J.R.,
I don't think I have that alpha channel. Can't find one black & white that looks like the image. I got the image from google satellite. I used SBuilderX 3.14 to get the image and then use GIMP to make the Blend Mask, Water Mask and the BGL. The airport is in New York, KPTD.
If you got the imagery from Sbuilder it shouldn't be a problem with the alpha channel then. I wasn't sure where you'd gotten it. I'd try like _pawel says and make sure you have pure white where land's supposed to be in the watermask.tif.
I usually use NullValue = ,,,,0 in the watermask & blendmask sources, not sure if that will make a difference, here's one of mine that's known to work if that helps. Water & blend masks are 8 bit grayscale.
[/code]
[Source]
Type = MultiSource
NumberOfSources = 3
[Source1]
Type = TIFF
SourceDir = "."
SourceFile = "X40_KINF_WGS84_h2o.tif"
Layer = None
NullValue = ,,,,0
ulxMap=-82.3272394944647
ulyMap=28.8224055499843
xDim=2.90006734938693E-06
yDim=2.90006734938693E-06
SamplingMethod = Gaussian
[Source2]
Type = TIFF
SourceDir = "."
SourceFile = "X40_KINF_WGS84_blend.tif"
Layer = None
NullValue = ,,,,0
ulxMap=-82.3272394944647
ulyMap=28.8224055499843
xDim=2.90006734938693E-06
yDim=2.90006734938693E-06
SamplingMethod = Gaussian
[Source3]
Type = TIFF
SourceDir = "."
SourceFile = "X40_KINF_WGS84.tif"
Layer = Imagery
Variation = Day
Channel_BlendMask = 2.0
Channel_LandWaterMask = 1.0
NullValue = 0,0,0
PixelIsPoint=0
ulxMap=-82.3272394944647
ulyMap=28.8224055499843
xDim=2.90006734938693E-06
yDim=2.90006734938693E-06
[Destination]
DestDir = "."
DestBaseFileName = "X40_KINF_ortho_30cm"
DestFileType = BGL
LOD = Auto
CompressionQuality = 93
UseSourceDimensions = 1
[/code]