How does Interpolation of Images work in level 2? (with broken example)

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2 total messages Started by Mike Hovan Tue, 11 Aug 1992 01:17

#259

Author: Mike Hovan
Date: Tue, 11 Aug 1992 01:17

37 lines
1361 bytes

	I have been playing around with some of the new features of  
level 2 PS for the last couple of weeks.  I came across the  
interpolation feature of images and I was wondering if anyone had  
some simple examples.  I have tried (in vain) to get an interpolated  
image to produce a different result than an uninterpolated image. 


	Here is what I have been using to test:

--CUT HERE----CUT HERE----CUT HERE----CUT HERE----CUT HERE--
%!PS-Adobe-3.0
/DeviceRGB setcolorspace
144 144 translate 144 144 scale
<<
	/ImageType 1
	/Width 2 /Height 2 
	/BitsPerComponent 8
	/MultipleDataSources true
	/ImageMatrix [2 0 0 -2 0 2]
	/Decode [0 1 0 1 0 1]
	/Interpolate true
	/DataSource [<FF 00 00 00> <00 FF 00 00> <00 00 FF 00>]
>>
image
--CUT HERE----CUT HERE----CUT HERE----CUT HERE----CUT HERE--


	If you have any suggestions or examples I would appreciate  
them.


	Thanks,

	Mike Hovan
	RDR, Inc.
	mhovan@rdr.com (NeXTMAIL accepted)

Re: How does Interpolation of Images work in level 2? (with broken example)

#1844

Author: Jim DeLaHunt
Date: Fri, 21 Aug 1992 04:27

44 lines
2210 bytes

In article <1992Aug11.011717.1588@rdr.com> mhovan@rdr.com writes:
>I was wondering if anyone had  
>some simple examples.  I have tried (in vain) to get an interpolated  
>image to produce a different result than an uninterpolated image. 

Try this:
--CUT HERE----CUT HERE----CUT HERE----CUT HERE----CUT HERE--
%!PS-Adobe-3.0
/DeviceGray setcolorspace
144 144 translate 144 144 scale
<<
	/ImageType 1
	/Width 8 /Height 8
	/BitsPerComponent 1
	/MultipleDataSources true
	/ImageMatrix [8 0 0 -8 0 8]
	/Decode [0 1]
	/Interpolate true
	/DataSource <FF 7F 3F 1F 0F 07 03 01>
>>
image
--CUT HERE----CUT HERE----CUT HERE----CUT HERE----CUT HERE--

On my LaserWriter IIg this code produces a dramatic difference between 
/Interpolate true and /Interpolate false.

The spec says (PLRM p. 222):
	"[The image interpolation algorithm] *attempts* to make a smooth 
	 transition between image values." [my emphasis]

In other words, neither the algorithm nor the range of cases when it is
applied is specified.  It seems that in the implementations you and I
are using, the algorithm is not applied for 24 bits-per-pixel images, but
is applied for 1 bit-per-pixel images.

There are many features of the PostScript language for which the interpreter
is *allowed* to make things better, but is not *required*.  Different 
implementations will do different things.  The trick is to not make your
code dependent on what any particular implementation does.

>	Mike Hovan, RDR, Inc., mhovan@rdr.com (NeXTMAIL accepted)

	--Jim DeLaHunt, Developer Support, Adobe Systems Incorporated	
delahunt@adobe.com	...!{apple,decwrl}!adobe!delahunt      +1-415-962-3790

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