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In ArcGIS 10.6 I have a 3 Band tif image which has large areas which I do not want to display. I have created polygons of these areas and converted them to a raster tif in order to create a 4th band to use as an alpha channel to make areas transparent. I used the Composite band tool to create the 4 band raster but when I activate the alpha channel using this band the whole image becomes transparent and not just the defined areas.

The 4th Band consists of just 2 values 0 and 1. Is ArcGIS assuming that the extent of the 4th band is the transparent area and not just the pixels with a value of 1? How to I set the raster to only make pixel value 1 the transparent pixel.

I am aware than I can set a nodata color in ArcGIS but I need to try to do this using an alpha channel for a client.

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If you want your 1 values visible and your 0 values transparent, convert your 1 values to 255.

If you want your 1 values transparent and your 0 values visible, convert your 1 values to 0 and your 0 values to 255.

Alpha channels are 0-255 where:

  • 0 = fully transparent
  • 255 = no transparency
  • 1 - 254 are decreasing transparency/increasing opacity.

When you set your band with 0 and 1 as the alpha channel, 1 was treated as being almost completely transparent.

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