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writing gray scale GIFs from a 24bit machine [message #18814]

Fri, 04 February 2000 00:00

reardonb
Messages: 16
Registered: December 1999

Junior Member

Hi,
I'm having trouble creating gray scale GIF images that accurately
reflect what is on my screen. I'm using a Mac and this problem does not
exist when the colors are set to 256 but if the colors are set to
thousands or millions I get a saved GIF image that has one color band
that should be almost black but is instead almost white. I get this
problem for gray scale color pallets such as loadct, 0. If I set the
color pallet to loadct, 39 the saved GIF is very much like the screen
image. The code I am using is the one David Fanning suggested and is
attached below. I would like for this code to work on any system with
any color pallet and any monitor color setting. Any help would be
appreciated.
Thanks.
-Brian

device, decomposed=0
loadct, 0, ncolors=20, bottom=0
wset, info.wid
device, Get_visual_depth=thisdepth
if thisdepth gt 8 then begin
image24=TVRD(True = 1)
snapshot=color_quan(image24,1,r,g,b)
endif else begin
snapshot = tvrd()
tvlct, r, g, b, info.bottom, /get
endelse
write_gif,filename+'.gif',snapshot, r, g, b

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[Message index]

		writing gray scale GIFs from a 24bit machine By: reardonb on Fri, 04 February 2000 00:00
		Re: writing gray scale GIFs from a 24bit machine By: davidf on Mon, 07 February 2000 00:00
		Re: writing gray scale GIFs from a 24bit machine By: Liam E. Gumley on Mon, 07 February 2000 00:00

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