#2 Add tile or scanline-based encoding feature for large images.

[Rene Lindsay]

I'm looking for some way to compress a very large image to a file.
Unfortunately it seems libPGF requires the entire source image to be loaded into memory, before encoding, which is not practical for an image of 4TB. The ROI feature allows only part of the image to be read, but there seems to be no way to WRITE only part of the image.
(Please correct me if I'm wrong.)
Is it possible to modify libPGF to add a tile-based or scanline-based encoding scheme, like libtiff, or libjpg, to allow larger images to be compressed? The only solution I have right now, would be to use my own tiling scheme, maybe using sqlite to store tiles in a database, and compressing each individual tile, using libPGF, but then I would also have to re-implement a ROI feature, which makes libPGF's own ROI feature redundant.

[Christoph Stamm]

You are right. libPGF requires the entire source image to be loaded into memory before encoding, and the ROI feature is just for decoding.

Instead of blowing up libPGF with rarely used features, we pursue a different strategy. In our PGF related products we use a special library (PPPExt) for tiled images based on libPPP (PPP stands for PNG plus PGF). The tiles in such a tiled image are efficiently encoded in PGF or PNG format, and the tiles can be stored in different ordering schemes on external storage.

In addition to PPPExt a simple converter from tiled TIFF to PPPExt is available.

Since our open source resources are clearly limited, we provide PPPExt only on request.

[Rene Lindsay]

Thank you for your quick reply. PPPExt sounds like it's exactly what I'm looking for!
And since the images I need to compress, are already in GeoTiff format, the TIFF to PPPExt converter tool would come in very handy too. :)
I hereby respectfully request a copy.
Please can you provide a link, or email to me at rjklindsay@hotmail.com?
Thanks in advance.