PNG with No Alpha Channel?

Luis luis at anachreon.co.uk
Wed Jun 11 08:50:38 CDT 2008


Ok, if you look at a 32 bit png in ascii near the start of the file  
then you'll spot the bKGD chunk, this defines the background and it  
looks like it also contains the alpha value. On a 24 bit png (no  
alpha) this value is not present...
The bKGD chunk may not be honoured in all viewers.
I don't know how this change may reflect on the final image but it  
might be worth a shot!

Cheers,

Luis.


On 11 Jun 2008, at 13:56, Luis wrote:

> The export snapshot creates a 32 bit png if the image has an alpha  
> channel, so it's grabbing the 'display' at 32 bits.
> I'm wondering if changing the colour depth to 24 bit the snapshot  
> will generate a 24 bit png, without the alpha channel.
>
> Cheers,
>
> Luis.
>
>
>
> On 11 Jun 2008, at 13:14, Trevor DeVore wrote:
>
>> On Jun 11, 2008, at 6:33 AM, Luis wrote:
>>
>>> What are you creating the png images with? I recall seeing  
>>> different save options for png in The Gimp, can't recall them  
>>> exactly now (I think you could strip out the gamma and the  
>>> background from the save as well as setting the interlace).
>>
>> I'm creating the PNG images in Revolution using export snapshot  
>> and then using the images in PDF documents created using Jan's  
>> library. This is part of an existing end-user application rather  
>> than some sort of workflow I'm trying to create for myself which  
>> is why I was in search of a Revolution only solution rather than  
>> compiling additional libraries that I would have to include for  
>> this one task.
>>
>> In regards to your question about exporting to GIF and then  
>> converting to PNG -
>>
>> GIF doesn't have enough colors but even if it did you would still  
>> be back to the original question of how to create a PNG in  
>> Revolution with no alpha channel.
>>
>> Regards,
>>
>> -- 
>> Trevor DeVore
>> Blue Mango Learning Systems
>> www.bluemangolearning.com    -    www.screensteps.com
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