Why does ArcGIS 10 not support TIFF6 transparency?

[AndrewBefus]

I have created a Flex program that outputs TIFF6 format (GeoTiffs). They render in ArcGIS fine except for transparency, which is displayed as opaque.

It's not like TIFF6 transparency is difficult to encode or decode (two extra lines of code extract alpha channel from RGB), so why does ArcGIS choose not to support it? Certainly PNG transparency works, but then you have to write auxiliary files for georeferencing. GeoTIFF is much neater and more flexible than PNG, so why scrooge on the features ESRI?

Alternatively, is there any future plans to support GeoPNG or include transparency with GeoTIFF? Or do something that allows georeferencing and transparency information to be stored in a single file?? Too much to hope for?

[Luke_Pinner]

A couple of workarounds are:

1 - Manually set the 4th band as alpha in the layer properties->symbology
2 - Write an internal/external mask. ArcGIS understands these, though I have no idea if Flex can write these (I use gdal).

[AndrewBefus]

Thank you for your help.

I'll try writing an internal mask to the file using gdal.

I've got full control on how my TIFF files are written (My program pieces them together bit by bit).

The manual transparency is not needed, since my TIFFS are palette-mapped. Thus if the user wants to make any of the features transparent manually they can just edit the palette in symbology.

What I was hoping for was to make the pixels vary in transparency (not simply opaque or transparent). I'll look into doing this with a mask. My alternative is to use the ArcGIS Flex API and make a mapping program within my program. Then I can interpret TIFF transparency the way it is supposed to be interpreted, though this will probably take weeks to complete and I'll get paid nothing for it.

[Luke_Pinner]

Sorry, the masks are 1bit - either visible or not.