[Rd] image (PR#11493)

[Prof Brian Ripley]

The effect Duncan's picture shows is typical of using anti-aliasing for 
rectangles and polygons.  The cairo-based devices have it turned off for 
filled regions, as it seems to have no advantage for R uses of such 
regions.  (You also see it with some on-screen renderers of postscript or 
pdf versions of this plot, e.g. those based on ghostscript.)

However, this does not match the original report, so I think we need a 
reproducible example (with screenshot) from Joseph Scandura to make any 
further progress.

On Wed, 21 May 2008, Duncan Murdoch wrote:

> (Edited to add link to sample picture)
>
> Simon Urbanek wrote:
>> On May 20, 2008, at 8:05 PM, jms2003 at med.cornell.edu wrote:
>>
>> 
>>> Full_Name: Joseph Scandura
>>> Version: 2.7.0
>>> OS: Mac 10.5
>>> Submission from: (NULL) (140.251.50.94)
>>> 
>>> 
>>> Since updating to 2.7.0 all plots that use image() (heatmap, etc...) 
>>> now draw visible boxes around each rectangle in the plot. When there 
>>> are many rectangles the surrounding color becomes dominant over the 
>>> rectangle color and the overall image is borderline useless.
>>>
>>> 
>> 
>> Can you, please, specify exactly which graphics device you are using  and 
>> possibly a snapshot of the problem? I don't see any additional  boxes being 
>> drawn on any device.
>> 
>
> I see lines at the borders of the grid used by image on my Mac (Tiger, R
> 2.7.0 Patched (2008-05-20 r45743)).
> They are most visible in the last of the examples plotted by
> example(image), the one that starts
> image(x, y, volcano, col = terrain.colors(100), axes = FALSE).  It opens
> a Quartz device.
>
> How do you do a snapshot on a Mac?  I see online that it's Cmd-Shift-4,
> and I get the snapshot click, but I don't know where the picture ended up.
>
> AHA!  It goes to the desktop.
>
> Okay, a sample picture is available at
>
> http://www.stats.uwo.ca/faculty/murdoch/temp/grid.png
>
> Not as bad as Joseph was describing, but not nearly as good as Windows 
> produces ;-).
>
>
>> The only issue I'm aware of are anti-aliasing effects around the edges  of 
>> adjacent rectangles which don't fall on the pixel boundary (if anti- 
>> aliasing device is used). Depending on the subpixel location of the  edge, 
>> the background color may shine through very slightly. It's not  what you 
>> describe, but it's closest to what I can imagine you could  mean. However, 
>> AFAICS this has not been changed recently and is a  rendering artifact 
>> which is hard to get rid of in the current setup as  devices are 
>> resolution-independent (the only cure I'm aware of [short  of disabling 
>> anti-aliasing]  is to distort the original plot such that  rectangles are 
>> aligned with the pixels of the output medium).
>> 
> I don't know if what I'm seeing is new or not; I've only got one R
> version installed.
>
> Duncan Murdoch
>> Cheers,
>> Simon
>> 
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>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595