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Reading HDF5 signed bytes gives strange results [message #49856]

Tue, 22 August 2006 09:38

Maarten[1]
Messages: 176
Registered: November 2005

Senior Member

Hi,

When reading a signed byte from and HDF5 file I get all kinds of nasty
results. Of course, IDL doesn't know about signed bytes, but I expect
it to be nice to the bit-images, and read -127 (signed) as 129
(unsigned). However, none of that seems to happen with the routines I
use.

When reading with h5_parse(file, /read), I get the fields, with -127
(the fill value, in case you're wondering) replaced by 129, as expected
in 2-complement notation. All would be well, If the rest of my software
could use h5_parse. But I can't use it for various reasons.

When using h5f_open, h5d_open, h5d_read & friends, the value -127 is
repleaced by 0. The fill value (an attribute) is replaced by 0. And 0
is a perfectly valid data-value. When I then try to filter for fill
values, I throw out quite a few valid values.

How can I force the field to be read differently so that values < 0 end
up at values > 127, while not resorting to h5_parse?

Maarten

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[Message index]

		Reading HDF5 signed bytes gives strange results By: Maarten[1] on Tue, 22 August 2006 09:38
		Re: Reading HDF5 signed bytes gives strange results By: Maarten[1] on Wed, 23 August 2006 23:36
		Re: Reading HDF5 signed bytes gives strange results By: David Fanning on Wed, 23 August 2006 08:23
		Re: Reading HDF5 signed bytes gives strange results By: Maarten[1] on Wed, 23 August 2006 08:17

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