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Re: Precise bitmaps

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96729] Re: Precise bitmaps
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Mon, 23 Feb 2009 05:01:16 -0500 (EST)
  • References: <gnq6ni$83g$1@smc.vnet.net>

Diamond, Mark wrote:
> A question was asked back in 2005 about precise bitmaps. I have a similar 
> question with regard to Mathematica version 7.
> 
> Looking at the new image-manipulation functions in V7, I expected this to be 
> quick ... I'd like to be able to create a series of stimuli for use in an 
> experiment. The first step in creating the stimuli is to create a 512 x 512 
> greyscale image with a white background and which contains the drawn 
> objects.
> 
> I tried the following to create a JPEG image with dimensions 128x128 ...
> 
> circ=Graphics[Circle[{0,0},62]]
> rasterCirc=Rasterize[circ,RasterSize->{128,128}]
> Export["circle.jpg",rasterCirc]
> 
> but instead the image dimensions are 360 x 363 pixels. I had also hoped that 
> I could obtain an antialiased arc but the only antialiasing option seems to 
> be for Style, which then produces a non-Graphics object.
> 
> Can anyone see a simple (i.e., not very low-level programming) solution to 
> the problem within Mathematica? What have I missed conceptually that would 
> explain the 360x363 pixel dimensions instead of my expected 128x128? And is 
> there a way to obtain the anti-aliased circle?
> 
> Cheers,
> 
> Mark Diamond
> 
> 
> 
The problem is that circ is a graphics object of much lower resolution - 
you have to force it to be the size that you want to rasterize:

circ = Graphics[Circle[{0, 0}, 62], ImageSize -> {512, 512}]
rasterCirc = Rasterize[circ, RasterSize -> {512, 512}]
Export["circle.jpg", rasterCirc]

David Bailey
http://www.dbaileyconsultancy.co.uk


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