| Re: Beginner Question: PlotS rasterization info? [message #27794 is a reply to message #27789] |
Wed, 07 November 2001 14:20   |
sandy
Messages: 6
Registered: July 1991
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Junior Member |
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> Greetings Ted (Sandy?)--
>
> If it's really important to you to have exactly the same pixels on the
> screen and in your array, then probably your pixmap/WHERE approach is
> the most reliable.
>
> If you already have the Bresenham algorithm coded, then what reason is
> there to use PLOTS? In other words, why not plot the pixel values you
> determined from the Bresenham, and then you can be sure you know them
> exactly?
>
> Craig
>
Thanks David and Craig,
It's Ted--Sandy is just the default name on this computer.
It is important to have the same pixels on the screen. I'm using a modified
CW_DefRoi function to draw multiple regions of interests on multiple frames
of QuickTime movies. The modified function only returns the vertices of the
region of interest (instead of the subscripts of the interior). These ROIs
may overlap one another, but I want to be able to select and erase one or
some of them without erasing any pixels of the others from the screen. So I
can't just use Device, Copy, the way I understand it. I also need to
extract data from the frames at the pixel coordinates of the boundaries in
order to analyze them, not just to replace/erase the ROI data with the
original image data.
I've thought about just plotting everything with the Bresenham like Craig
suggests, but that would require further modifications to the CW_DefRoi
function, since it almost surely uses the IDL Plot algorithm. It would also
mean that for the sake of consistency future versions of the program could
not use IDL's plot function either, and I'm not comfortable with that, since
IDL's Plot is certainly much more reliable than my 15 lines of Bresenham
code. I haven't actually overplotted results from David's approach on a
PlotS line yet, but I'm thinking this technique will probably have the same
roundoff problems as the Bresenham--I'll check on it. But what algorithm is
IDL using to plot lines, anyway?
I don't have that strong computer programming background--LabVIEW and one C
programming course. I get the feeling I'm re-inventing the wheel. Now that
I've described the program in greater detail, is there a better way?
Thanks,
Ted
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