targen
Author: Graeme Gill

## target/targen

### Summary

Generate a profiling test target values .ti1 file. targen is used to generate the device channel test point values for grayscale, RGB, CMY, CMYK or N-color output or display devices.

### Usage Summary

targen [options] outfile
-v [level] Verbose mode [optional verbose level, 1..n]
-d col_comb choose colorant combination from the following:
0: Video grey
1: Print grey
2: Print CMY
3: Video RGB
4: CMYK
5: CMYK + Light CM
6: CMYK + Light CMK
7: CMYK + Red + Blue
8: CMYK + Orange + Green
9: CMYK + Light CMK + Light Light K
10: CMYK + Orange + Green + Light CM
11: CMYK + Light CM + Medium CM
-D colorant Add or delete colorant from combination:
0: Additive
1: Cyan
2: Magenta
3: Yellow
4: Black
5: Orange
6: Red
7: Green
8: Blue
9: White
10: Light Cyan
11: Light Magenta
12: Light Yellow
13: Light Black
14: Medium Cyan
15: Medium Magenta
16: Medium Yellow
17: Medium Black
18: Light Light Black
-G Generate good optimzed points rather than Fast
-e patches White color test patches (default 4)
-s steps Single channel steps (default 0)
-g steps Gray axis RGB or CMY steps (default 0)
-m steps Multidimensional device space cube steps (default 2)
-f patches Add iterative & adaptive full spread patches to total (default 836)
Default is Optimised Farthest Point Sampling (OFPS)
-t Use incremental far point for full spread
-r Use device space random for full spread
-R Use perceptual space random for full spread
-q Use device space-filling quasi-random for full spread
-Q Use perceptual space-filling quasi-random for full spread
-i Use device space body centered cubic grid for full spread
-I Use perceptual space body centered cubic grid for full spread
-a angle Simplex grid angle 0.0 - 0.5 for B.C.C. grid, default -2047840407
-A adaptation Degree of adaptation of OFPS 0.0 - 1.0 (default 0.1, 1.0 if -c profile provided)
-t Use incremental far point for full spread (default iterative)
-l ilimit Total ink limit in %(default = none, or estimated from profile)
-p power Optional power applied to all device values.
-c profile Optional device ICC or MPP pre-conditioning profile filename
-F L,a,b,rad Filter out samples outside Lab sphere.
-w Dump diagnostic outfile.wrl file (Lab locations)
-W Dump diagnostic outfile.wrl file (Device locations)
outfile Base name for output(.ti1)

### Usage Details and Discussion

The number of target patches needs to be chosen, depending on the media size, the type of device, and the quality of profile required. For an inkjet device, something like 3000 test points or more is desirable for high quality profiles, while 500-1000 will probably suffice for a medium quality profile. A few hundred may be sufficient for a preliminary profile. Well behaved printing devices (such as a chemical proof, or a high quality printing press) may produce good profiles with 1000 to 2000 test points. Well behaved RGB devices such as CRT monitors may need only a few hundred points, if a shaper/matrix type profile is to be produced, while pseudo RGB printers, or other RGB devices that a CLUT type profile may be used with, should probably choose somewhere between 500 and 3000 patches. For n color profile creation, 3000 or more test points should probably be used.
The -v flag turns on extra verbosity when generating patch values. Extra diagnostics and verbosity may be available if a parameter is provided with a value greater than 1.
The -d parameter sets the colorspace the test values will be generated in. Video gray space is assumed to be an additive space, where a zero device value will be black, and a maximum device value will be white. A print gray space is assumed to be a subtractive space, in which a zero device value will be white, and a maximum device value will be black. If no colorspace is specified, subtractive CMYK is assumed as a default.
The -D parameter modifies the colorspace set by -d by allowing individual colorants to be added or subtracted from the colorspace.
The -G flag changes the Incremental Far Point Distribution algorithm from fast to good mode. Fast mode uses a limited number of iterations to optimize the patch locations, while good mode strives for a more even patch distribution by using more iterations.
The composition of the test patches is controlled by the following flags and parameters:
The -e parameter sets the number of white colored test patches, defaulting to 4 if the -e flag isn't used. The white patches are usually very important in establishing white point that the ICC data is made relative to, so it improves robustness to use more than a single point.
The -s parameter sets the number of patches in a set of per colorant wedges. The steps are evenly spaced in device space by default, and the total number of test patches will be the number of colorants times the value specified with the -s flag. If the -p parameter is provided, then, then the steps will be distributed according to the power value. e.g. the option -s 5 will generate steps at 0.0 0.25 0.5 0.75 and 1.0, while the option -s 5 -p 2.0 will generate steps at 0.0 0.125 0.25 0.5625 and 1.0. By default, no per colorant test wedge values are generated. When creating a test chart for a device that will be used as a source colorspace, it is often useful to generated some per colorant wedge values.
The -g parameter sets the number of patches in a set of combined (nominally gray) wedges. This will typically be equal RGB or CMY values, and by default will be equally spaced steps in device space. If the -p parameter is provided, then, then the steps will be distributed according to the power value. e.g. the option -g 5 will generate steps at 0.0 0.25 0.5 0.75 and 1.0, while the option -g 5 -p 2.0 will generate steps at 0.0 0.125 0.25 0.5625 and 1.0. By default, no gray combination values are generated. When creating a test chart for a device that will be used as a source colorspace, it is often useful to generated some per colorant wedge values.
The -m parameter sets the edge size of the multidimensional grid of test values. The total number of patches of this type will be the -m parameter value to the power of the number of colorants. The grid steps are evenly spaced in device space by default, but if the -p parameter is provided, then, then the steps will be distributed according to the power value. e.g. the option -m 5 will generate steps at 0.0 0.25 0.5 0.75 and 1.0, while the option -m 5 -p 2.0 will generate steps at 0.0 0.125 0.25 0.5625 and 1.0. By default, all the device primary color combinations that fall within the ink limit are generated..
The behavior of the -e, -s, -g and -m flags, is not to duplicate test values already created by a previous type.
The -f parameter sets the number of full spread test patches. Full spread patches are distributed according to the default or chosen algorithm. The default algorithm will optimize the point locations to minimize the distance from any point in device space, to the nearest sample point. This is called Optimized Farthest Point Sampling (OFPS) . This can be overridden by specifying the -t. -r, -R, -q, -i or -I flags. If the default OFPS algorithm is used, then adaptive test point distribution can be enabled by specifying a non-zero value for the -A parameter, which sets the degree of adaptation. A value of 1.0 distributes the test points so as to minimize the estimated error in the resulting profile. A value less than 1.0 is generally recommended - e.g. try starting with a value of 0.5. Currently if a value of greater than 0.0 is use, the distribution is not as highly optimized as it is when the default 0.0 is used. The total number patches specified will include any patches generated using the -e, -s, -g and -m flags (i.e. full spread patches will be added to bring the total number of patches including those generated using the -e, -s, -g and -m flags up to the specified number). When there are more than four device channels, the full spread distribution algorithm can't deal with so many dimensions, and targen falls back on an incremental far point distribution algorithm by default, that doesn't generate such evenly spread points. This behaviour can be forced using the -t flag. A table of useful total patch counts for different paper sizes is shown below.
The -t flag overrides the default full spread test patch algorithm, and makes use of the Incremental Far Point Distribution algorithm, which incrementally searches for test points that are as far away as possible from any existing points. This is used as the default for dimensions higher than 4.
The -r flag overrides the default full spread test patch algorithm, and chooses test points with an even random distribution in device space.
The -R flag overrides the default full spread test patch algorithm, and chooses test points with an even random distribution in perceptual space.
The -q flag overrides the default full spread test patch algorithm, and chooses test points with a quasi-random, space filling distribution in device space.
The -Q flag overrides the default full spread test patch algorithm, and chooses test points with a quasi-random, space filling distribution in perceptual space.
The -i flag overrides the default full spread test patch algorithm, and chooses test points with body centered cubic distribution in device space.
The -I flag overrides the default full spread test patch algorithm, and chooses test points with body centered cubic distribution in perceptual space.
The -a angle parameter sets the overall angle that the body centered grid distribution has.
The -A adaptation parameter sets the degree of adaptation to the known device characteristics, used by the default full spread OFPS algorithm. A profile should be provided using the -c parameter if adaptation is set above a low level. By default the adaptation is 0.1 (low), and 1.0 (maximum) if -c profile is provided
The -l flag and parameter sets a total ink limit (Total Area Coverage or TAC), which is adhered to for all the generated points. It is generally good practice to set a test chart ink limit at least 10% higher than the ink limit that will be applied when making the resulting profile. In the case of device cube points, this can generate extra test values that lie at the ink limit boundary. For gray wedge values, any that exceed the ink limit are omitted. Full spread test values are all generated to lie within the ink limit. Although it doesn't make much sense, this parameter has an affect on additive device spaces (such as RGB), but should not normally be used with such devices. The total ink limit value will be written to the .ti1 file, and carried through automatically to the .ti3 file, so that it can be used during profile creation. If a profile is provided using the -c flag, then this will be used to estimate an ink limit, if none is provided with the -l flag. Ink limits are, as far as possible, always in final calibrated device values, and the calibration curves from the profile provided to the -c flag will be used to estimate the equivalent limit in the underlying pre-calibration device space values that targen creates.
The -p flag and parameter sets a power value applied to all of the device values after they are generated, the spacer colors. This can be useful in creating calibration charts for very non-linearly behaved devices. A value greater than 1.0 will cause a tighter spacing of test values near device value 0.0, while a value less than 1.0 will cause a tighter spacing near device value 1.0. [ Note that for Print RGB space this is reversed, since internally a Print RGB space is treated as a CMY space. ]. Note that the device model used to create the expected patch values will not take into account the applied power, nor will the more complex full spread algorithms correctly take into account the power in generating values up to the ink limits.
The -c flag and parameter is used to specify an ICC or MPP pre-conditioning profile, for estimating perceptual distances and colorspace curvature, used in optimizing the full spread test point placement,or in creating perceptualy spaced distributions. Normally a previous profile for this or a similar device will be used, or a simpler, preliminary profile will be created and used. If no such profile is specified, a default device space model is used. Note that this will only have an effect if an algorithm that uses the perceptual placement, such as -R, -Q, -I, or the default OFPS with an -A value > 0.0.
The -F flag and parameters is used to define an L*a*b* sphere to filter the test points through. Only test points within the sphere (defined by it's center and radius) will be written to the .ti1 file. This can be good for targeting supplemental test points at a troublesome area of a device. The accuracy of the L*a*b* target will be best when the -c option is used to specify a reasonably accurate profile for the device. Note that the actual number of points generated can be hard to predict, and will depend on the type of generation used. All means of generating points except the -f N & -r, -R and -q will generate a smaller number of test points than expected. If the -f N & -r, -R and -q methods are used, then the target number of points will be achieved. For this reason, the -f N -q method is probably the easiest to use.
The -w flag causes a diagnostic VRML .wrl file to be created, in which the test points are plotted as small spheres in L*a*b* colorspace. Note that for a CMYK device, the point spacing may seem strange, since the extra K dimension is compressed into the 3 dimensional L*a*b* space. If the -W flag is given, the plot will be in device space, with only the first 3 dimensions of each point being plotted.
The final parameter on the command line is the base filename for the .ti1 output file. targen will add the .ti1 extension automatically.
Some typical total patch number/paper size combinations are shown below. These "magic" numbers are found by using printtarg to compute the row length and number of rows, and then adjusting the total number of patches to fill the last row or paper size, in an iterative fashion.
Size (mm/Standard Name), No. Patches
DTP20:
1 x A4 540
2 x A4 1080
3 x A4 1620
4 x A4 2160
1 x Letter 570
2 x Letter 1140
3 x Letter 1710
4 x Letter 2280
DTP 22:
1 x A4 782
2 x A4 1564
1 x Letter 736
2 x Letter 1472
DTP41:
1 x A4 375
2 x A4 750
3 x A4 1125
4 x A4 1500
1 x Letter 345
2 x Letter 690
3 x Letter 1035
4 x Letter 1380
1 x A3 836
2 x A3 1672
1 x 11x17 780
2 x 11x17 1560
DTP51:
1 x A4 266
2 x A4 532
3 x A4 798
4 x A4 1064
1 x Letter 252
2 x Letter 504
3 x Letter 756
4 x Letter 1008
1 x A3 580
2 x A3 1160
1 x 11x17 570
2 x 11x17 1140
SpectroScan with square patches:
1 x A4R 1014
2 x A4R 2028
3 x A4R 3042
4 x A4R 4056
1 x LetterR 999
2 x LetterR 1998
3 x LetterR 2997
4 x LetterR 3996
SpectroScan with hexagonal patches:
1 x A4R 1170
2 x A4R 2340
3 x A4R 3510
4 x A4R 4680
1 x LetterR 1092
2 x LetterR 2184
3 x LetterR 3276
4 x LetterR 4368
Eye-One Pro:
1 x A4 441
2 x A4 882
3 x A4 1323
4 x A4 1764
1 x Letter 462
2 x Letter 924
3 x Letter 1386
4 x Letter 1848
Acquisition device (printtarg with -iSS -s options):
1 x A4R 1014
2 x A4R 2028
3 x A4R 3042
4 x A4R 4056
1 x LetterR 962
2 x LetterR 1924
3 x LetterR 2886
4 x LetterR 3848