Alpha-mask vs. merged-Transparency in PSD format

Hi,

I'm trying to read merged RGBA data from PSD format. "Image data" section contains channels (RGBAA... where first A might be a merged transparency or Alpha mask). Can someone tell me how to know what is stored in first A? I noticed that:

• when image contains no transparency, but has at least one Alpha mask, then first Alpha channel will contain that alpha mask
• when image contains transparency, then first Alpha channel will contain merged transparency and other Alpha channels will contain alpha masks

So how do I reliably differentiate between Transparency and Alpha mask in first Alpha channel?

Regards,

Paulius Liekis

Unity Technologies