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I want to convert TIF to ECW with FME. Some tif-pixels have values of 255/255/255:

enter image description here

After conversion these pixels have values of 254/254/254 or 253/254/252 or similar.

enter image description here

How can I achieve that 255/255/255 is not changed?

I need 255/255/255 in result because I want to set the border of the image (255/255/255) to transparent in AutoCAD Map.

To convert TIF to ECW I use these FME tools: Reader > RasterPaletteResolver > Writer

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    ECW compression is lossy and you can't keep the original pixel values exactly the same. However, I am remembering that native ECW compressor from ER Mapper had a selection for the background color which should mean that ECW has some mechanism for controlling off-site areas.
    – user30184
    Commented Jul 7, 2015 at 7:43
  • Thanks @user30184. Unfortunately I did not have ER Mapper.
    – Jens
    Commented Jul 7, 2015 at 8:23
  • Try to find a way for clipping the border out or perhaps you can somehow add alpha channel to image or introduce a mask on AutoCAD side.
    – user30184
    Commented Jul 7, 2015 at 8:37
  • Thanks for your hints @user30184. Due to the projection the content is not rectangular - so clipping will not be easy. I will try this approach: mosaic all TIFFs first (500 files, sum of 1.3 GB). Then convert this one large TIFF to one ECW.
    – Jens
    Commented Jul 7, 2015 at 9:09

1 Answer 1

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This problem is addressed in part by http://blog.hexagongeospatial.com/help-ecw-speckled-edges/

The only way to achieve consistent background color values after compression is by using an AllOpacity band which doesn't appear to be supported by the version of ECWJP2 SDK used in FME.

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