Hi,
Can anyone answer these questions in order to aid my understanding of Rasters? Apologies but there are a few questions, some are general and some are specially FME related.
1. If a raster file contains multiple bands, do the bands ALWAYS have to be of the same numerical interpretation type? ( if this is true the presumably this would be due to a restriction of the data structure/model?) For example:
band{0}=Uint8
band{1}= Uint8
band{2}=Uint8
Or could you have mixed types as in:
band{0}=Uint8
band{1}= Int16
band{2}=Real32
band{3}=Int8
2. Within FME is there a way to ‘expose’ the interpretation type of band/s within a raster? If so what method could I use to do this? I have used RasterPropertyExtractor to obtain many details of the raster file, including the number of bands, but I cannot ascertain the actual interpretation types using this method. Essentially, I want to understand whether numerous raster files all have the same band interpretation type.
3. I have a mixed set of RGB raster files, either where the RGB bands are all UInt8; or, where the RGB bands are all Uint16.
I decided that I would consolidate them into 1 interpretation type.
Firstly I thought that I would try and convert the UInt8 files to UInt16. I used the RasterExpressionEvaluator to perform a test conversion. I only converted the r band just as a test, by Red16=A[0]. I then looked at the value of a given pixel both before and after the conversion, before pixel X was A[0] =100; and after pixel X was A[0] =100. I was sort of expecting the after value to be something like A[0] =25633 where ((100/256)*65536)); i.e. that the position of the value on the scale would be proportionally identical on the new scale. I presume that this is NOT the case as the value range Red8 (0-255) sits within the value range of Red16 (0-65535), therefore no change was applied as pixel X =100 was already 'valid'? Is this correct?
Consequently, if I do want to perform the 'proportional' conversions from either UInt8 to UInt16; or, UInt16 to UInt8, what method or formulas should I apply to complete conversions in either direction? Or should I NOT be doing this as it is this bad practice? Or, is it ok to convert in both directions? Or should I only convert down?
I am using FME Desktop 2015.1
Many thanks in advance.
Rob
