[R] Converting 16-bit to 8-bit encoding?

[Matt Shotwell]

OK. I'm going to copy this back to R-help too.

With R, we can convert a file of 8-bit integers to 16-bit integers like so:

# Create a test file of 8-bit integers:
con <- file("test.8", "wb")
writeBin(sample(-1L:4L, 1024, TRUE), con, size=1)
close(con)

# Convert test.8 to test.16
icon <- file("test.8", "rb")
ocon <- file("test.16", "wb")
while(length(dat <- readBin(icon, "integer", 1024, size=1)) > 0)
     writeBin(dat, ocon, size=2)
close(icon)
close(ocon)

This assumes (without considering a more formal description of the 
format) that the file and your computing platform agree on how 
multi-byte signed integers are represented.

Hope that will get you going.

On 04/21/2011 11:02 AM, Brian Buma wrote:
> Apologies.  The 8-bit file (the one that needs to be converted) is just
> a series of integers, -1 to 4, which is no doubt why they are encoded in
> 8 bit.  They don't need to be changed numerically, just put in a 16-bit
> encoding.  No meta info, headerless.  All the data is MODIS satellite
> imagery.
>
> I have been using the "raster" program to visualize things, and
> processing (when I get that far) will be done in that program mainly.
> I've used that program on a different project, and it seemed to work
> well.  The actual program that can't handle two different inputs is
> Timesat, a phenology-program (not R).  I was thinking that R could
> probably do this conversion quick and easy (fairly), but haven't figured
> out how to yet.
>
> As an example, I have an NDVI file (flat binary, 16bit encoding)- so a
> string of numbers, 4450, 4650, etc...  The associated quality file is
> another string, 1,1,2,1,0, etc.  It's encoded as an 8bit file.
> Conceptually, all it needs (I think) is to be read in and resaved in the
> less memory-efficient 16-bit format.
>
> Thanks!  Sorry if the explanation isn't clear.
>
>
>
> On Thu, Apr 21, 2011 at 9:50 AM, Matt Shotwell
> <Matt.Shotwell at vanderbilt.edu <mailto:Matt.Shotwell at vanderbilt.edu>> wrote:
>
>     On 04/21/2011 10:36 AM, Brian Buma wrote:
>
>         Hello all-
>
>         I have a question related to encoding.  I'm using a seperate
>         program which
>         takes either 16 bit or 8 bit (flat binary files) as inputs (they
>         are raster
>         satellite imagery and the associated quality files), but can't
>         handle both
>         at the same time.  Problem is the quality and the image come in
>         different
>         formats (quality- 8bit, image- 16bit).  I need to switch the
>         encoding on the
>
>
>     I think some more detail about these files is necessary. What do
>     these 16/8 bit quantities represent? Are these files just a sequence
>     of such quantities, or is there meta information (i.e. image dimension)?
>
>
>         quality files to 16 bit, without altering anything else (they
>         are img files
>         right now).  I imagine this is a fairly simply process, but I
>         haven't been
>
>
>     Does 'img files' indicate that these files are formatted according
>     to a standard?. Finally, are you using some R code to manipulate
>     these files? Have an example, including data?
>
>
>         able to find a package or anything which can tell me how to do
>         it- perhaps
>         I'm searching the wrong terms, but I did look.  Is there any
>         methods to do
>         this quickly?  Ideally, the solution would involve reading in a
>         list of
>         files and replacing the original with the new, 16 bit version,
>         as I have
>         over 300 files to convert.  I hope that's clear.  Thanks in advance!
>
>
>
>     --
>     Matthew S Shotwell   Assistant Professor           School of Medicine
>                          Department of Biostatistics   Vanderbilt University
>
>
>
>
> --
>
>
> Brian Buma
> PhD Candidate
> Ecology and Evolutionary Biology / CIRES
> University of Colorado, Boulder
>
> Brian.Buma at colorado.edu <mailto:Brian.Buma at colorado.edu>
>


-- 
Matthew S Shotwell   Assistant Professor           School of Medicine
                      Department of Biostatistics   Vanderbilt University