Re: [NTG-context] metapost: remapping colors of an SVG picture

On 2/18/2020 12:18 PM, mf wrote:

Hello list, I tried this:

\starttext \startMPcode picture p ; p := lmt_svg [ filename = "sample.svg" ] ; draw p ; color black_rgb ; black_rgb := ( 0, 0, 0 ) ; color red_rgb   ; red_rgb   := ( 1, 0, 0 ) ; remapcolor( black_rgb, red_rgb ) ; recolor p ; draw p shifted ( bbwidth(p) + 5mm, 0) ; \stopMPcode \stoptext

\setupcolors[rgb=no] \startMPcode draw lmt_svg [ filename = "sample.svg" ] ; \stopMPcode

but recolor gives an error: metapost log    > >> picture metapost log    > ! Wrong picture color model: redpart of grey object. metapost log    > _f_:=(redpart(EXPR0), metapost log    > greenpart(EXPR0),bluepart(EXPR0));if.bou... metapost log    > metapost log    > repathed->...fi;fi;else:addto._p_.also.i;fi;endfor metapost log    > ;setbounds._p_.to._b_;_p_.... metapost log    > <to be read again> metapost log    >                    ; metapost log    > <*> ...apcolor( black_rgb, red_rgb ) ; recolor p ; metapost log    > draw grayed p shifted ( b... metapost log    >

My goal is to remap colors of an SVG image, like this:

\starttext \startMPcode picture p ; p := lmt_svg [ filename = "sample.svg" ] ; draw p ; color black_rgb      ; black_rgb  := ( 0, 0, 0 ) ; cmykcolor black_cmyk ; black_cmyk := ( 0, 0, 0, 1 ) ; remapcolor( black_rgb, black_cmyk ) ; recolor p ; draw p shifted ( bbwidth(p) + 5mm, 0) ; \stopMPcode \stoptext

It relates to a recent thread in the mailing list about color management. It's an attempt to use inkscape-made SVG graphics inside a CMYK workflow, without using color management.

Naturally it would work under some constraints, but there's a lot of graphics you can do with Inkscape that falls inside these: - the number of colors in the input SVG should be limited, so that every color gets converted - no embedded bitmaps, only vector graphics - perhaps some other constraints on gradients, transparency, etc.

A good alternative would be a remapper based on a custom lua function like this:

function rgb2cmyk( r, g, b )   ...   return c, m, y, k end

Massi

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