External overview override not mixed with internal jpeg2000 overviews

[warmerdam]

Support has been implemented in the JP2KAK driver for external overviews. When available they are used in place of internal jpeg2000 overviews. However, currently any external overviews being built causes all internal overviews to be ignored while the desired behavior is for the internal overviews to be used as a fallback when the external overviews are unavailable.

[warmerdam]

David Taubman reports:

> Indeed, the image has no doubt been compressed without the
> use of precincts and with very large tiles so it is absolutely
> unsuitable for random access. I imagine it does not have any
> random access pointers inside it, but even if it does there cannot
> be sufficient of them to be useful because there are not enough
> distinct entities to point to.
>
> Interactive apps like kdu_show open the codestream in a persistent
> mode, which means that information which must be parsed
> sequentially will not be flushed from memory -- otherwise the
> interactive app would have to parse it all over again from scratch.
> For an image like this, however, you could set up a decompression
> engine to decompress/render just a single region of interest while
> keeping the codestream in non-persistent mode -- and then if
> you want another region, you can open the whole thing again from
> scratch, again in non-persistent mode. To see how effective this
> would be in keeping memory down, you could invoke kdu_expand
> on a reduced region of interest (-region argument) and see
> how much memory it consumes.

David Burken also indicated on the list that he has had success reducing memory use with use of the region decompressor on an image that appears to have the same configuration.

I'm going to experiment with the region decompressor, though I suspect we will be sacrificing speed for reduced memory footprint.

[warmerdam]

Disregard last comment, it ended up in the wrong ticket.

[warmerdam]

It turns out it is not desired to mix internal and external overviews ... closing.