[gdal-dev] Questions about processing four band (RGBI) imagery

[Jonathan Moules]

Hi List,
  I have four band (RGB plus Infrared) imagery from some aerial photography
we've had flown. I've already used GDAL to create suitable optimised RGB
GeoTIFFs using this data and now want to do it with the Infrared band too.

The RGBI data is about 1TB uncompressed, currently stored as 2732 GeoTIFF
tiles compressed with LZW:

Files: SK1400.tif
>        SK1400.tfw
> Size is 8000, 8000
> Coordinate System is:
> PROJCS["OSGB 1936 / British National Grid",
>     GEOGCS["OSGB 1936",
>         DATUM["OSGB_1936",
>             SPHEROID["Airy 1830",6377563.396,299.3249753150316,
>                 AUTHORITY["EPSG","7001"]],
>             AUTHORITY["EPSG","6277"]],
>         PRIMEM["Greenwich",0],
>         UNIT["degree",0.0174532925199433],
>         AUTHORITY["EPSG","4277"]],
>     PROJECTION["Transverse_Mercator"],
>     PARAMETER["latitude_of_origin",49],
>     PARAMETER["central_meridian",-2],
>     PARAMETER["scale_factor",0.9996012717],
>     PARAMETER["false_easting",400000],
>     PARAMETER["false_northing",-100000],
>     UNIT["metre",1,
>         AUTHORITY["EPSG","9001"]],
>     AUTHORITY["EPSG","27700"]]
> Origin = (414000.000000000000000,301000.000000000000000)
> Pixel Size = (0.125000000000000,-0.125000000000000)
> Metadata:
>   AREA_OR_POINT=Area
> Image Structure Metadata:
>   COMPRESSION=LZW
>   INTERLEAVE=PIXEL
> Corner Coordinates:
> Upper Left  (  414000.000,  301000.000) (  1d47'35.68"W, 52d36'22.49"N)
> Lower Left  (  414000.000,  300000.000) (  1d47'35.83"W, 52d35'50.12"N)
> Upper Right (  415000.000,  301000.000) (  1d46'42.51"W, 52d36'22.40"N)
> Lower Right (  415000.000,  300000.000) (  1d46'42.68"W, 52d35'50.03"N)
> Center      (  414500.000,  300500.000) (  1d47' 9.18"W, 52d36' 6.26"N)
> Band 1 Block=8000x32 Type=Byte, ColorInterp=Red
> Band 2 Block=8000x32 Type=Byte, ColorInterp=Green
> Band 3 Block=8000x32 Type=Byte, ColorInterp=Blue
> Band 4 Block=8000x32 Type=Byte, ColorInterp=Undefined
>
>

My goal is to create a mosaiced GeoTIFF image with all four bands in it. It
should be as small as possible without serious quality degredation.


I've got some some questions as a result of my experiments so far:


   - "-co PHOTOMETRIC=YCBCR" - in gdal_translate this will fail saying it
   only works with 3 bands. Yet with gdaladdo, compressing overviews with
   "--config PHOTOMETRIC_OVERVIEW YCBCR" works fine (or at least gives no
   errors). Any reason for this?
   - Is there any special compression to use for four band imagery as I
   can't use YCBCR?
   - What's the best way to process the data? I'm using:

gdal_translate aerial.vrt aerial.tif -of GTiff -co BIGTIFF=YES -co
> TILED=YES -co blockxsize=512 -co blockysize=512 -co COMPRESS=JPEG -co
> JPEG_QUALITY=50 -a_srs EPSG:27700
> gdaladdo aerial.tif -r average --config COMPRESS_OVERVIEW JPEG --config
> JPEG_QUALITY_OVERVIEW 50 --config INTERLEAVE_OVERVIEW PIXEL --config
> PHOTOMETRIC_OVERVIEW YCBCR 2 4 8 16 32


   - How do I get GDAL to *not *set Band 4 to "Alpha" (which is what the
   above does).

Using GDAL 1.10.1

Thanks,
Jonathan

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