Exporting transparent PNGs (again)

[Jim Ault]

The key maybe the 
         repeat for each
which is a sequential access rather than
 'evaluate the access position each loop'

I also think that the larger the data source, the slower 'repeat with x ='
becomes.

Try these runs and see if the results are linear or exponential.

get ( number of chars in imagedata of image "A1"/4)
repeat with n = 1 to it/10
repeat with n = 1 to it/5
repeat with n = 1 to it/4
repeat with n = 1 to it/2
repeat with n = 1 to it/1


Jim Ault
Las Vegas

On 7/4/06 2:33 PM, "Chris Carroll-Davis" <asgg35 at dsl.pipex.com> wrote:

> Dave -
> 
> Thanks so much!  Yes, your routine is much faster than mine... though
> I'm not sure why!!
> 
> Here is my code:
> 
> on mouseUp
>    put alphadata of image "black" into temp
>    put the milliseconds into tStart ## for speed calc
>    repeat with n = 1 to number of chars in imagedata of image "A1"/4
>      put char n*4 of imagedata of image "A1" into char n of temp
>    end repeat
>    put the milliseconds - tStart && length(tMaskData) ##speed score
>    set alphadata of image "black" to temp
> end mouseUp
> 
> For some reason, even though my loop is only a quarter of the length
> of yours with just one line of code in it (and no decisions)  it is
> much slower.  It was slower still because I was (for daft reasons I
> wont go into!) originally doing the loop backwards.
> 
> I'll try to tweak to improve speed further, but even as it stands I
> think it should be fine.
> 
> Also, thanks Ken for the links.  They helped me understand what is
> going on now!
> 
> Regards,
> 
> Happy Chris
> 
> 
> On 4 Jul 2006, at 18:10, Dave Cragg wrote:
> 
>> 
>> I'm not sure what calculations you are doing in the loop, but it
>> sounds too slow. The following routine creates alphaData from a 300
>> x 300 grayscale image in less than a second on my not so fast
>> machine. (You'll probably need to substitute the calculation inside
>> the loop with your own.)
>> 
>> I'm sure others will step up with faster alternatives. :-)
>> 
>> 
>> on mouseUp
>> 
>>   put the imageData of image 1 into tImageData
>>   put the milliseconds into tStart ## for speed calc
>>   put 0 into tCount
>>   repeat for each char tChar in tImageData
>>     add 1 to tCount
>>     if tCount = 4 then
>>       put numToChar(255 - charToNum(tChar)) after tMaskData
>>       put 0 into tCount
>>     end if
>>   end repeat
>>   put the milliseconds - tStart && length(tMaskData) ##speed score
>>   set the alphaData of image 1 to tMaskData
>> end mouseUp
>> 
>> Cheers
>> Dave
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