Thank you.
Question
size of raster file
Hi again, while I am trying with the help of support solve one problem, comes new one :) Ok, maybe it is not a problem, but I need explanation. If I have, for instance, 10 geotiff files, each has 1 Mb of size, how could be possible that one jpeg2000 mosaick file of those 10 files is ten times bigger i.e. 100Mb even If I used compression 20% . What kind of new informations appeared ?
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Hi,
one explanation could be that the TIFF was stored as a monochrome bitmap (b/w only, no greyscale) while the resulting JPEG was saved with full color information, such as RGB bands and perhaps even an alpha channel. The on-screen representation would not have to differ although the internal representation could be vastly different, explaining the differences in file size.
Also, note that the compression level set in FME does not translate directly to a percentage gain in the file size.
David
Geotiff files are stored with color information not using alpha band, same would be expected with jpeg2000 according to RasterMosaicker parameters. Nodata overwrites data is set NO, merge palettes YES, Accumulate Attributes YES.
In this case, I would try to use the ImageMagick command "identify" on both the input and output files to verify what is going on.
In particular, look at the colorspace and channel depth values. I would also check the number of pixels to make sure that there has been no upsampling.
You can download ImageMagick here, it is free.
David
+59- Safer
Partly it would depend on how the data was laid out and how it was mosaiked.
Remember, a raster dataset has to be rectangular. If the 10 files were arranged in a diagonal arrangement then the bounding box could be 10x the size of the combined files - just as you describe. In other words the output has to include any 'dead' space inside the bounding box, even if it isn't covered in the source data.
One other possible difference is that TIFF allows non-square pixels, whereas jpeg doesn't - so if your TIFF pixels were rectangular there would need to be more of them in the TIFF output.
I'd be surprised if FME were doing any sort of resampling - but do query these in the FME Viewer/Data Inspector and see what info is returned. In particular look for the Raster Properties such as:
Number of Rows
Number of Columns
Cell Origin
Cell Spacing
(Raster) Origin
Extents
Hope this helps
Mark
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