World: r4wp

im1: as-byte 0

Well, that seems to have worked around the problem!  Thanks guys!

Now I can work on making some real progress! :-)

I'm amazed by how fast Red/System is.

Excellent !

Your code could be optimised a bit :-)

Kaj, I think there was something to the jarsigner being commented 
out in the file. I'll have to wait for Doc and Pekr to chime in.

Yes

I'd love to learn how to optimize my code!

Are you low on memory?

A simple one:

im1:  (as integer! r + g + b) / 3

That won't work

I meant :

im1: (as integer! r) + (as integer! g) + (as integer! b) / 3

2 additions & 1 division against 3 divisions & 2 additions

im1: (as-integer img1/r) + img1/g + img1/b / 3

But yes, that was my general idea

:-)

I now have a working rudimentary motion detection algorithm.  Now 
it's time to tune it with my special formula.

If you're not memory constrained, you can leave the / 3 out completely 
and compare two grayscales as integer values

Im1 is already an integer in Bo's code.

if you're desparate for a few millisecs, reversing the loop to start 
at the end and work toward the front will help.

(Subtraction being marginally faster then addiiton).

That could be cast to byte again, to save the grayscale, but yes, 
there's no need to divide by 3 if it's just for the comparison

I'm passing the processed image back out to Rebol to convert back 
into an image for visual verification of the motion detection algorithm. 
 That part works fine. :-)

Subtraction faster than addition? That would surprise me. It's comparison 
to 0 that may be faster

Further, the bumping of r, g and b each iteration is relatively much 
work, because you're also having to use them as indexes. It's more 
efficient to make a byte pointer for each and advance those

But it's probably even faster to iterate through the image with one 
integer pointer, because the pixels happen to be four bytes, and 
then use indexes of 2, 3 and 4 for r, g and b

So are you saying that if 'img1 is a pointer, to do the following?

	img1r: img1 + 2
	img1g: img1 + 3
	img1b: img1 + 4

and then

	img1r: img1r + 4
	img1g: img1g + 4
	img1b: img1b + 4

would be faster than what I'm doing now?

You're correct. I checked and the optimisation benefit through "loop 
inversion" apparently comes from reducing the number of jumps in 
the underlying code not difference in speed in atrithmetic.

OK, so this would be even faster:

r: 2
g: 3
b: 4
until [
	...do stuff here...
	img1: img1 + 4
	...comparison...
]

Bo, yes, that would be more efficient, because you can then index 
with 1

Bo, that's basically how it'd be done in C

Kaj do you know if Red/System generates the same code for :

	img1/value and img!/1 ?

Yes, it's equivalent

Thanks for the tips, guys!

There is no way for Red/System to read a directory listing, is there?

Perhaps fastest:
pixel: as int-ptr! img1 + 1
...
rgb: as-binary pixel
im1: (as-integer rgb/1) + rgb/2 + rgb/3 / 3
pixel: pixel + 1

That code would have to be tested, depends on lots of details

I'm only looping 20'000 times or so...not a lot for Red/System to 
handle. ;-)

But it's going to run on a Raspberry in realtime

I was joking. :-)

Can Red/System read a directory listing?

It should, but you have to interpret the data manually

I haven't looked into it yet

I see you'd need some extra definitions that aren't in my C library 
binding yet

james & kaj: I have JDK installed too, you should be sure, that you 
can call java, javac from whatever dir = it is in the system lookup 
PATH. And - Rebol was downloading supporting tools, then it hang 
in console, but in fact, there was a dialog box hidden in the background, 
asking me for write permission. Unless you allow that, the tools 
are not going to be saved into requested directory ...

My directory structure is:

build\tools:

\api\android.jar
jli.dll
aapt.exe
keytool.exe
zipalign.exe

@james_nak, first delete any jarsigner exe you might have downloaded 
or copied outside of the java folders. Then try to run jarsigner 
from the Red folder, if it says it can't be found, then you have 
to add to your PATH environment variable, the path to the java/bin/ 
folder of your installed JDK.

Doc - how do your slides go? :-) I hope you have prepared many questions 
for Carl :-)

Barely started, gone to see "Man of Steel" yesterday night to get 
some inspiration. ;-)