three dithering functions: + </P +><P +></P +><DIV +CLASS="variablelist" +><DL +><DT +><TT +CLASS="literal" +>dither_fastblack</TT +></DT +><DD +><P +> This produces pure black or white from a pre-dithered + input. This is used for two purposes: for printing pure + black and white very quickly (e.g. text), and for printing + pre-screened monochrome output that was rasterized + externally. + </P +></DD +><DT +><TT +CLASS="literal" +>dither_black</TT +></DT +><DD +><P +> This produces black from grayscale input. The new + dither_black can produce either a single or multiple + levels of black, for printers supporting variable dot + size. + </P +></DD +><DT +><TT +CLASS="literal" +>dither_cmyk</TT +></DT +><DD +><P +> This produces 3, 4, 5, 6, or 7 color output (CMY, CMYK, + CcMmYK, CcMmYy, CcMmYyK, or any variants). The new + routine can handle single or multiple levels of each + color. + </P +></DD +></DL +></DIV +><P +> There is a choice of dithering algorithms. Four of them are + based on a basic error diffusion, with a few tweaks of my own. + The other one is ‘ordered’. However, they all share + the basic operation in common. First, the algorithm picks what + kind of dot (if there are multiple dot sizes and/or tones that + may be picked) is the candidate to be printed. This decision is + made based on the darkness at the point being dithered. Then, + it decides whether the dot will be printed at all. What this is + based on depends upon which algorithm family we use. This is + all described in more detail below. + </P +><P +> Ordered dithering works by comparing the value at a given point + with the value of a tiled matrix. If the value at the point is + greater than the value in the matrix, the dot is printed. The + matrix should consist of a set of evenly spaced points between 0 + and the upper limit. The choice of matrix is very important for + print quality. A good dither matrix will emphasize high + frequency components, which distributes dots evenly with a + minimum of clumping. The matrices used here are all simple + matrices that are expanded recursively to create larger matrices + with the same kind of even point distribution. This is + described below. + </P +><P +> Note that it is important to use different matrices for the two + sub-operations, because otherwise the choice about whether to + print and the choice of dot size will be correlated. The usual + result is that the print is either too dark or too light, but + there can be other problems. + </P +><P +> Ordered dithering works quite well on single dot size, four + color printers. It has not been well tested on four color, + variable dot size printers. It should be avoided on six color + printers. + </P +><P +> Error diffusion works by taking the output error at a given + pixel and “diffusing” it into surrounding pixels. + Output error is the difference between the amount of ink output + and the input level at each pixel. For simple printers, with + one or four ink colors and only one dot size, the amount of ink + output is either 65536 (i. e. full output) or 0 (no output). + The difference between this and the input level is the error. + Normal error diffusion adds part of this error to the adjoining + pixels in the next column and the next row (the algorithm simply + scans each row in turn, never backing up). The error adds up + until it reaches a threshold (half of the full output level, or + 32768), at which point a dot is output, the output is subtracted + from the current value, and the (now negative) error is diffused + similarly. + </P +><P +> Error diffusion works quite well in general, but it tends to + generate artifacts which usually appear as worm-like lines or + areas of anomalous density. I have devised some ways, as + described below, of ameliorating these artifacts. + </P +><P +> There are two sub-classes of error diffusion that we use here, + ‘random’ and ‘hybrid’. One of the + techniques that we use to ameliorate the artifacts is to use a + fuzzy threshold rather than the hard threshold of half of the + output level. Random error diffusion uses a pseudo-random + number to perturb the threshold, while hybrid error diffusion + uses a matrix. Hybrid error diffusion worked very poorly in + 3.1.3, and I couldn't figure out why until I found a bug. It + now works very well. + </P +><P +> There is one additional variant (on both sub-classes), called + ‘adaptive hybrid’ and ‘adaptive random’. + The adaptive variant takes advantage of the fact that the + patterns that ordered dithering create are less visible at very + low densities, while the artifacts created by error diffusion + are more objectionable at low densities. At low densities, + therefore, it uses ordered dithering; at higher densities it + uses error diffusion. + </P +><P +> Handling multiple output levels makes life a bit more + complicated. In principle, it shouldn't be much harder: simply + figure out what the ratio between the available output levels is + and have multiple thresholds. In practice, getting these right + involves a lot of trial and error. The other thing that's + important is to maximize the number of dots that have some ink. + This will reduce the amount of speckling. More on this later. + </P +><P +> The next question: how do we handle black when printing in + color? Black ink is much darker than colored inks. It's + possible to produce black by adding some mixture of cyan, + magenta, and yellow—in principle. In practice, the black + really isn't very black, and different inks and different papers + will produce different color casts. However, by using CMY to + produce gray, we can output a lot more dots! This makes for a + much smoother image. What's more, one cyan, one magenta, and + one yellow dot produce less darkness than one black dot, so + we're outputting that many more dots. Better yet, with 6 or 7 + color printers, we have to output even more light ink dots. So + Epson Stylus Photo printers can produce really smooth grays---if + we do everything right. The right idea is to use CMY at lower + black levels, and gradually mix in black as the overall amount + of ink increases, so the black dots don't really become visible + within the ink mass. + </P +><P +> Variable dot sizes are handled by dividing the range between 0 + and 65536 into segments. Each segment can either represent a + range in which all of one kind of ink (color and/or dot size) is + used, with varying amounts of ink, or a transition region + between inks, in which equal numbers of dots are printed but the + amount of each ink will be adjusted throughout the range. Each + range is represented by four numbers: + </P +><P +></P +><UL +><LI +><P +> Bottom of the range. + </P +></LI +><LI +><P +> Top of the range. + </P +></LI +><LI +><P +> Value of the lighter ink. + </P +></LI +><LI +><P +>Value of the darker ink. + </P +></LI +></UL +><P +> In addition, the bit patterns and which type of ink are also + represented, but they don't affect the actual algorithm. + </P +><P +> As mentioned above, the basic algorithm is the same whether we + use ordered dither or error diffusion. We perform the following + steps on each color of each pixel: + </P +><P +></P +><OL +TYPE="1" +><LI +><P +> Compute the value of the particular color we're printing. + This isn't usually the pure CMY value; it's adjusted to + improve saturation and to limit the use of black in light + toned regions (to avoid speckling). + </P +></LI +><LI +><P +> Find the range containing this value. + </P +></LI +><LI +><P +> Compute where this value lies within the range. We scale + the endpoints between 0 and 65536 for this purpose. So for + example, if the bottom of the range is 10,000 and the top of + the range is 20,000, and the value is 12,500, we're 1/4 of + the way between the bottom and the top of the range, so our + scale point is 16384. + </P +></LI +><LI +><P +> Compute the “virtual value”. The virtual value + is the distance between the value of the lighter and the + value of the darker ink. So if the value of the light ink + is 32768 and the dark ink is 65536, we compute a virtual + value scaled appropriately between these two values, which + is 40960 in this case. + </P +></LI +><LI +><P +> Using either error diffusion or ordered dither, the standard + threshold is 1/2 of the value (20480 in this case). Using + ordered dither, we want to compute a value between 0 and + 40960 that we will compare the input value against to decide + whether to print. Using pure error diffusion, we would + compare the accumulated error against 20480 to decide + whether to print. In practice, we use the same matrix + method to decide whether to print. The correct amount of + ink will be printed this way, but we minimize the squiggly + lines characteristic of error diffusion by dithering the + threshold in this fashion. A future enhancement will allow + us to control the amount of dithering applied to the + threshold. + </P +></LI +></OL +><P +> The matrices were generated by Thomas Tonino + <CODE +CLASS="email" +><<A +HREF="mailto:ttonino@bio.vu.nl" +>ttonino@bio.vu.nl</A +>></CODE +> with an algorithm of his + devising. The algorithm is designed to maximize the spacing + between dots at any given density by searching the matrix for + holes and placing a dot in the largest available hole. It + requires careful selection of initial points to achieve good + results, and is very time consuming. For best results, a + different matrix must be used for modes with 2:1 aspect ratio + (e.g. 1440×720) than for 1:1 (e. g. 720×720). It is + essential with any of these matrices that every point be used. + Skipping points generates low-frequency noise. + </P +><P +> It's essential to use different matrices for deciding whether to + print and for deciding what color (dark or light) to print. + This should be obvious; the decision about whether to print at + all should be as independent as possible from the decision about + what color to print, because any bias will result in excess + light or dark ink being printed, shifting the tonal balance. We + actually use the same matrices, but we shift them vertically and + horizontally. Assuming that the matrices are not + self-correlated, this will yield good results. + </P +><P +> The ranges are computed from a list of ink values (between 0 and + 1 for each possible combination of dot size and ink tone, where + the value represents the darkness of the ink) and the desired + maximum density of the ink. This is done in dither_set_ranges, + and needs more documentation. + </P +><P +> I stated earlier that I've tweaked the basic error diffusion + algorithm. Here's what I've done to improve it: + </P +><P +></P +><UL +><LI +><P +> We use a variable threshold to decide when to print, as + discussed above. This does two things for us: it reduces + the slightly squiggly diagonal lines that are the mark of + error diffusion; and it allows us to lay down some ink even + in very light areas near the edge of the image. The + squiggly lines that error diffusion algorithms tend to + generate are caused by the gradual accumulation of error. + This error is partially added horizontally and partially + vertically. The horizontal accumulation results in a dot + eventually being printed. The vertical accumulation results + in a dot getting laid down in roughly the same horizontal + position in the next row. The diagonal squigglies result + from the error being added to pixels one forward and one + below the current pixel; these lines slope from the top + right to the bottom left of the image. + </P +><P +> Error diffusion also results in pale areas being completely + white near the top left of the image (the origin of the + printing coordinates). This is because enough error has to + accumulate for anything at all to get printed. In very pale + areas it takes quite a long time to build up anything + printable at all; this results in the bare spots. + </P +><P +> Randomizing the threshold somewhat breaks up the diagonals + to some degree by randomizing the exact location that the + accumulated output crosses the threshold. It reduces the + false white areas by allowing some dots to be printed even + when the accumulated output level is very low. It doesn't + result in excess ink because the full output level is still + subtracted and diffused. + </P +><P +> Excessive randomization leads to blobs at high densities. + Therefore, as the density increases, the degree of + randomization decreases. + </P +></LI +><LI +><P +> Alternating scan direction between rows (first row is + scanned left to right, second is scanned right to left, and + so on). This also helps break up white areas, and it also + seems to break up squigglies a bit. Furthermore, it + eliminates directional biases in the horizontal direction. + This isn't necessary for ordered dither, but it doesn't hurt + either. + </P +></LI +><LI +><P +> Diffusing the error into more pixels. Instead of diffusing + the entire error into (X+1, Y) and (X, Y+1), we diffuse it + into (X+1, Y), (X+K, Y+1), (X, Y+1), (X-K, Y+1) where K + depends upon the output level (it never exceeds about 10 + dots, and is greater at higher output levels). This really + reduces squigglies and graininess. The amount of this + spread can be controlled; for line art, it should be less + than for photographs (of course, line art doesn't usually + contain much light color, but the <SPAN +CLASS="emphasis" +><I +CLASS="emphasis" +>error</I +></SPAN +> + value can be small in places!) In addition to requiring + more computation, a wide ink spread results in patterning at + high dot densities (note that the dot density can be high + even in fairly pale regions if multiple dot sizes are in + use). + </P +></LI +><LI +><P +> Don't lay down any colored ink if we're laying down black + ink. There's no point; the colored ink won't show. We + still pretend that we did for purposes of error diffusion + (otherwise excessive error will build up, and will take a + long time to clear, resulting in heavy bleeding of ink into + surrounding areas, which is very ugly indeed), but we don't + bother wasting the ink. How well this will do with variable + dot size remains to be seen. + </P +></LI +><LI +><P +> Oversampling. This is how to print 1440×720 with Epson + Stylus printers. Printing full density at 1440×720 will + result in excess ink being laid down. The trick is to print + only every other dot. We still compute the error as though we + printed every dot. It turns out that randomizing which dots + are printed results in very speckled output. This can be + taken too far; oversampling at 1440×1440 or + 1440×2880 virtual resolution results in other problems. + However, at present 1440×1440 (which is more accurately + called "1440×720 enhanced", as the Epson printers cannot + print 1440 rows per inch) does quite well, although it's slow. + </P +></LI +></UL +><P +> What about multiple output levels? For 6 and 7 color printers, + simply using different threshold levels has a problem: the pale + inks have trouble being seen when a lot of darker ink is being + printed. So rather than just using the output level of the + particular color to decide which ink to print, we look at the + total density (sum of all output levels). If the density's high + enough, we prefer to use the dark ink. Speckling is less + visible when there's a lot of ink, anyway. I haven't yet + figured out what to do for multiple levels of one color. + </P +><P +> You'll note that I haven't quoted a single source on color or + printing theory. I simply did all of this empirically. + </P +><P +> There are various other tricks to reduce speckling. One that + I've seen is to reduce the amount of ink printed in regions + where one color (particularly cyan, which is perceived as the + darkest) is very pale. This does reduce speckling all right, + but it also results in strange tonal curves and weird (to my + eye) colors. + </P +><P +> Before any dither routine is used, + <CODE +CLASS="function" +>init_dither</CODE +> must be called. This takes + three arguments: the input width (number of pixels in the + input), the output width (number of pixels in the output), and a + <SPAN +CLASS="type" +>stp_vars_t</SPAN +> structure containing the parameters for + the print job. + </P +><P +> <CODE +CLASS="function" +>init_dither</CODE +> returns a pointer to an opaque + object representing the dither. This object is passed as the first + argument to all of the dither-related routines. + </P +><P +> After a page is fully dithered, <CODE +CLASS="function" +>free_dither</CODE +> + must be called to free the dither object and perform any + cleanup. In the future, this may do more (such as flush + output). This arrangement permits using these routines with + programs that create multiple output pages, such as GhostScript. + </P +><P +> The dithering routines themselves have a number of control knobs + that control internal aspects of the dithering process. These + knobs are accessible via a number of functions that can be + called after <CODE +CLASS="function" +>init_dither</CODE +>. + </P +><P +></P +><UL +><LI +><P +> <CODE +CLASS="function" +>dither_set_density</CODE +> takes a double + between 0 and 1 representing the desired ink density for + printing solid colors. This is used in a number of places + in the dithering routine to make decisions. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_black_density</CODE +> takes a double + between 0 and 1 representing the desired ink density for + printing black ink in color printing. This is used to + balance black against color ink. By default, this is equal + to the density set by + <CODE +CLASS="function" +>dither_set_density</CODE +>. By setting it + higher, more black ink will be printed. For example, if the + base density is .4 and the black density is .8, twice as + much black ink will be printed as would otherwise be called + for. + </P +><P +> This is not used when printing in monochrome. When printing + monochrome, the base density + (<CODE +CLASS="function" +>dither_set_density</CODE +>) should be adjusted + appropriately. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_ink_budget</CODE +> takes an unsigned + number representing the most ink that may be deposited at a + given point. This number is arbitrary; the limit is + computed by summing the size of each ink dot, which is + supplied as a parameter in + <CODE +CLASS="function" +>dither_set_X_ranges</CODE +>. By default, there + is no limit. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_black_lower</CODE +> takes a double + that should be between 0 and 1 that represents the lowest + density level at which black ink will start to mix in with + colored ink to generate grays. The lower this is, the less + density is required to use black ink. Setting this too low + will result in speckling from black dots, particularly on 6 + and 7 color printers. Setting this too high will make it + hard to get satisfactory black or may result in sharp + transition between blended colors and black. Default: + 0.0468. + </P +><P +> It is important to note that since the density scale is + never linear (and since this value is adjusted via other + things happening during the dithering process) that this + does not mean that 95% gray will use any black ink. At this + setting, there will be no black ink used until about 50% + gray. + </P +><P +> This only applies to color mode. + </P +><P +> This value should be set lower for printers capable of + variable dot size, since more dots can be laid down close to + each other. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_black_upper</CODE +> takes a double + that should be between 0 and 1 that represents the highest + density level at which colored inks will be mixed to create + gray. Setting this too low will result in speckly dark + grays because there is not enough ink to fill all the holes, + or sharp transition between blended colors and black if it + is too close to the value of + <CODE +CLASS="function" +>dither_set_black_upper</CODE +> Setting this too + high will result in poor black and dark tone quality. + Default: 0.5. This results in 10% and darker grays being + printed with essentially all black. + </P +><P +> This only applies to color mode. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_black_levels</CODE +> takes three + doubles that represent the amount of cyan, magenta, and + yellow respectively that are blended to create gray. The + defaults are 1.0 for each, which is probably too low for + most printers. These values are adjusted to create a good + gray balance. Setting these too low will result in pale + light and midtone grays, with a sharp transition to darker + tones as black mixes in. Setting them too high will result + in overly dark grays and use of too much ink, possibly + creating bleed-through. + </P +><P +> This only applies to color mode. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_randomizers</CODE +> takes four + integer values representing the degree of randomness used + for cyan, magenta, yellow, and black. This is used to allow + some printing to take place in pale areas. Zero is the most + random; greater than 8 or so gives very little randomness at + all. Defaults are 0 for cyan, magenta, and yellow, and 4 + for black. Setting the value for black too low will result + in black speckling in pale areas. Setting values too high + will result in pale areas getting no ink at all. + </P +><P +> This currently only applies to single dot size in color and + black. It should be extended to operate in variable dot + size mode, although actually applying it correctly will be + tricky. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_ink_darkness</CODE +> takes three + doubles representing the contribution to perceived darkness + of cyan, magenta, and yellow. This is used to help decide + when to switch between light and dark inks in 6 and 7 color + printers (with light cyan, light magenta, and possibly light + yellow). Setting these too low will result in too much + light ink being laid down, creating flat spots in the + darkness curves and bleed-through. Setting them too high + will result in dark ink being used in pale areas, creating + speckle. The defaults are .4 for cyan, .3 for magenta, and + .2 for yellow. Dark cyan will show against yellow much more + than dark magenta will show against cyan, since the cyan + appears much darker than the yellow. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_light_inks</CODE +> takes three + doubles between 0 and 1 representing the ratio in darkness + between the light and dark versions of the inks. Setting + these too low will result in too much dark ink being used in + pale areas, creating speckling, while setting them too high + will result in very smooth texture but too much use of light + ink, resulting in flat spots in the density curves and ink + bleed-through. There are no defaults. Any light ink + specified as zero indicates that there is no light ink for + that color. + </P +><P +> This only applies to 6 and 7 color printers in single dot + size color mode, and only to those inks which have light + versions (usually cyan and magenta). + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_ink_spread</CODE +> takes a small + integer representing the amount of ink spread in the dither. + Larger numbers mean less spread. Larger values are + appropriate for line art and solid tones; they will yield + sharper transitions but more dither artifacts. Smaller + values are more appropriate for photos. They will reduce + resolution and sharpness but reduce dither artifacts up to a + point. A value of 16 or higher implies minimum ink spread + at any resolution no matter what the overdensity. A value + of 14 is typical for photos on single dot size, 6 color + printers. For 4 color printers, subtract 1 (more spread; + the dots are farther apart). For variable dot size + printers, add 1 (more small dots are printed; less spread is + desirable). + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_adaptive_divisor</CODE +> takes a + float representing the transition point between error + diffusion and ordered dither if adaptive dithering is used. + The float is a fraction of the printing density. For + example, if you wish the transition to be at 1/4 of the + maximum density (which works well on simple 4-color + printers), you would pass .25 here. With six colors and/or + with multiple dot sizes, the values should be set lower. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_transition</CODE +> takes a float + representing the exponent of the transition curve between + light and dark inks/dot sizes. A value less than 1 (typical + when using error diffusion) mixes in less dark ink/small + dots at lower ends of the range, to reduce speckling. When + using ordered dithering, this must be set to 1. + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_X_ranges_simple</CODE +> + (<TT +CLASS="literal" +>X</TT +> = <TT +CLASS="literal" +>c</TT +>, + <TT +CLASS="literal" +>m</TT +>, <TT +CLASS="literal" +>y</TT +> or + <TT +CLASS="literal" +>k</TT +>) describes the ink choices available + for each color. This is useful in typical cases where a + four color printer with variable dot sizes is in use. It is + passed an array of doubles between (0, 1] representing the + relative darkness of each dot size. The dot sizes are + assigned bit patterns (and ink quantities, see + <CODE +CLASS="function" +>dither_set_ink_budget</CODE +> above) from 1 to + the number of levels. This also requires a density, which + is the desired density for this color. This density need + not equal the density specified in + <CODE +CLASS="function" +>dither_set_density</CODE +>. Setting it lower + will tend to print more dark ink (because the curves are + calculated for this color assuming a lower density than is + actually supplied). + </P +></LI +><LI +><P +> <CODE +CLASS="function" +>dither_set_X_ranges</CODE +> + (<TT +CLASS="literal" +>X</TT +> = <TT +CLASS="literal" +>c</TT +>, + <TT +CLASS="literal" +>m</TT +>, <TT +CLASS="literal" +>y</TT +> or + <TT +CLASS="literal" +>k</TT +>) describes in a more general way the + ink choices available for each color. For each possible ink + choice, a bit pattern, dot size, value (i. e. relative + darkness), and whether the ink is the dark or light variant + ink is specified. + </P +></LI +></UL +></DIV +><DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +SUMMARY="Footer navigation table" +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="x1734.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="index.html" +ACCESSKEY="H" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="a2122.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Weaving algorithms</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +> </TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>GNU General Public License</TD +></TR +></TABLE +></DIV +></BODY +></HTML +>
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