Starting at square one with image processing
sanke at hrz.uni-kassel.de
Mon Jul 9 12:08:45 CDT 2007
On Sun Jul 8, James Hurley jhurley0305 at sbcglobal.net wrote:
> Second: It is also clear, on closer inspection, that Run Rev is not
> fast enough for user created paint tools such as a pencil or brush.
> The poor man's pencil I described earlier is hit and miss if the
> pencil is moved too fast. I presume this is because it takes too long
> to continually reset the imagedata as the mouse is moved. Best to
> stick to button commands it seems.
your inventive script for the pencil tools proves once more that there
are more than one or two approaches to achieve specific effects in
x-talk languages. This is what most of us appreciate very much, and it
surely challenges the creativeness of x-talk programmers.
After the wonderful sunny Sunday - fine weather is rare these days in
the middle of Europe - I took a second look at the various questions and
put together a sample and test stack "Hurley's Pencil"
The stack contains two images that can be reset after applying the
pencil graphics (and it repeats most of the text of this post) and a
radio-button group to change the paintcompression.
There are now three different graphics to be dragged around on the images:
The red graphic contains a modified version of your original script,
changing 4 pixels at once instead of 1 pixel on mousemove and using a
variable "movedobject" instead of the name of the graphic to start and
The yellow graphic contains an alternative script using a somewhat
different approach based on my own basic format for the handling of
imagedata. It enables you also to easily change the number of pixels
involved when dragging the graphic.
In the script of the green graphic
line "set the imagedata of img "mine2" to idata"
has been moved from the "mousemove" handler to the mouseup "handler",
causing the image to be redrawn only after the moved graphic has been
There are at least two basic problems for imagedata manipulation:
1. Processing imagedata with RLE paintcompression is up to 12 times
faster than with PNG (in extreme cases).
See Bugzilla 5113 and the accompanying test stack
Contrary to the Metacard IDE, Revolution sets the paintcompression to
PNG on startup. If you use Revolution, set the paintcompression to RLE
to speed up all imagedata processes. You can test the speed differences
by changing the paintcompression with the radio buttons at the top of
the sample stack.
2. You can get and set the imagedata only for a whole image via a
variable. You cannot access and change individual or a range of pixels
"put numtochar(100) into char 2500 of the imagedata of image "x"".
This means that although by moving the pencil graphic only a few pixels
are changed, each time the graphic is moved the entire imagedata is
being set anew (when using the red and yellow graphics).
This also means that the larger the image the slower the possible
movement of the pencil graphic will be. I tested this on an image
2048X1536 where the pencil graphic could be hardly moved even with the
paintcompression set to RLE.
Hopefully we will get such an enhancement to directly set the color of
individual pixels in images in the future.
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