| Re: 24-bit color Postscript [message #12729] |
Tue, 08 September 1998 00:00 |
Mark Hadfield
Messages: 783
Registered: May 1995
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Senior Member |
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> This is not the most lucid explanation I've even written (I've
> had a few beers to celebrate the worker's cause)
Actually, David, that is the most lucid explanation you've even [sic, hic]
written.
> , so let
> me know if you have any questions. :-)
What was the beer?
--
Mark Hadfield, m.hadfield@niwa.cri.nz http://www.niwa.cri.nz/~hadfield/
National Institute for Water and Atmospheric Research
PO Box 14-901, Wellington, New Zealand
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| Re: 24-bit color Postscript [message #12731 is a reply to message #12729] |
Mon, 07 September 1998 00:00  |
bowman
Messages: 121
Registered: September 1991
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Senior Member |
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In article <MPG.105cfb2b4b2f224e98969d@news.frii.com>, davidf@dfanning.com
(David Fanning) wrote:
> Well, you might think, since this is a 24-bit PostScript
> printer you've got here, that you can draw a line in a color
> like you would on your display device (I.e., specify the
> color as a 24-bit integer value).
> But, unfortunately, this does NOT work in PostScript.
> Even though you can display 24-bit color images in PostScript,
> you can't for some reason write 24-bit colors like this.
> In fact, you MUST use the INDEXED color model to draw a
> line in a color. But this is not much of a problem in a
> 24-bit world, since you aren't really using the color
> table for anything else.
My thanks to David. I have already replied to him by e-mail.
Is this a Postscript limitation or an IDL limitation? In either case, it
sucks. I need to plot points, not just images, using 24-bit color. That
is, I want to plot thousands of points using more than 256 different
colors. Is there no workaround for this?
I just spent a lot of time developing an IDL application only to find out
I can't print with it. You tell me if you could have learned that from
the description of the Postscript device in the reference manual.
I suppose I'll have to do a high-resolution X image and dump it to the
printer, which defeats the whole point of using Postscript.
Ken Bowman
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| Re: 24-bit color Postscript [message #12736 is a reply to message #12731] |
Sun, 06 September 1998 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Kenneth P. Bowman (bowman@null.tamu) writes:
> I have an IDL application that creates 24-bit X displays consisting of a
> grayscale image with points plotted on top in color using PLOTS. (Yes, it
> really is preferable to do this using 24-bit color.) Color works fine on
> the screen, but everything comes out grayscale in Postscript. This is
> direct graphics, BTW.
>
> I have read the Reference manual section on color Postscript, but it is
> less than clear. It only addresses color images, not 24-bit color created
> with things like PLOTS.
>
> My copy of David Fanning's book is at work, so I have not been able to
> check it (will do so in the morning).
>
> Any suggestions?
Buy another book for home.
Oh!? You mean about color PostScript? :-)
Well, you might think, since this is a 24-bit PostScript
printer you've got here, that you can draw a line in a color
like you would on your display device (I.e., specify the
color as a 24-bit integer value). For example, if I am
working on a 24-bit display with color decomposition turned
on and I want to draw a line in a yellow color, I would
type this:
PlotS, [0,1], [0,1], /Normal, Color=65635
Or, more likely, since I don't normally think in binary
arithmetic, I might type:
PlotS, [0,1], [0,1], /Normal, Color='00ffff'x
But, unfortunately, this does NOT work in PostScript.
Even though you can display 24-bit color images in PostScript,
you can't for some reason write 24-bit colors like this.
In fact, you MUST use the INDEXED color model to draw a
line in a color. But this is not much of a problem in a
24-bit world, since you aren't really using the color
table for anything else. (Your 24-bit image colors
were expressed *directly* through the actual
pixel values of the image and didn't go *through* the
color table.)
So, I can display a grayscale image and put a yellow
line on top of this image like this:
TV, image ; or TV, image24, True=1, etc.
TVLCT, 255, 255, 0, 10
PlotS, [0,1], [0,1], /Normal, Color=10
Device, /Close_File
This is not the most lucid explanation I've even written (I've
had a few beers to celebrate the worker's cause), so let
me know if you have any questions. :-)
Cheers,
David
----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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