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Support ECW / JP2

The ECW (Enhanced Compressed Wavelet) and JP2 formats are standard compressing processes in many Hexagon Geospatial products. This discussion board focuses on the production and use of the ECW/JP2.
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Frequent Contributor
Posts: 86
Registered: ‎05-17-2016

Re: ECW Throughput and Decompression

Hi,

 

Which compression type (ecw or jp2) retains the pixel values and resolution of the original image? and can be used without Decompression for remote sensing such as spectral reflactance analysis.

Moderator
Moderator
Posts: 265
Registered: ‎11-16-2015

Re: ECW Throughput and Decompression

As I said before, you can use JPEG2000 with a compression ratio of 1 for numerically lossless.

With ECW and JPEG2000 you keep the resolution.

New Member
Posts: 1
Registered: ‎09-14-2017

Re: ECW Throughput and Decompression

So if compressing a DSM with a source range in values from say 0 to 400 (meters) using ECW this "slight change" in values will be manifest how?  Is it a linear relationship with 0-255?

Moderator
Moderator
Posts: 265
Registered: ‎11-16-2015

Re: ECW Throughput and Decompression

Hi,

As ECW v3 (not v2) supports 16bits unsigned, you could compress your DSM in ECW and keep the range [0 400]. But, as the ECW compression is not numerically lossless, some values may slightly change. It can be acceptable depending on your workflow or not.
If you want to use 8bits, you will have to truncate or rescale your range to [0 255].
If you want to keep exactly the same numerical values for your DSM, you will have to use JPEG2000 with a numerically lossless compression. You can do that with GeoCompressor for instance.

See the ERDAS ECW JP2 SDK user guide for more information: http://www.hexagongeospatial.com/technical-documents/erdas-ecw-jp2-sdk-user-guide

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