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Support the ECW opacity band for raster display

Status: Delivered
by on ‎10-11-2017 08:23 AM - last edited on ‎10-23-2017 08:52 AM by Technical Evangelist

As a GeoMedia user of ECW files, I want raster display to support the ECW opacity band, so that I can avoid speckled edges or black collars and have sharp clean edges on my raster display

Status: Delivered

Delivered with the GeoMedia Desktop 2020 release, by setting the transparent color to black (0,0,0) on the Style Propertes dialog.

by Technical Evangelist
on ‎10-13-2017 06:15 AM
Status changed to: Needs additional information

Kirill, I need help understanding the request so I can clarify a few points in the Idea.  There is already an opacity / translucency / alpha channel setting for raster legend entries in GeoMedia:  right-click the legend entry, Style Properties..., then see the Translucency control.  Based on this, and based on your statements about black color background and sharp edges, I think translucency is not what you are looking for - it applies uniformly to all pixels and simply controls "see-through".  Instead my guess is that you are interested in the ability to set transparency (complete masking) of certain background pixels only, of a certain color or colors.  But this too is already available in GeoMedia, at least for certain image types.  On the same dialog, see the "Transparent color" and "Transparent pixel values" settings.  Based on this information, can you clarify your request further?  - Hal

on ‎10-13-2017 08:24 AM

Hal hi!
Thanks for your feedback.

You're right. I'm talking not about Translucency. And I'm not talking about "Transparent color" setting, which is well-known. It doesn't work for images with alpha-channel parameters. Attached is an example, where I set black color as a transparent color. And it doesn't work, as background of my ECW image has many gradations of black color, different from pure black one which I have set. 





So, what I'm asking for is to add support for alpha-channel, in order to let users set transparency for the whole background.

by Technical Evangelist
on ‎10-17-2017 05:23 AM

Kirill, I still think we are not using some of the words the same way :-).  Alpha channel is specifically about translucency/opacity, it is about how something should be rendered in a way that it blends it with what is beneath it in the display.  What you are speaking of is (I think!) an ability to completely blot out (make transparent) certain pixels that form the background - but instead of a single "transparent color", to do so with a wider range of colors or pixel values because one shade of "black" is not sufficient to achieve transparency of a lot of background pixels that are small variations of blackness.  Am I understanding correctly?


If so, then tell me about your experience with the control just below the one you highlighted above; "Transparent pixel values".  Although applicable only to some image types I believe, it is intended to permit multiple pixel values to be designated as transparent.  I believe a third-party tool is sometimes required to get the pixel values that you wish to make transparent.  Does this approach not work for you?  - Hal

on ‎10-23-2017 04:03 AM

Hi Hal,


Below is our experience with opacity / transparency of ECW in 3 (!) different products: Imagine, ArcGIS, QGIS.

We would like to have the same functionality in GeoMedia, or even more - to move out all background for ECW, keeping the edges clean and sharp.

Hope it is possible.



There is a ECW file with the opacity layer:



It is recognized automatically in IMAGINE:



In ArcGIS there is also an option to specify the opacity level.










In QGIS a similar option is available as well:




Whereas in GeoMedia we can only specify color for transparency or indicate particular pixel values. These options have nothing to do with the opacity layer.










by Technical Evangelist
on ‎10-23-2017 05:03 AM

OK, Kirill, I think I am finally understanding.  You are speaking of something present within an ECW file, intended to deal with certain ECW compression artifacts.  It is something that I am unfamiliar with, and which has a confusing (to me) name which overlaps with other uses of the same terminology.  This article helped me some:  My proposed amendment to your story is: “As a GeoMedia user of ECW files, I want raster display to support the ECW opacity band, so that I can avoid speckled edges or black collars and have sharp clean edges on my raster display.”  Is this sufficient for you?  - Hal

on ‎10-23-2017 05:37 AM
Hal,   I also saw that article reg speckled edges in ECW.   Ok, we could rename my story as you've suggested.   Thanks!
by Technical Evangelist
on ‎10-27-2017 07:38 AM

Don't know if it helps or not, but the terminology used in ERDAS IMAGINE is Value-based vs Mask-based (usually in the context of NoData).


Value-based is when you say, for example, DN value 0 should be transparent. 


Mask-based is when you have a dedicated layer which defines the spatial locations to be considered transparent (or semi transparent). That mask is independent of "real" DNs - any given pixel location in the mask could be a DN of 0, 1,2,255, 2047, etc (in any "real" bands of a multispectral image).


The ECW (v3) Opacity Layer is a Mask-based approach. Confusingly ECW v2 only used Value-based transparency. TIFFs can have an Alpha Channel, which is another kind of Mask-based transparency.

on ‎10-30-2017 04:50 AM - last edited on ‎10-30-2017 05:08 AM by Technical Evangelist

Hi Ian!

Yse you're right.
That's why we use ECW 3.0 and ask for the same approach "Mask-Based" in GeoMedia, as it is in Erdas Imagine.

by Technical Evangelist
on ‎01-01-2018 08:04 AM
Status changed to: Candidate
on ‎07-02-2018 07:42 PM

my experience with large ECW files and the unsolvable edges in GeoMedia is so frustrating I have abandoned them. We now use all the small tiles that have "clean" edges only ie cut to tile edge. This renders many aerial images unusable.