Re: Atkinson dither algorithm

[Tom Glod via use-livecode]

wow! my brain hurts.

On Tue, Oct 17, 2017 at 2:13 PM, Alejandro Tejada via use-livecode <
use-livecode@lists.runrev.com> wrote:

> Hermann, your script version won the
> LiveCode Script speed contest! :-)
>
> I feel humbled and grateful that many of you
> have taken time to look at this. Although an
> image dithering algorithm seems trivial an
> barely useful, the fact is that in this thread,
> we have pushed Livecode script almost to
> it's speed limits.
>
> After we reach Livecode scripts natural limits,
> the next step is
> 1) creating a command line application, or
> 2) building an external, or (like Hermann demonstrated)
> 3) using Javascript within the browser widget or
> 4) the next frontier: Livecode widgets.
>
> This platform does not lack options to get the job
> done. It just require time and expertise to select
> the best options for each phase of a particular project.
>
> Later today, after I finished testing an application in
> different computers, will update the forum final's
> stack version with Alex and Hermann scripts.
>
> Thanks a lot again! :-D
>
> Al
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Re: Atkinson dither algorithm

[Alejandro Tejada via use-livecode]

Hermann, your script version won the
LiveCode Script speed contest! :-)

I feel humbled and grateful that many of you
have taken time to look at this. Although an
image dithering algorithm seems trivial an
barely useful, the fact is that in this thread,
we have pushed Livecode script almost to
it's speed limits.

After we reach Livecode scripts natural limits,
the next step is
1) creating a command line application, or
2) building an external, or (like Hermann demonstrated)
3) using Javascript within the browser widget or
4) the next frontier: Livecode widgets.

This platform does not lack options to get the job
done. It just require time and expertise to select
the best options for each phase of a particular project.

Later today, after I finished testing an application in
different computers, will update the forum final's
stack version with Alex and Hermann scripts.

Thanks a lot again! :-D

Al
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Re: Atkinson dither algorithm

[hh via use-livecode]

@Alejandro and Alex.

All that limit checking is not needed here. It is much faster,
especially for fast images,to do a few unneeded additions than
to do all these checks for each pixel.

I translated my js-function into LC Script, using Alejandro's
variable names and (inline) Alex's array creation method. See
http://forums.livecode.com/viewtopic.php?p=159244#p159244

You certainly can improve this LCS script even more. In javascript
this is so fast that even for large images there is no gain by
'optimization'.

p.s. Al, you don't need a "try". Just use (where 3 = step-1)
repeat with i = 1 to the number of bytes in tempVar - 3 step 4


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Re: Atkinson dither algorithm

[Alejandro Tejada via use-livecode]

Hi Alex,

This is Amazing! :-D
Alex, your function saved another 34%
in the running time of this handler!

In retrospect, only now it seems very obvious
that merging two functions could save more
running time in this handler... but
I just keep wondering: How far can we go
merging functions to save milliseconds
in our LiveCode handlers? This is an interesting
question that could be answered exactly
in milliseconds.

By the way, I have to add a try structure to dismiss
an error message:

Function ImgToChToArrayNum2 tImageData, tChannel
-- extract a single channel's data, and convert
-- to sequential array of numbers by Alex Tweedly

put tImageData into tempVar
delete byte 1 to tChannel of tempVar
put empty into tResult
put 0 into tCounter
repeat with i = 1 to the number of bytes in tempVar step 4
   add 1 to tCounter
   try
  put bytetonum(byte i of tempVar) into tResult[tCounter]
  end try
end repeat
return tResult
end ImgTochToArrayNum2

Alex Tweedly wrote:
> I haven't tackled the second half (i.e. the actual dithering bit yet -
> maybe tomorrow).

Excellent! Thanks a lot for your time, Alex.

Al
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Re: Atkinson dither algorithm

[Alex Tweedly via use-livecode]

On 17/10/2017 00:21, Alex Tweedly via use-livecode wrote:

Sorry about the horrible formatting on the last post... I'll try to find 
my Forum password and post the modified version there 


I haven't tackled the second half (i.e. the actual dithering bit yet - 
maybe tomorrow).

I can trim a few ms off this, but it's really not significant.

Change the checks for being near the right hand side of the image from 
'if's to a switch.


Then,  after you've calculated and used tNewKey, change following lines 
like :


*if* tPixelPosition modtImageWidth <> 1*then**
    put (tPixelPosition + tImageWidth - 1) into tNewKey**
   add*(tDifusionError) totArray2[tNewKey]*
end* *if*


to


*if* tPixelPosition modtImageWidth <> 1*then**
    add*(tDifusionError) totArray2[tNewKey-1]*
end* *if*


but it really is nit-picking - only a tine saving.

-- Alex.

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Re: Atkinson dither algorithm

[Alex Tweedly via use-livecode]

On 16/10/2017 19:37, Alejandro Tejada via use-livecode wrote:

Hi Bob,

Bob Sneidar wrote:

I didn't post any code I don't think, but I will certainly
take some credit for having done so! ;-)

In fact, you are not late! :-D

But I am too late - the file is called "...Final Version ..." :-) :-)
Let's have a look anyway

Please, take a look at the script of
Atkinson Dither 04 (Fastest Version)
and make it faster.

OK, did that :-)

I've been aware of this interesting discussion, but had no time to look 
at it at all (until tonight). Sorry to be late to the party.


I made a few changes, as follows:

1. (Just on principle).
I would change all these reference to "char" to "byte" when we are 
really talking about bytes in binary data.


Probably doesn't make any difference to performance - the engine will 
most likely realize that there aren't any Unicode strings involved - but 
it's just "right" to call them bytes, and to use the byte functions to 
manipulate them :-)


2. there's a function ImgToCh which extracts a single channel of data 
out the image data.
It does this with a cute 'delete' method - but that is over-thinking the 
problem.
You can (i.e. the engine can) access a single byte within a byte string 
in constant time (it's surely a single offset in the C library).


so instead of


repeat untiltempVar isempty
  putchar1oftempVar aftertResult
  deletechar1to4oftempVar
end repeat


we can simply do


*repeat* withi = 1tothenumberofcharsintempVar step4*
  put*bytei oftempVar aftertemp*
end* *repeat*

(I kept the initial delete to select which channel, just because it's so 
clever :-) - but that could have been removed and the repeat changed to

*   repeat* withi = tChannel+1tothenumberofcharsintempVar step4*
*

3. The result of that function is then passed to another function that 
converts the byte string into a sequential array of numbers (and that's 
all that's done with the byte string).

So those two should be combined into a single pass - to get :


Function ImgToChToArrayNum2 tImageData, tChannel
   -- extract a single channel's data, and convert to sequential array 
of numbers

   puttImageData intotempVar
   deletebyte1totChannel oftempVar
   putemptyintotResult
put0intotCounter
   repeat withi = 1tothenumberofbytesintempVar step4
  add1totCounter
  putbytetonum(bytei oftempVar) intotResult[tCounter]
   end repeat
   returntResult
end ImgTochToArrayNum2

This takes the time for this part of the whole process down from 250ms 
to about 75ms, and therefore the total process time down from around 
750-800ms to 600-650ms (on my aging MBP).


Trying repeated runs, the times do seem to vary more than usual - not 
sure why.


I haven't tackled the second half (i.e. the actual dithering bit yet - 
maybe tomorrow).


-- Alex.

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Re: Atkinson dither algorithm

[Bob Sneidar via use-livecode]

I didn't post any code I don't think, but I will certainly take some credit for 
having done so! ;-)

Bob S


> On Oct 14, 2017, at 21:57 , Alejandro Tejada via use-livecode 
>  wrote:
> 
> Hi All,
> 
> This forum message contains the final version of this stack.
> It includes a Color version of this algorithm.
> 
> https://forums.livecode.com/viewtopic.php?f=10=159173#p159173
> 
> Thanks again to Malte Brill, Richard Gaskin, Hermann Hoch, Mark Waddingham,
> Peter Reid, Ben Rubinstein, Bob Sneidar and Lagi Pittas for posting scripts
> and
> writing ideas to improve this handler.
> 
> Al


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Re: Atkinson dither algorithm

[Alejandro Tejada via use-livecode]

Hi All,

This forum message contains the final version of this stack.
It includes a Color version of this algorithm.

https://forums.livecode.com/viewtopic.php?f=10=159173#p159173

Thanks again to Malte Brill, Richard Gaskin, Hermann Hoch, Mark Waddingham,
Peter Reid, Ben Rubinstein, Bob Sneidar and Lagi Pittas for posting scripts
and
writing ideas to improve this handler.

Al
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Re: Atkinson dither algorithm & 'for each' loop

[Lagi Pittas via use-livecode]

HI All

Hoping I'm not teaching my granny to suck eggs ... Here is a great article
I remembered reading  from a few years ago. It's easy to find on google so
you probably know of it ...

http://www.tannerhelland.com/4660/dithering-eleven-algorithms-source-code/

In any case his projects and how he writes about them are interesting

 http://www.tannerhelland.com/programming-directory/

Lagi

On 12 October 2017 at 12:05, Peter Reid via use-livecode <
use-livecode@lists.runrev.com> wrote:

> One note of caution regarding the use of the "repeat for each" loop,
> whilst you will get a loop iteration for every value in the collection
> (fldhexa3 in your example), you are not guaranteed the order in which they
> will occur.  This doesn't matter in a lot of cases but does matter when the
> sequence is significant.  In the case of your example I believe sequence is
> critical, otherwise the pixels might appear to be scrambled!
>
> The following adjusted loop guarantees the sequence at the expense of
> speed:
>
>   put 1 into i
>   repeat for each word theWord in fldhexa3
>  put word i of fldhexa3 into theWord
>  put 00 & theword & theword & theword after tVar2
>  add 1 to i
>   end repeat
>
> The original "improved" loop reduces the run-time to 25%.  However, the
> "modified improved" loop only manages to reduce the original run-time to
> 50%.
>
> The suggested loop above takes advantage of the "for each" mechanism to
> produce a set of iterations very rapidly but gets slowed by the need to
> guarantee sequence. I wonder whether the LC engine could impose strict
> sequence more effectively with a variant of the "for each" loop such as
>
>   repeat for each sequenced word x in theCollection
>  ...
>   end repeat
>
> My own tests, comparing the speed of the 4 common repeat loops, imply that
> the current "for each" form is hugely faster than the others.  I tested
> "repeat for each...", "repeat while...", "repeat until...", "repeat
> with..." and a simulated "repeat for each sequenced..." forms using a
> simple loop body that added lines of text one after another, e.g.
>
>   put empty into tData
>   repeat with i = 1 to tMaxI
> put line i of tList & return after tData
>   end repeat
>
> I ran this test for 250,000 iterations for each type of loop, which
> produced the following timings:
>
>   Starting test for 250,000 iterations...
>   repeat for each... 0 mins 0 secs 111 millisecs
>   repeat while... 0 mins 30 secs 569 millisecs
>   repeat until... 0 mins 30 secs 379 millisecs
>   repeat with... 0 mins 30 secs 341 millisecs
>   repeat for each seq... 0 mins 30 secs 524 millisecs
>
> As you can see, in this test the "repeat for each..." form was approx. 275
> times faster than the other forms.  Also the simulated "repeat for each
> sequenced..." form was no faster than the other forms.  This shows how
> variable the speed will be with the simulated "repeat for each
> sequenced...", depending on the details of the loop body.
>
> If there was a "repeat for each sequenced..." form of loop in LC, any
> speed-up could be very beneficial even if the amount of speed-up was only
> 10 times faster!
>
> Cheers
>
> Peter
> --
> Peter Reid
> Loughborough, UK
>
> > On 9 Oct 2017, at 10:18am, use-livecode-requ...@lists.runrev.com wrote:
> >
> > Message: 12
> > Date: Sat, 7 Oct 2017 15:53:44 +0200
> > From: Malte Pfaff-Brill <revolut...@derbrill.de>
> > To: use-livecode@lists.runrev.com
> > Subject: Re: Atkinson dither algorithm
> > Message-ID: <42023b36-0a4e-4251-bb0c-9cd46de55...@derbrill.de>
> > Content-Type: text/plain; charset=us-ascii
> >
> > Hi Al,
> >
> > I already posted on the forums, but for completeness also here:
> >
> > a lot can be done by replacing repeat with with repeat for each where
> you can.
> >
> > --repeat with i = 1 to the number of words of fldhexa3
> >   --   put 00 & word i of fldhexa3 & word i of fldhexa3 & word i of
> fldhexa3 after tVar2
> >   --end repeat
> >
> >   repeat for each word theWord in fldhexa3
> >  put 00 & theword & theword & theword after tVar2
> >   end repeat
> >
> >
> > A sidenode:
> >
> > I always use strict compile mode, therefore I added the needed variable
> declarations and noticed you use startTime as a variablename, which is a
> reserved keyword. That is not a good idea.  (I noticed, because I managed
> to freeze liveCode where I fixed only half of the use of startTime. Booom.)
> >
> > Cheers,
> >
> > malte
>
>
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Re: Atkinson dither algorithm & 'for each' loop

[hh via use-livecode]

@Al.
For multiples of 1/8 (Atkinson) you need 8*256=2048 integers,
that is 11 Bit.
For multiples of 1/16 (Floyd-Steinberg) you need 16*256=4096
integers, that is 12 Bit.
In 2 chars = 16 Bit fit even multiples of 1/256.
No dither-algorithm uses such tiny diffusion-errors.

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Re: Atkinson dither algorithm & 'for each' loop

[hh via use-livecode]

> Al wrote:
> Please, check this new handler in the forum and suggest how to
> make this faster and more precise.

I already gave you a method that is, with a 500x500 image, at
least 1000 (thousand) times faster than your script.

Of course this is not due my special skills but the ability of
javascript (used via a browser widget) to let the GPU/graphic
card do the essential job of pixel manipulation.

So all considerations to improve the LCS script are, TMHO, of
rather theoretical value. Here are some more:

> Al wrote:
> ... the result STILL is not visually identical to that handler.
> My educated guess is that Atkinson dither algorithm requires
> numbers with more than 2 numbers after the decimal point.
> That is: 243.643578 instead of just 243.64

Conclude from the following:
The Atkinson algorithm uses multiples of 1/8 = 0.125 for the
diffusion-error, the Floyd-Steinberg algorithm uses multiples
of 1/16 = 0.0625. 

And have this in mind:
Whenever you use numToChar(Number) in your script you are wrong by
Number - round(Number) of the accumulated pixel value ...

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Re: Atkinson dither algorithm & 'for each' loop

[Mark Waddingham via use-livecode]

On 2017-10-12 19:35, Alejandro Tejada via use-livecode wrote:

Peter Read wrote:

One note of caution regarding the use of the "repeat for each" loop,
whilst you will get a loop iteration for every value in the collection
(fldhexa3 in your example), you are not guaranteed the order in
which they will occur. This doesn't matter in a lot of cases but
does matter when the sequence is significant.  In the case of your
example I believe sequence is critical, otherwise the pixels might
appear to be scrambled!


Prior to 7, you had to be careful not to modify either the container 
being iterated over *or* the var holding the chunk for the current 
iteration as it could cause issues as described (actually, it was 
fundamentally unsafe to do that, as it could result in a crash). i.e.


  repeat for each item tItem in tContainer
replace "Foo" with "B" in tContainer -- BAD - MIGHT CAUSE PROBLEMS
put "a' into char 2 of tItem -- BAD - MIGHT CAUSE PROBLEMS
  end repeat

From 7 onwards, this is no longer the case. You can do whatever you want 
with either the container. Indeed, in 7, the engine essentially operates 
as if it was iterating over a copy of the container and with a copy of 
the chunk (i.e. tItem and tContainer in the above snippet).


Upshot - you can do whatever you want with your variables - the engine 
ensures that what you do won't affect what you asked for to begin with 
(in particular, if you asked to iterate over tContainer, then it will 
iterate over tContainer as it was at the point you first asked - any 
changes to tContainer after the initial repeat for each line will have 
no effect on the repeat for each clause).


Warmest Regards,

Mark.

--
Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps

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Re: Atkinson dither algorithm & 'for each' loop

[Richard Gaskin via use-livecode]

Peter Reid wrote:

> One note of caution regarding the use of the "repeat for each" loop,
> whilst you will get a loop iteration for every value in the collection
> (fldhexa3 in your example), you are not guaranteed the order in which
> they will occur.

Maybe I misunderstand, but are you thinking of arrays there?

With string containers a "repeat for each" expression should parse from 
beginning to end, sequentially.


Any exception to that would be prohibitively unpredictable, and should 
be reported as a bug.



> The following adjusted loop guarantees the sequence at the expense of
> speed:
>
>   put 1 into i
>   repeat for each word theWord in fldhexa3
>  put word i of fldhexa3 into theWord

The speed lost there appears to be the result of a redundancy, and a 
particularly expensive one:


We love the convenience of chunk expressions, but in loops we want to 
remain mindful of "  of " because satisfying 
such expressions will require the engine to start from the beginning of 
the container, examine every character and counting delimiters, until it 
reaches the number of such delimiters specified in "".


So the "repeat" line above parses the chunk value into theWord, but then 
the next line ignores that that's already happened and reassigns the 
same theWord value using an expression that requires then engine to 
count words from the beginning of fldhexa3 each time through the loop.



With this specific algo I believe there may be further benefits in using 
a chunk type other than word (based on a a hunch derived from word 
chunks being parsed more flexibly than items or lines), and perhaps not 
converting the binary data to hex at all, instead parsing bytes directly 
with a "step 4" option in the loop to keep track of the four components 
that define each pixel.


--
 Richard Gaskin
 Fourth World Systems
 Software Design and Development for the Desktop, Mobile, and the Web
 
 ambassa...@fourthworld.comhttp://www.FourthWorld.com

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Re: Atkinson dither algorithm & 'for each' loop

[Bob Sneidar via use-livecode]

That is correct Ben. It's not the repeat for each that is unreliable (probably 
a bad word to use here) but it is arrays which do not retain the sequence of 
key/values in the order they were put in. 

To get around this, when possible use numbered keys, then:

put  the keys of aMyArray into tKeyList
sort the lines of tKeyList numeric ascending
repeat for each line tKey in tKeyList
...

Bob S


> On Oct 12, 2017, at 04:48 , Ben Rubinstein via use-livecode 
>  wrote:
> 
> Hi Peter,
> 
>> One note of caution regarding the use of the "repeat for each" loop, whilst 
>> you will get a loop iteration for every value in the collection
>> (fldhexa3 in your example), you are not guaranteed the order in which they
>> will occur.
> 
> Are you sure? My understanding has always been that chunk items, e.g.
>   repeat for each [ byte | char | word | item | line]  in 
> 
> will always be sequential (indeed that's why this structure is fast) - it's 
> only when dealing with hashed arrays that the sequence is not reliable, i.e.
>   repeat for each key  in 
>   repeat for each element  in 
> 
> Do you have experience to the contrary?
> 
> best regards,
> 
> Ben


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Re: Atkinson dither algorithm & 'for each' loop

[Ben Rubinstein via use-livecode]

Hi Peter,

One note of caution regarding the use of the "repeat for each" loop, 
whilst you will get a loop iteration for every value in the collection

(fldhexa3 in your example), you are not guaranteed the order in which they
will occur.


Are you sure? My understanding has always been that chunk items, e.g.
repeat for each [ byte | char | word | item | line]  in 

will always be sequential (indeed that's why this structure is fast) - it's 
only when dealing with hashed arrays that the sequence is not reliable, i.e.

repeat for each key  in 
repeat for each element  in 

Do you have experience to the contrary?

best regards,

Ben

On 12/10/2017 12:05, Peter Reid via use-livecode wrote:

One note of caution regarding the use of the "repeat for each" loop, whilst you 
will get a loop iteration for every value in the collection (fldhexa3 in your example), 
you are not guaranteed the order in which they will occur.  This doesn't matter in a lot 
of cases but does matter when the sequence is significant.  In the case of your example I 
believe sequence is critical, otherwise the pixels might appear to be scrambled!

The following adjusted loop guarantees the sequence at the expense of speed:

   put 1 into i
   repeat for each word theWord in fldhexa3
  put word i of fldhexa3 into theWord
  put 00 & theword & theword & theword after tVar2
  add 1 to i
   end repeat

The original "improved" loop reduces the run-time to 25%.  However, the "modified 
improved" loop only manages to reduce the original run-time to 50%.

The suggested loop above takes advantage of the "for each" mechanism to produce a set of 
iterations very rapidly but gets slowed by the need to guarantee sequence. I wonder whether the LC 
engine could impose strict sequence more effectively with a variant of the "for each" 
loop such as

   repeat for each sequenced word x in theCollection
  ...
   end repeat

My own tests, comparing the speed of the 4 common repeat loops, imply that the current "for each" form is hugely faster than the 
others.  I tested "repeat for each...", "repeat while...", "repeat until...", "repeat with..." and 
a simulated "repeat for each sequenced..." forms using a simple loop body that added lines of text one after another, e.g.

   put empty into tData
   repeat with i = 1 to tMaxI
 put line i of tList & return after tData
   end repeat

I ran this test for 250,000 iterations for each type of loop, which produced 
the following timings:

   Starting test for 250,000 iterations...
   repeat for each... 0 mins 0 secs 111 millisecs
   repeat while... 0 mins 30 secs 569 millisecs
   repeat until... 0 mins 30 secs 379 millisecs
   repeat with... 0 mins 30 secs 341 millisecs
   repeat for each seq... 0 mins 30 secs 524 millisecs

As you can see, in this test the "repeat for each..." form was approx. 275 times faster than the 
other forms.  Also the simulated "repeat for each sequenced..." form was no faster than the other 
forms.  This shows how variable the speed will be with the simulated "repeat for each 
sequenced...", depending on the details of the loop body.

If there was a "repeat for each sequenced..." form of loop in LC, any speed-up 
could be very beneficial even if the amount of speed-up was only 10 times faster!

Cheers

Peter
--
Peter Reid
Loughborough, UK


On 9 Oct 2017, at 10:18am, use-livecode-requ...@lists.runrev.com wrote:

Message: 12
Date: Sat, 7 Oct 2017 15:53:44 +0200
From: Malte Pfaff-Brill <revolut...@derbrill.de>
To: use-livecode@lists.runrev.com
Subject: Re: Atkinson dither algorithm
Message-ID: <42023b36-0a4e-4251-bb0c-9cd46de55...@derbrill.de>
Content-Type: text/plain; charset=us-ascii

Hi Al,

I already posted on the forums, but for completeness also here:

a lot can be done by replacing repeat with with repeat for each where you can.

--repeat with i = 1 to the number of words of fldhexa3
   --   put 00 & word i of fldhexa3 & word i of fldhexa3 & word i of 
fldhexa3 after tVar2
   --end repeat

   repeat for each word theWord in fldhexa3
  put 00 & theword & theword & theword after tVar2
   end repeat


A sidenode:

I always use strict compile mode, therefore I added the needed variable 
declarations and noticed you use startTime as a variablename, which is a 
reserved keyword. That is not a good idea.  (I noticed, because I managed to 
freeze liveCode where I fixed only half of the use of startTime. Booom.)

Cheers,

malte



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Re: Atkinson dither algorithm & 'for each' loop

[Peter Reid via use-livecode]

One note of caution regarding the use of the "repeat for each" loop, whilst you 
will get a loop iteration for every value in the collection (fldhexa3 in your 
example), you are not guaranteed the order in which they will occur.  This 
doesn't matter in a lot of cases but does matter when the sequence is 
significant.  In the case of your example I believe sequence is critical, 
otherwise the pixels might appear to be scrambled!

The following adjusted loop guarantees the sequence at the expense of speed:

  put 1 into i
  repeat for each word theWord in fldhexa3
 put word i of fldhexa3 into theWord
 put 00 & theword & theword & theword after tVar2
 add 1 to i
  end repeat

The original "improved" loop reduces the run-time to 25%.  However, the 
"modified improved" loop only manages to reduce the original run-time to 50%.

The suggested loop above takes advantage of the "for each" mechanism to produce 
a set of iterations very rapidly but gets slowed by the need to guarantee 
sequence. I wonder whether the LC engine could impose strict sequence more 
effectively with a variant of the "for each" loop such as

  repeat for each sequenced word x in theCollection
 ...
  end repeat

My own tests, comparing the speed of the 4 common repeat loops, imply that the 
current "for each" form is hugely faster than the others.  I tested "repeat for 
each...", "repeat while...", "repeat until...", "repeat with..." and a 
simulated "repeat for each sequenced..." forms using a simple loop body that 
added lines of text one after another, e.g.

  put empty into tData
  repeat with i = 1 to tMaxI
put line i of tList & return after tData
  end repeat

I ran this test for 250,000 iterations for each type of loop, which produced 
the following timings:

  Starting test for 250,000 iterations...
  repeat for each... 0 mins 0 secs 111 millisecs
  repeat while... 0 mins 30 secs 569 millisecs
  repeat until... 0 mins 30 secs 379 millisecs
  repeat with... 0 mins 30 secs 341 millisecs
  repeat for each seq... 0 mins 30 secs 524 millisecs

As you can see, in this test the "repeat for each..." form was approx. 275 
times faster than the other forms.  Also the simulated "repeat for each 
sequenced..." form was no faster than the other forms.  This shows how variable 
the speed will be with the simulated "repeat for each sequenced...", depending 
on the details of the loop body.

If there was a "repeat for each sequenced..." form of loop in LC, any speed-up 
could be very beneficial even if the amount of speed-up was only 10 times 
faster!

Cheers

Peter
--
Peter Reid
Loughborough, UK

> On 9 Oct 2017, at 10:18am, use-livecode-requ...@lists.runrev.com wrote:
> 
> Message: 12
> Date: Sat, 7 Oct 2017 15:53:44 +0200
> From: Malte Pfaff-Brill <revolut...@derbrill.de>
> To: use-livecode@lists.runrev.com
> Subject: Re: Atkinson dither algorithm  
> Message-ID: <42023b36-0a4e-4251-bb0c-9cd46de55...@derbrill.de>
> Content-Type: text/plain; charset=us-ascii
> 
> Hi Al,
> 
> I already posted on the forums, but for completeness also here:
> 
> a lot can be done by replacing repeat with with repeat for each where you can.
> 
> --repeat with i = 1 to the number of words of fldhexa3
>   --   put 00 & word i of fldhexa3 & word i of fldhexa3 & word i of 
> fldhexa3 after tVar2
>   --end repeat
> 
>   repeat for each word theWord in fldhexa3
>  put 00 & theword & theword & theword after tVar2
>   end repeat
> 
> 
> A sidenode:
> 
> I always use strict compile mode, therefore I added the needed variable 
> declarations and noticed you use startTime as a variablename, which is a 
> reserved keyword. That is not a good idea.  (I noticed, because I managed to 
> freeze liveCode where I fixed only half of the use of startTime. Booom.)
> 
> Cheers,
> 
> malte


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Re: Atkinson dither algorithm

[Alejandro Tejada via use-livecode]

Hi Malte,

Malte Brill wrote:
> I already posted on the forums, but for completeness also here:
> a lot can be done by replacing repeat with with repeat for each where you
can.
>
> --repeat with i = 1 to the number of words of fldhexa3
> --put 00 & word i of fldhexa3 & word i of fldhexa3 & word i of
fldhexa3 after tVar2
> --end repeat
>
> repeat for each word theWord in fldhexa3
>  put 00 & theword & theword & theword after tVar2
> end repeat

This change reduced the time in a 25%!
Wonderful. Thanks a lot Malte :-D

> I always use strict compile mode, therefore I added the needed variable
> declarations and noticed you use startTime as a variablename, which is a
> reserved keyword. That is not a good idea.  (I noticed, because I managed
to
> freeze liveCode where I fixed only half of the use of startTime. Booom.)

startTime is a property of media players, so I am surprised that
LiveCode do not warn me about this. :-o

Also, I will try others less complex and simpler dithering algorithms as
Floyd-Steinberg and Sierra Lite to measure total time differences.

http://www.tannerhelland.com/4660/dithering-eleven-algorithms-source-code/

Malte, Thanks again for taking a look and improve this code!
Have a nice weekend!

Al
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Re: Atkinson dither algorithm

[Malte Pfaff-Brill via use-livecode]

Hi Al,

I already posted on the forums, but for completeness also here:

a lot can be done by replacing repeat with with repeat for each where you can.

 --repeat with i = 1 to the number of words of fldhexa3
   --   put 00 & word i of fldhexa3 & word i of fldhexa3 & word i of 
fldhexa3 after tVar2
   --end repeat

   repeat for each word theWord in fldhexa3
  put 00 & theword & theword & theword after tVar2
   end repeat


A sidenode:

I always use strict compile mode, therefore I added the needed variable 
declarations and noticed you use startTime as a variablename, which is a 
reserved keyword. That is not a good idea.  (I noticed, because I managed to 
freeze liveCode where I fixed only half of the use of startTime. Booom.)

Cheers,

malte
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Re: Atkinson dither algorithm

[Alejandro Tejada via use-livecode]

I have posted a demo stack in the forums:
https://forums.livecode.com/viewtopic.php?f=10=29935

Have a nice weekend!
Al

On Sat, Oct 7, 2017 at 1:52 AM, Alejandro Tejada 
wrote:

> Hi All,
>
> I am stuck trying to make this code for Bill Atkinson
> dithering algorithm much more faster.
> Any ways to speed this code?
> Follow the recipe and watch out for lines broken
> by mail character length limit.
>
> Recipe:
>
> 1) Import an small image (200x200 pixels) and
> name it as "Image" (you could import a small
> transparent png or a small jpg image)
>
> 2) Optionally, create a scrollbar type slider
> with a range between 0 and 255.
> Set the name of this scrollbar as "ThresholdDither"
> and move the slider to 127 or 0 or 255.
>
> 3) Paste the following script in a button and
> click on it to run this code:
>
> on mouseUp
>
>put the millisecs into startTime
>set the cursor to busy
>
>put the alphadata of img "Image" into tAlphaData
>put the imagedata of img "Image" into tVar
>-- img "Image" could be a grayscale image
>-- where all 3 channels: Red, Green, Blue
>-- are identical or a color image where only
>-- the red channel is used
>
>delete char 1 of tVar
>-- the first char of the imagedata is part
>-- of the alphadata or maskdata
>repeat with i = 1 to length(tVar) step 4
>   put chartonum(char i of tVar) & space after fldhex
>end repeat
>delete last char of fldhex -- a space
>-- fldhex now contains a single channel of the RGB image
>-- converted to numbers between 0 and 255
>
>put the number of words of fldhex into lenghtofldhex
>put the width of img "Image" into tImageWidth
>put the height of img "Image" into tImageHeight
>
>repeat with i = 1 to lenghtofldhex step tImageWidth
>-- We need as many words per line, as pixels contains
>-- the image width (because each pixel is represented
>-- by a word and this word is number between 0 and 255)
>
>put word i to ( i + ((tImageWidth) - 1)) of fldhex & cr after fldhexa2
>end repeat
>
>put empty into fldhex
>delete last char of fldhexa2
>-- deleting the last cr character
>
>put the number of lines of fldhexa2 into sYsize
>put the number of words of line 1 of fldhexa2 into sXsize
>
>// get the scrollbar value
>-- tThreshold is a value between 0 and 255
>if existence(sb the "ThresholdDither") then
>put thumbPos of sb the "ThresholdDither" into tThreshold
>else
>put 127 into tThreshold
>end if
>
>repeat with tY = 1 to sYsize
>   repeat with tX = 1 to sXsize
>
>  put tX into tPixelPosition
>
>  put word (tPixelPosition) of line tY of fldhexa2 into
> tOldPixelValue
>
>  if round(tOldPixelValue) <= tThreshold then
> put 0 into tNewPixelValue
>  else
> put 255 into tNewPixelValue
>  end if
>
>  put (tOldPixelValue - tNewPixelValue)/8 into tDifusionError
>
>  -- Atkinson dither add the diffusion error
>  -- to 6 adjacent pixels
>  -- x o o
>  --  o o o
>  -- o
>
>  put tNewPixelValue & space after fldhexa3
>
>
> if tPixelPosition < sXsize then
>put tDifusionError + word (tPixelPosition + 1) of line tY
> of fldhexa2 into word (tPixelPosition + 1) of line tY of fldhexa2
>
>
>   if tPixelPosition < (sXsize-1) then
>   put tDifusionError + word (tPixelPosition + 2) of line
> tY of fldhexa2 into word (tPixelPosition + 2) of line tY of fldhexa2
>end if
>
>
> end if
>
>
> if tY < sYsize then
>
>
>if tPixelPosition > 1 then
>   put tDifusionError + word (tPixelPosition - 1) of line
> tY + 1 of fldhexa2 into word (tPixelPosition - 1) of line tY + 1 of fldhexa2
>end if
>
>
>put tDifusionError + word (tPixelPosition) of line tY + 1
> of fldhexa2 into word (tPixelPosition) of line tY + 1 of fldhexa2
>
>
>if tPixelPosition < sXsize then
>   put tDifusionError + word (tPixelPosition + 1)  of line
> tY + 1 of fldhexa2 into word (tPixelPosition + 1) of line tY + 1 of fldhexa2
>end if
>
>
>if tY < (sYsize - 1) then
>   put tDifusionError + word (tPixelPosition) of line tY +
> 2 of fldhexa2 into word (tPixelPosition) of line tY + 2 of fldhexa2
>end if
>
>
> end if
>
>   end repeat
>end repeat
>
>replace "0" with "00" in fldhexa3
>replace "255" with "FF" in fldhexa3
>
>repeat with i = 1 to the number of words of fldhexa3
>   put 00 & word i of fldhexa3 & word i of fldhexa3 & word i of
> fldhexa3 after tVar2
>end repeat
>put binaryEncode("H*",tVar2) into tVar3
>
>create img
>set the height of it to the height of img "Image"
>set the width of it to the width of img