World: r4wp

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. ;-)

I'm trying to extend the build script for other platforms, but my 
Ubuntu 11.04 image somehow got stuck with old source repository versions 
and no way to install/update any packages...So I now need to install 
a 12.04 package in order to check the requirement for the build script 
and test it. I'm baffled that the support for a 2 years old Ubuntu 
version is so bad...

How was the movie? Seen trailer, liked it ...

I've found the trailer better than the movie, I was quite disappointed 
(I'm a huge DC comics fan)...the "epic" moments weren't that much 
epic to me, so the whole movie (2h30) was a bit borring...The Krypton 
civilisation and display technology were the most interesting parts 
to me. ;-) Actually, the movie reminded me a lot the "Tree of Life", 
like a mosaic of sequences, and with almost the same soporific audio 
track... No real breathtaking moments...Even the mandatory "love 
story" sounds fake... The fx +  3D was too much to me, you're quickly 
lost in the fight sequences. But that's just my opinion, others might 
like it very much. ;-)

If only Zack Snyder had chosen to adapt the "Red Son" instead...*that* 
would have been epic! ;-)

(Or "DC 1million" instead, with the original Superman coming out 
from the Sun core after 80k years of hibernation and meeting with 
the 843th Century's Superman with its incredibly enhanced abilities) 
;-)

11.04 is a non-LTS release, support officially ended Oct 2012.

For out-of-support distros, the package sources move to a different 
server.

Yes, I tried every 11.04 moved repo URL I could found online, none 
worked for me.

If you switch your apt sources to old-releases.ubuntu.com, things 
should work again.

Tried that, didn't work...

But I did it through Synaptic, I might try to do it manually...

deb http://old-releases.ubuntu.com/ubuntu/natty main restricted

(A correct entry for /etc/apt/sources.list, for reference.)