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I'm working on a php project where I need to perform some pdf manipulation.

I need to "convert" all colors of a vector file(pdf) into one very specific color (a spot color in my case.)

Here is an illustrated example

example

The input file can vary, and it can contain any color (so I can't just convert all "red" or "green" to my target color).

I have a fair idea on how to do it on a raster image using imagemagick's composite, but I'm unsure if it's even possible with a vector image.

My first approach was to create a template pdf, with a filled rectangle in the desired color. My hope was then to use ghostscript to somehow apply the input file as a mask on said template. But I assume this wouldn't be possible as vector files are different from raster images.

My second approach was to use ghostscript to convert all colors (regardless of colorspace) into the desired color. But after extensive googling, I've only found solutions that convert from one colorspace to another (i.e. sRGB to CMYK, CMYK to gray-scale, etc.)

I'm not much of a designer, so perhaps I am simply lacking the proper "terms" for these "actions".

TL;DR

I am looking for a library/tool that can help me "convert" all colors of a vector file(pdf) into one very specific color.

  • The input file may vary (various shapes and colors), but will always be a pdf file without any fonts.
  • Output must remain as a vector file (read, no rasterisation.)
  • I have root access on a VPS running linux (centos7, I assume that is irrelevant.)
Community
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deshiv
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    If you are converting all colours to one specific output colour, how come your sample output image has two different shades of green and one of white? I make that three. ImageMagick will rasterise it, so you may as well remove it from the tags if rasterisation is unacceptable. – Mark Setchell Apr 11 '17 at 16:29
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    Actually 891 different colors, when you llok at the anti-aliasing pixels. – xenoid Apr 11 '17 at 17:53
  • How about rasterising at a high resolution and converting the colours with **ImageMagick**, then re-vectorising with **potrace**? One line of code, no Postscript to learn... – Mark Setchell Apr 12 '17 at 08:08
  • @MarkSetchell that's an interesting idea, I didn't know vectorising was even a word :) I might take a look at potrace before diving deeper – deshiv Apr 12 '17 at 08:32

2 Answers2

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You could do this with Ghostscript, but you would need some PostScript programming experience.

Essentially you want to override all the setcolor/setcolorspace operations by looking at each setcolor operation, checking the colour space and values to see if its your target colour and, if it is, set the colorspace and values to your desired target.

The various PDF operations to set colour space and values are all defined in ghostpdl/Resource/Init/pdf_draw.ps. You'll need to modify the definitions of:

/G and /g (stroke and fill colours in DeviceGray) /RG and /rg (stroke and fill colours in DeviceRGB) /K and /k (stroke and fill colours in DeviceCMYK) /SC and /sc (stroke and fill colours in Indexed, CalGray, CalRGB or Lab) /SCN and /scn (stroke and fill colours in Pattern, Separation, DeviceN or ICCBased)

There are quite a few wrinkles in there;

You can probably ignore Pattern spaces and just deal with any colours that are set by the pattern itself.

For SC/sc and /SCN/scn you need to figure out whether the colour specified is the target colour, assuming your target can be specified in these spaces. Note that /Indexed is particularly interesting as it can have a base space of any of the other spaces, so you need to look and see.

Finally note that images (bitmaps) are specified differently, and altering those would be much harder.

Depending on the exact nature of the requirement (ie what space/colours constitute valid targets) this could be quite a lengthy task, and it will require someone with PostScript programming ability to write it.

Oh, and on a final note, have you considered transparency ? That can specify the blending colour space too, which might mean that after you had substituted the colour, it would be blended in a different colour space, resulting in your careful substitution disappearing.

Lest you think this unlikely I should mention that a number of PDF producers create files with transparency groups in them, even when no actual transparency operations take place.

KenS
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  • Thanks for your descriptive reply! From your description, it does sound like a lengthy task indeed. I had not given transparency any though, was hoping that it could be completely ignored, as I'm more concerned about the shapes having a color rather than what the color is. I assume that my next step is to get into PostScript programming – deshiv Apr 12 '17 at 06:50
  • There actually is even more to consider. There are e.g. various blend modes for which one should *not* simply replace any coloring operation by one with the desired color. And transfer functions have to be considered. And some more pesky details... – mkl Apr 12 '17 at 07:26
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You could try rasterising at a high resolution and converting the colours with ImageMagick, then re-vectorising with potrace

So, if you had a PDF, you would do:

convert -density 288 document.pdf ...

As you have provided a PNG, I will do:

convert image.png -fill black -fuzz 10% +opaque white pgm:- | potrace -b svg -o result.svg -

which gives this SVG:

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
 "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
<svg version="1.0" xmlns="http://www.w3.org/2000/svg"
 width="800.000000pt" height="450.000000pt" viewBox="0 0 800.000000 450.000000"
 preserveAspectRatio="xMidYMid meet">
<metadata>
Created by potrace 1.13, written by Peter Selinger 2001-2015
</metadata>
<g transform="translate(0.000000,450.000000) scale(0.100000,-0.100000)"
fill="#000000" stroke="none">
<path d="M4800 4324 c0 -50 -2 -55 -17 -49 -84 35 -140 -17 -130 -119 7 -77
70 -120 122 -82 16 11 21 11 33 0 7 -8 18 -12 23 -9 5 4 9 76 9 161 0 147 -1
154 -20 154 -18 0 -20 -7 -20 -56z m-22 -90 c46 -32 18 -134 -38 -134 -25 0
-40 29 -40 79 0 39 19 71 43 71 7 0 23 -7 35 -16z"/>
<path d="M4926 4358 c-9 -12 -16 -35 -16 -50 0 -18 -5 -28 -15 -28 -8 0 -15
-7 -15 -15 0 -8 7 -15 15 -15 12 0 15 -17 15 -89 0 -89 6 -105 38 -94 8 3 12
31 12 94 0 88 0 89 25 89 16 0 25 6 25 15 0 9 -9 15 -25 15 -21 0 -25 5 -25
30 0 30 7 34 43 30 13 -1 18 4 15 17 -5 29 -72 30 -92 1z"/>
<path d="M3347 4364 c-4 -4 -7 -16 -7 -26 0 -14 6 -19 23 -16 14 2 22 10 22
23 0 20 -25 32 -38 19z"/>
<path d="M4170 4310 c0 -23 -4 -30 -20 -30 -11 0 -20 -7 -20 -15 0 -8 9 -15
20 -15 18 0 20 -7 20 -80 0 -74 2 -81 25 -96 32 -21 75 -12 75 17 0 16 -4 19
-21 14 -30 -10 -39 9 -39 83 l0 62 30 0 c20 0 30 5 30 15 0 10 -10 15 -30 15
-27 0 -30 3 -30 30 0 23 -4 30 -20 30 -16 0 -20 -7 -20 -30z"/>
<path d="M3345 4278 c-3 -8 -4 -59 -3 -114 2 -80 6 -99 18 -99 12 0 15 19 15
109 0 79 -4 111 -12 113 -7 3 -15 -2 -18 -9z"/>
<path d="M3453 4283 c-9 -3 -13 -34 -13 -108 0 -74 4 -105 13 -108 29 -10 37
6 37 78 0 57 4 75 18 88 46 42 72 10 72 -91 0 -54 4 -71 15 -76 22 -8 26 10
23 104 -3 77 -5 84 -31 104 -24 17 -32 19 -59 8 -18 -6 -38 -8 -47 -3 -9 5
-22 6 -28 4z"/>
<path d="M3687 4283 c-4 -3 -7 -71 -7 -150 l0 -143 25 0 c23 0 25 4 25 45 0
42 2 45 19 35 33 -17 61 -11 92 19 24 25 29 37 29 81 0 95 -51 141 -119 107
-25 -13 -31 -13 -35 -1 -6 15 -19 18 -29 7z m122 -47 c19 -22 23 -78 9 -106
-29 -55 -88 -26 -88 43 0 62 48 100 79 63z"/>
<path d="M3927 4284 c-4 -4 -7 -45 -7 -91 0 -76 2 -86 25 -108 27 -28 61 -32
92 -10 18 13 22 13 27 0 3 -8 12 -12 21 -9 13 5 15 24 13 113 -3 98 -4 106
-23 106 -18 0 -20 -8 -23 -75 -4 -94 -28 -128 -72 -100 -10 6 -16 34 -20 91
-5 75 -15 101 -33 83z"/>
<path d="M4432 4282 c-9 -7 -12 -43 -10 -148 3 -136 4 -139 26 -142 20 -3 22
1 22 41 l0 45 35 -11 c31 -9 39 -8 63 10 37 27 54 83 42 136 -15 68 -64 94
-120 63 -20 -12 -26 -12 -35 0 -6 8 -15 10 -23 6z m122 -54 c22 -31 20 -81 -3
-109 -19 -23 -21 -23 -48 -9 -24 13 -28 23 -31 62 -3 39 1 49 20 62 30 22 44
20 62 -6z"/>
<path d="M4310 4096 c0 -30 30 -43 47 -21 16 23 5 45 -23 45 -19 0 -24 -5 -24
-24z"/>
<path d="M4046 3795 l-67 -141 -227 -12 c-418 -22 -765 -74 -1127 -167 -612
-157 -1080 -387 -1387 -684 -214 -205 -323 -393 -359 -615 -16 -101 -6 -270
20 -361 136 -461 637 -856 1409 -1111 152 -51 434 -125 583 -154 l66 -13 -30
-169 c-16 -93 -27 -171 -24 -174 2 -3 124 58 271 135 l266 140 80 -9 c44 -5
197 -14 339 -21 259 -12 617 -3 844 21 l88 9 265 -140 c146 -77 268 -138 270
-136 5 4 -41 294 -52 328 -4 13 8 19 58 28 465 89 939 260 1278 461 626 370
880 871 686 1356 -69 174 -228 375 -415 526 -517 418 -1411 697 -2402 750
l-226 12 -71 141 -70 140 -66 -140z m-202 -407 c-31 -62 -119 -241 -196 -398
-76 -156 -140 -285 -142 -287 -3 -3 -799 -120 -1156 -170 -102 -14 -188 -29
-193 -32 -4 -4 102 -113 235 -242 133 -129 353 -344 489 -479 l248 -245 -45
-260 c-25 -143 -58 -332 -73 -420 l-27 -160 -41 2 c-61 2 -333 68 -515 124
-674 209 -1153 533 -1334 905 -59 121 -77 209 -71 349 5 137 35 235 109 359
58 97 206 261 311 344 463 366 1242 627 2097 701 69 6 141 13 160 15 19 1 72
4 118 4 l82 2 -56 -112z m906 86 c760 -79 1420 -283 1875 -581 864 -566 763
-1326 -245 -1840 -266 -136 -602 -253 -942 -328 -92 -21 -173 -35 -181 -32 -9
3 -20 44 -31 114 -10 59 -42 248 -72 419 l-54 311 213 210 c116 115 337 331
489 479 153 148 274 271 270 275 -4 3 -106 20 -227 37 -452 64 -1118 162
-1120 164 -6 6 -195 387 -291 587 l-104 214 137 -7 c76 -4 203 -14 283 -22z
m-424 -2761 c137 -73 200 -111 193 -118 -14 -14 -794 -14 -809 1 -7 7 49 41
192 117 112 58 207 107 212 107 5 0 100 -48 212 -107z"/>
<path d="M1815 3669 c-46 -47 -113 -80 -221 -111 -62 -17 -106 -22 -204 -22
-137 0 -185 12 -221 58 -48 61 -211 80 -449 53 -118 -14 -400 -63 -408 -72 -3
-3 28 -145 32 -145 1 0 55 11 120 25 181 37 365 58 481 53 98 -3 105 -5 125
-30 113 -144 579 -119 806 44 50 35 109 108 97 118 -5 4 -33 21 -63 38 l-55
31 -40 -40z"/>
<path d="M7647 575 c-66 -79 -247 -137 -432 -138 -134 0 -170 10 -221 61 -18
17 -53 37 -84 46 -70 21 -238 21 -395 0 -122 -15 -364 -60 -372 -68 -5 -5 17
-119 26 -133 4 -7 47 -2 121 13 181 37 358 56 477 52 l108 -3 37 -37 c120
-117 482 -110 720 13 75 40 168 123 168 151 0 10 -110 80 -122 77 -2 0 -16
-16 -31 -34z"/>
</g>
</svg>

which looks like this as a PNG (because StackOverflow doesn't allow SVG images AFAIK):

enter image description here

You can make all the PATHs your preferred shade of green by editing the SVG, like this:

sed 's/path /path fill="#7CBE89" /' black.svg > green.svg

enter image description here

Mark Setchell
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  • This is pretty close to what I wanted to achieve, although it doesn't seem to be possible to define cmyk or named spot colors in svg (from what I've read.) Do you know of an alternative format? – deshiv Apr 12 '17 at 14:12
  • We are at (ok, beyond) the limits of my knowledge! This refers... http://stackoverflow.com/q/3405689/2836621 – Mark Setchell Apr 12 '17 at 15:18