Cassini maps

Peter,

If recall those BIG aerial coverages of south glos/wiltshire I gave you were JP2? I think I sent them in that format for convenience due to size. Truth be told, I still have the original TIFFs of them and ER Viewer just seems to be able to handle them better.

BTW, make sure you've got the latest version of ER Viewer. Turned out they've made quite a few updates since I last got it. Maybe a newer version will handle the JP2s better.

Oh dear...

Just out of curiosity I looked up the ECW format: en.wikipedia.org/wiki/ECW_%28file_format%29 and had a chat with a bloke at work who specialises in image optimisation and formats.

He said that most likely it could be that the wavelet compression used in ECW/JP2 could be taking more of your CPU and memory to decompress due to the mathematics involved in recreating the chunks. He said that TIFF, though larger on disk, requires less computer processing to display as the data is just stored as a stream of pixel data.

In his infinite wisdom he said it's a trade off between file size and processing speed - ECW/JP2 will save space and the cost of loss of fidelity and processing time versus TIFF which saves fidelity and processing but takes up more space.

The conversation then fell into a hole about discreet cosine transforms and offloading wavelet processing to GPU's so I bought another beer...

OneEighthBit;161652 wrote:

The conversation then fell into a hole about discreet cosine transforms and offloading wavelet processing to GPU's .....

Around this time the conversations about graphics formats here seem to turn to how effective compressed graphics formats are for carrying all sorts of other data of use to cryptographers and terrorists...I usually need an analgesic by then.

(The tiff versions of the England/Wales/Scotland maps mentioned by Peter and Martin total about 250Gig. On this fairly ancient PC with 2 gig RAM and a steam processor the tiffs open fairly quickly in irfanview / gimp...the jp2 versions I gave up trying to open)