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Posts: 3
Registered: ‎10-25-2018
Accepted Solution
ECW bands and opacity mask


I would like to ask if anyone here knows what is the standard/proper way of exporting ECW file and how to make background pixels transparent.

So far I was using GlobalMapper software export and now I would like to start using ERDAS.

It is very important for me to make background pixels transparant or be able to clip orthophoto by using vector data and make all pixels outside the border transparent.

Using GlobalMapper software I get 4 bands, Band4 is coded as an alpha layer, after loading created ECW back into Globalmapper all background pixels are transparent. This file can be used also in ARCGis software and by defining that Band4 is opacity layer all background pixels disapper. Loading the same file into ERDAS I am not able to get all pixels transparent, there are many pixels along the clipping border which are almost black and they are visible.


Using Erdas IMAGINE 2018 software I managed to export ECW file, file has 3 bands and one extra opacity layer (null mask layer). 

After loading this file into ERDAS all background pixels are transparent, after loading into GlobalMapper or ARCGIS only black pixels (0,0,0) are transparent and all other pixels along and outside the clipping border are visible.

Please check attached file.



My main questions is:

Which ECW is correct. GlobalMapper 4bands or ERDAS 3bands and opacity layer?


I am also curious if there are any limitations in ERDAS export to ECW - maximum number of files, image size, overviews.




Thank you for help






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