Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.postscript > #2279 > unrolled thread

. alpha channel circles RGB overlapping

Back to article view | Back to comp.lang.postscript

Contents

  . alpha channel circles RGB overlapping jodun@mail.com - 2015-05-21 12:28 -0700
    Re: . alpha channel circles RGB overlapping ken <ken@spamcop.net> - 2015-05-22 07:55 +0100
      Re: . alpha channel circles RGB overlapping luser- -droog <mijoryx@yahoo.com> - 2015-06-12 19:10 -0700

#2279 — . alpha channel circles RGB overlapping

am baaa k

Hi  GHOSTSCRIPT gurus !

How to draw overlapping marks
of different RGB colors
every mark has half transparency


            say 

the famous 3 overlapping/intersecting circles
a red circle
a green circle
a blue

each circle of 50% opacity/transparency/alphachannelity
The 3 circles may intersect symmetrically (or not)

-
baaa

[toc] | [next] | [standalone]

#2280

In article <227f97c0-c204-4442-ba27-93402277cbde@googlegroups.com>, 
jodun@mail.com says...

> Hi  GHOSTSCRIPT gurus !

Ths is a PostScript group, not a Ghostscript group. PostScript is a 
language, Ghostscript is an interpreter for that language. There are 
other PostScript interpreters.

 
> How to draw overlapping marks
> of different RGB colors
> every mark has half transparency
> 
>             say 
> 
> the famous 3 overlapping/intersecting circles
> a red circle
> a green circle
> a blue
> 
> each circle of 50% opacity/transparency/alphachannelity
> The 3 circles may intersect symmetrically (or not)

If you read the PLRM you will see that PostScript does not support alpha 
channels. There is no support for transparency in PostScript, with a few 
exceptions;

1) Masked images and imagemasks. This involves either 0 or 100% opacity, 
so transparencym but not translucency.

2) overprint. Ths simply doesn't erase underlying marks when drawing new 
ones, so it doesn't do any alpha channel blending either. Also overprint 
is specified to only apply to CMYK colours, so you can't use it with RGB 
colourants.

The figure you describe would most easily be drawn as three circles, 
each of a different colour R, G or B, then the three segments where each 
overlaps would have to be drawn separatly with a different colour, and 
finally the segment where all three overlap would again be drawn as a 
separate operation.


			Ken

[toc] | [prev] | [next] | [standalone]

#2288

On Friday, May 22, 2015 at 1:55:33 AM UTC-5, ken wrote:
> In article <227f97c0-c204-4442-ba27-93402277cbde@googlegroups.com>, 
> jodun@mail.com says...
> 
> > Hi  GHOSTSCRIPT gurus !
> 
> Ths is a PostScript group, not a Ghostscript group. PostScript is a 
> language, Ghostscript is an interpreter for that language. There are 
> other PostScript interpreters.
> 
>  
> > How to draw overlapping marks
> > of different RGB colors
> > every mark has half transparency
> > 
> >             say 
> > 
> > the famous 3 overlapping/intersecting circles
> > a red circle
> > a green circle
> > a blue
> > 
> > each circle of 50% opacity/transparency/alphachannelity
> > The 3 circles may intersect symmetrically (or not)
> 
> If you read the PLRM you will see that PostScript does not support alpha 
> channels. There is no support for transparency in PostScript, with a few 
> exceptions;
> 
> 1) Masked images and imagemasks. This involves either 0 or 100% opacity, 
> so transparencym but not translucency.
> 
> 2) overprint. Ths simply doesn't erase underlying marks when drawing new 
> ones, so it doesn't do any alpha channel blending either. Also overprint 
> is specified to only apply to CMYK colours, so you can't use it with RGB 
> colourants.
> 
> The figure you describe would most easily be drawn as three circles, 
> each of a different colour R, G or B, then the three segments where each 
> overlaps would have to be drawn separatly with a different colour, and 
> finally the segment where all three overlap would again be drawn as a 
> separate operation.
> 

I wonder. Is there any way shfill could be used to 
calculate the blended colors? Some degenerate case
with interpolation over a constant function (so it
doesn't actually draw a gradient)?

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.postscript

csiph-web