Making non-image areas transparent

[SavannahRob]

Hi all,

I have a set of 11-bit grayscale TIFFs from satellite. They've been georectified and as a result many of them have no-data areas that were outside the capture area. You can imagine a black square of no-data with a smaller square of real imagery inside it, turned at some angle. Only the no-data areas have a zero value.

We'd like to turn these into MrSid 4 images with transparency in the no-data areas. Anyone know how we can do this?

Something we've struggled with is that at some point, we have to convert images from 11-bit to 8-bit before going to MrSid. This redistributes the values so that dark features end up with a zero value- the same as no-data. When we add transparency, the dark areas end up transparent when they should not be.

[rparker]

Could you share some of these images and your situation with support@lizardtech.com?

We'd like to take a look at them and see if we can help.