🚀 go-pugleaf

In article <17124@acorn.co.uk> David De Vorchik writes:
>We are currently trying to decode some TIFF files that originated on a NeXT
>box.  These icons have a strange samples per pixel value (0x20002), we
>assume this is something to do with masking of the image (as some of them
>are icons).

Bizarre. NeXTSTEP never generates TIFFs with that spp; spp is always 1, 2, 3,
or 4.  In fact, given that the SamplesPerPixel tag is a short, the value
you specify doesn't look right. If it were to be 2 (which seems likely), then
you probably have a grayscale image with alpha.

Images with alpha aren't too complicated; they just have an extra channel
holding the transparency information, and the actual image itself is
premultipled with alpha. The alpha is stored as the last channel of data.

NeXTSTEP 2.x denotes alpha with the private MATTE tag; NeXTSTEP 3.0 uses
the newly created standard ExtraSamples tag.

Ali, Ali_Ozer@NeXT.com