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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: 84
Registered: ‎05-17-2016
Accepted Solution

ECW Throughput and Decompression

Hi All,

 

What is the average compression throughput for GeoCompressor 2016? I've tested it with sample datasets but finds it averagely to be 20MB/Sec for lossy which seems much slower as desired. Could there be any problem with this?

Secondly, can the compressed files in ECW format be used for further remote sensing analysis? and how we decompress the ecw files to the original dataset?

 

Thanks,

 

Technical Evangelist
Posts: 768
Registered: ‎07-30-2015

Re: ECW Throughput and Decompression

Here is report from one of my GeoCompressor 2016 ecw compression job. The throughput is 43.5 MB/sec.
Duration: 0 hours 0 mins 10 seconds
- Read: 4517 ms
- Write: 5326 ms
- Reassembly: 78 ms
Target Ratio: 20:1
Actual Ratio: 18.3:1
Throughput: 43.5 MB / sec
Method: Tile
Threads: 2

 

ECW file is lossy, and it doesn't keep the original digital number from the remote sensing data.

 

best
haiyan

Frequent Contributor
Posts: 84
Registered: ‎05-17-2016

Re: ECW Throughput and Decompression

Thanks Haiyan.

 

How do we obtain a lossles compression using geocompressor? and how do we decompress the ecw file?

Can a lossless compresion be used for further analysis?

Technical Evangelist
Posts: 768
Registered: ‎07-30-2015

Re: ECW Throughput and Decompression

For lossless compression, you have to use JP2 instead of ECW. lossless compressed JP2 will keep original digital number from remote sensing data, so can be used for further analysis.

best
haiyan

Frequent Contributor
Posts: 84
Registered: ‎05-17-2016

Re: ECW Throughput and Decompression

Hi Haiyan,

 

Can the JP2 format be decompressed to obtain the orignal image? in other formats such as TIFF? How can this be done?

Technical Evangelist
Posts: 768
Registered: ‎07-30-2015

Re: ECW Throughput and Decompression

If JP2 is lossless compressed, and then it can be decompressed to TIFF with original Digital number. But decompression is beyond the geocompressor, you have to use ERDAS IMAGINE to decompress JP2 (or using ECW/JP2 SDK if you are developer)

 

best
haiyan

Frequent Contributor
Posts: 84
Registered: ‎05-17-2016

Re: ECW Throughput and Decompression

Does the target rate for lossless compression using JP2 format affect the output interms of retaining the original digital number from the remote sensing data? What's the recommended rate for the best lossless compression which can be used for further Photogrammetric work?

Frequent Contributor
Posts: 84
Registered: ‎05-17-2016

Re: ECW Throughput and Decompression

Hi,

 

Does the target rate for lossless compression using JP2 format affect the output interms of retaining the original digital number from the remote sensing data? What's the recommended rate for the best lossless compression which can be used for further Photogrammetric work?

Technical Evangelist
Posts: 768
Registered: ‎07-30-2015

Re: ECW Throughput and Decompression

[ Edited ]

The target ratio is used as a goal, but the compressor engine will also maintain the quality. So, depending on the input image characteristics, when you compress with a 20:1 target, the actual compression rate may be higher or lower. As long as you use lossless JP2, the digitnal number will stay the same as original input.

 

best

haiyan

Moderator
Moderator
Posts: 257
Registered: ‎11-16-2015

Re: ECW Throughput and Decompression

Hi Ksewe

 

To have a numerically lossless compression you need to compress in JPG2000 with a target ratio of 1. In that case, you keep the original values of the pixels. In that case, you can convert back to Tiff and have exactly the same pixels values. It is interesting for some remote sensing computations. I don't think you need that for a photogrammetric work?
If you need a visually lossless compression, you can choose ECW (or JPG2000) with a higher target ratio: up to 15-20 with multiband input and up to 10 for single band image. The pixels values will slightly change but visually you will not see any difference. 

 

Florent

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