Ross Boylan wrote:
> On Tue, 2010-04-13 at 21:05 -0700, Andreas Raab wrote:
>   
>> Hi Ross -
>>
>> Profiling is your friend. In most cases, 95% of the time are spent in 5% 
>> of the code. From what you're saying below it sounds that you're using 
>> one of the 'special' PNG modes (black and white, or gray-scale) that 
>> probably have seen less attention for optimization than others. Any 
>> chance you can post a sample image for profiling it?
>>     
>
> I've attached a test image, which takes about 30 seconds for me.  It is
> a 1 bit depth image.  Not sure if the attachment will make it
> through....
>
> Ross
>   

Profiling is indeed your friend.
There is some serious inefficiency there. Quickly hacking this (warning: 
will only work for 1bpp):

copyPixelsGray: y
    "Handle non-interlaced grayscale color mode (colorType = 0)"
    | word base ii |
    base :=  y * form width//32 +1.
    0 to: thisScanline size-1 // 4 do: [ :i |
        ii := i * 4.
        word :=
            (thisScanline at: ii+1) << 24 bitOr: (
            (thisScanline at: ii+2) << 16 bitOr: (
            (thisScanline at: ii+3) << 8 bitOr: (
            (thisScanline at: ii+4)))).
        form bits at: base + i put: word ].

gives over 30x speed increase (from 10 seconds down to 310 mSec) on my 
system. This is not a solution, just some food for thought.

Cheers,
Juan Vuletich