Re: Reading RGBA pixel values from image on disk
Re: Reading RGBA pixel values from image on disk
- Subject: Re: Reading RGBA pixel values from image on disk
- From: John Joyce <email@hidden>
- Date: Fri, 11 Mar 2011 08:59:05 +0800
On Mar 11, 2011, at 6:46 AM, Paul M wrote:
>
> On 11/03/2011, at 8:00 AM, Kyle Sluder wrote:
>
>> On Thu, Mar 10, 2011 at 10:47 AM, Leonardo <email@hidden> wrote:
>>> I forgot: if I save the TIF from Photoshop marking the check-box "Save
>>> Transparency", on my App I can quite read the alpha channel, and the RGB
>>> values are not pre-multiplied. That's fine.
>>> Anyway, without the "Save Transparency", on my App I get the RGB values
>>> pre-multiplied and the alpha values are all 1.0, so I can't calculate the
>>> original RGB values. The weird point is that if I re-open this TIF file with
>>> Photoshop, the half-a-transparent pixels are well visible. So the alpha
>>> information has been properly stored within the TIF file, somewhere. I would
>>> like to know where.
>>
>> Probably in a custom Photoshop chunk.
>>
>> TIFF isn't a very well-standardized format. Photoshop sticks a ton of
>> stuff in custom chunks.
>
>
> The spec is here:
> http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
>
> By not 'well-standardised', i guess you mean that some people dont conform to the spec.
>
>
> paulm
>
You might also find the custom Photoshop section here :
http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/PhotoshopFileFormats.htm#50577413_pgfId-1039502
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