Color/Spot Colors

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Spot Colors

To produce a file ready for a clean PDF separation process at your print house, start with:

\setupcolors[rgb=no,cmyk=yes,spot=yes,state=start,overprint=yes]

which will set things up for spot colors with CMYK allowed. The last setting ensures that black overprinting your spot colour tints will not knock out the colour - this is important for some types of commercial printing.

Then define your basic spot colour. Note that the name cannot contain spaces or numbers (but we come to that later):

\definecolor[PantoneTwoNineFour][c=1,m=.56,y=0,k=.18]

Now you can define the tints of this ink that you are actually going to use in your document. Let's say you'll have a 100% for headings:

\definespotcolor[MyBlue][PantoneTwoNineFour][p=1]

And then a 20% tint for nice display boxes:

\definespotcolor[MyBlueTint][PantoneTwoNineFour][p=.2]

And now you can happily use these named colours:

\starttext
   \color[MyBlue]{Interesting}
\stoptext

If you are including graphics made by an external program, you might want to match the colour name used in the graphic with the colour name in your ConTeXt set-up so that only one colour space is used in the final file. Unfortunately Pantone names and others tend to have spaces and numbers in them, so you need to do some extra work.

Using the 'e' key to \definespotcolor to specify a spot colour name with spaces

You can use the 'e' key when defining your spot colours in order to specify the precise colour names to be used by your ConTeXt set-up in the output file. For example:

% set up the cmyk fallbacks
\definecolor
   [PantoneThreeZeroEight]
   [c=1,m=.05,y=0,k=.47]

\definecolor
   [PantoneTwoNineEight]
   [c=.69,m=.07,y=0,k=0]

% Define tints of spot colours to be used in document for colouring text
\definespotcolor
   [DarkBlue]
   [PantoneThreeZeroEight]
   [p=1,e=PANTONE 308 CV]

\definespotcolor
   [LightBlue]
   [PantoneTwoNineEight]
   [p=1,e=PANTONE 298 CV]

(Tested only on minimal Linux distribution dated 8 May 2010 - can others confirm this to be true across the board now?)

Any text between a [[Command/startcolor[DarkBlue]|\startcolor[DarkBlue]]] and \stopcolor should now be assigned to the correct spot colour channel - Pantone 308 CV - on output. More importantly if you include an external figure containing areas of this colour then your text and those parts of the graphic which have the same colour should now appear together in the 'Pantone 308 CV' colour channel on colour separation.

For example, if your original graphic is an EPS file containing the following lines:

%%DocumentCustomColors: (PANTONE 298 CV)
%%+ (PANTONE 308 CV)
%%CMYKCustomColor: 0.69 0.07 0 0 (PANTONE 298 CV)
%%+ 1 0.05 0 0.47 (PANTONE 308 CV)

and you convert this to a PDF using ps2pdf for inclusion in your ConTeXt document your PDF graphic will then contain something like:


8 0 obj
[/Separation
/PANTONE#20308#20CV
/DeviceCMYK
9 0 R]endobj
10 0 obj
[/Separation
/PANTONE#20298#20CV
/DeviceCMYK
11 0 R]endobj

Note how the space characters in the colour name are now encoded as '#20', but the colour names are essentially identical between the original EPS graphic, the new PDF graphic and your text.

A good way of testing colour separation if you don't have access to expensive pre-flight PDF validation tools is to use the following GhostScript command:

gs \
  -dBATCH \
  -dNOPAUSE \
  -sDEVICE=tiffsep \
  -dDOINTERPOLATE \
  -dTextAlphaBits=4 \
  -dGraphicsAlphaBits=4 \
  -sOutputFile=output.tif \
  -r120 \
  -MaxSeparations=8 \
  input.pdf

This renders a PDF file input.pdf as a set of TIFF files:

  output.tif              - Composite including CMYK approximations to spot colours
  output.tif.Black.tif    - K channel
  output.tif.Cyan.tif     - C channel
  output.tif.Magenta.tif  - M channel
  output.tif.Yellow.tif   - Y channel
  output.tif.s0.tif       - Pantone 308 CV
  output.tif.s1.tif       - Pantone 298 CV

Multitones

Hans posted this example about spot and multitone colors on the mailinglist (2012-05-07). The interface has slightly changed in comparison to older versions. It is important to define the colorants as spot colors first (\definespotcolor).

\definecolor         [xcyan]   [c=1]
\definecolor         [xmagenta][m=1]
\definecolor         [xyellow] [y=1]

\definespotcolor     [scyan]   [xcyan]   [p=1]
\definespotcolor     [smagenta][xmagenta][p=1]
\definespotcolor     [syellow] [xyellow] [p=1]

\definemultitonecolor[scombi] [xcyan=.2,xmagenta=.4,xyellow=.6][c=.2,m=.4,y=.6]

\startTEXpage
    \hbox \bgroup
        \blackrule[color=scyan,   width=1cm,height=1cm,depth=0cm]%
        \blackrule[color=smagenta,width=1cm,height=1cm,depth=0cm]%
        \blackrule[color=syellow, width=1cm,height=1cm,depth=0cm]%
        \blackrule[color=scombi,  width=1cm,height=1cm,depth=0cm]%
    \egroup
\stopTEXpage

(The CMYK color spec is the fall back color used on screen; one can preview separations in full Acrobat 7.)

Colorizing Grayscale Pictures

Another sample by Hans (mailing list 2005-11-16) demonstrates a lot of different possibilities:

\setuplayout[header=0pt,footer=0pt,width=middle,height=middle,backspace=1cm,topspace=1cm]
\setupcolors[state=start]

\startbuffer
\definecolor [blue]   [c=1, m=.38, y=0, k=.64]
\definecolor [yellow] [c=0, m=.28, y=1, k=.06]

\definespotcolor [blue-100]   [blue]   [p=1]
\definespotcolor [yellow-100] [yellow] [p=1]

\definemultitonecolor [combicolor]   [blue=.12, yellow=.28] [c=.1, m=.1, y=.3, k=.1]

\definemultitonecolor [combicolor-b] [blue=1]   [c=1, m=.38, y=0, k=.64] % force multitone
\definemultitonecolor [combicolor-y] [yellow=1] [c=0, m=.28, y=1, k=.06] % force multitone

\useexternalfigure[demo-a][mill.png]     [object=no, width=.2\textwidth]
\useexternalfigure[demo-b][hacker-bw.jpg][object=no, width=.2\textwidth]

\startbaselinecorrection
\startcombination[4*1]
 {\externalfigure[demo-a]}                                {no color}
 {\externalfigure[demo-a][color=combicolor]}   {indexed duotone}
 {\externalfigure[demo-a][color=combicolor-b]} {spot color}
 {\externalfigure[demo-a][color=combicolor-y]} {spot color}
\stopcombination
\stopbaselinecorrection

\startbaselinecorrection
\startcombination[4*1]
 {\externalfigure[demo-b]}                     {no color}
 {\externalfigure[demo-b][color=combicolor]}   {indexed duotone}
 {\externalfigure[demo-b][color=combicolor-b]} {spot color}
 {\externalfigure[demo-b][color=combicolor-y]} {spot color}
\stopcombination
\stopbaselinecorrection

\startbaselinecorrection
\startcombination[4*1]
 {\externalfigure[demo-a]}                     {no color}
 {\externalfigure[demo-a][color=combicolor]}   {indexed duotone}
 {\externalfigure[demo-a][color=blue-100]}     {spot color}
 {\externalfigure[demo-a][color=yellow-100]}   {spot color}
\stopcombination
\stopbaselinecorrection

\startbaselinecorrection
\startcombination[4*1]
 {\externalfigure[demo-b]}                     {no color}
 {\externalfigure[demo-b][color=combicolor]}   {indexed duotone}
 {\externalfigure[demo-b][color=blue-100]}     {spot color}
 {\externalfigure[demo-b][color=yellow-100]}   {spot color}
\stopcombination
\stopbaselinecorrection
\stopbuffer

\getbuffer \typebuffer

\stoptext

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