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New Contributor
Posts: 3
Registered: ‎10-25-2018
Accepted Solution

ECW bands and opacity mask

Hello,

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

Regards

KAte

 

 

 

Highlighted
Staff
Posts: 580
Registered: ‎02-02-2016

Re: ECW bands and opacity mask

Hi Kate,

 

The ECW file format is a proprietary image format developed by Hexagon Geospatial. There is no file size limit for ECW images.

 

Regarding the display of your ECW images in ArcGIS I would recommend that you install the ERDAS ECW Plug-in for ArcGIS Desktop. That should remove the salt and pepper effect around the boundary of your data. You can find this free plug-in for ArcGIS on our downloads website.

 

Hexagon Geospatial Product Downloads: https://download.hexagongeospatial.com

 

Kind regards,

 

Stephen Bent

Hexagon Geospatial Support

New Contributor
Posts: 3
Registered: ‎10-25-2018

Re: ECW bands and opacity mask

Thank you for your reply

 

Today I am writing to get more information about ECW export from ERDAS IMAGINE.

I would like to know what is the best way to export one ecw file from many single tiff files.

My approach was to open all tiff files in ERDAS by using Multiple Images in Virtual Mosaic option.

I am not sure if it is better to create Virtual mosaic or load all files separately into the workspace.

Do I need pyramids in TIFF files for better/faster displaying or processing? Should I have internal or external pyramids? What file format is used in ERDAS for pyramids?

Can I define resampling method in the ECW export? It looks like only nearest neighbor resampling method is available/active.

Regards

Kate

Staff
Posts: 580
Registered: ‎02-02-2016

Re: ECW bands and opacity mask

Hi Kate,

 

You have a few options available in ERDAS IMAGINE to perform this task.

 

You can use the Export tool. Set the format to ECW and select your multiple input TIFF images as a virtual mosaic. You can’t change the pixel size with the Export tool, thus there is no need to choose a resampling method.

 

You could load your TIFF images into MosaicPro and write the output image to ECW format. You can change the pixel size of the output ECW image using MosaicPro and you can choose the resample method (Nearest Neighbor, Bilinear Interpolation, Cubic Convolution, Bicubic Spline, LaGrange).

 

Your input TIFF files do not have to have pyramids for the export to ECW process, but pyramid layers will speed up the display of the individual TIFF images if you plan on viewing them later. I prefer to have internal pyramid layers. But if you want the pyramid layers stored externally they use the *.rrd file format (RRD - reduced resolution dataset).

 

Regards,

 

Stephen Bent

Hexagon Geospatial Support

New Contributor
Posts: 3
Registered: ‎10-25-2018

Re: ECW bands and opacity mask

Thank you

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