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Hi there, A quick question: Is there any way to compress the single
point floating point data? Apparently most of the research and
development work focuses on fixed point compression.

James
www.go-ci.com

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DigitalSignal wrote:
> Hi there, A quick question: Is there any way to compress the single
> point floating point data? Apparently most of the research and
> development work focuses on fixed point compression.

What do you want to achieve? Range compression? Storage reduction?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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On Nov 6, 5:19 pm, DigitalSignal <digitalsignal...@yahoo.com> wrote:
> Hi there, A quick question: Is there any way to compress the single
> point floating point data? Apparently most of the research and
> development work focuses on fixed point compression.
>
> Jameswww.go-ci.com

Isn't this what is called "scalar quantization"?

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On Nov 6, 5:19=A0pm, DigitalSignal <digitalsignal...@yahoo.com> wrote:
> Hi there, A quick question: Is there any way to compress the single
> point floating point data? Apparently most of the research and
> development work focuses on fixed point compression.
>
> Jameswww.go-ci.com

James,

Do you mean single "precision" floating-point data?

A lot of the work compares compressed data rates to fixed-point
quantized data rates, but that does not mean that the data to be
compressed was not floating point before it was compressed (or
quantized).

Dirk

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DigitalSignal wrote:

> Hi there, A quick question: Is there any way to compress the single
> point floating point data? Apparently most of the research and
> development work focuses on fixed point compression.

Fixed point data that doesn't fill up its range compresses
well with many algorithms.  Floating point data with noise
in the low order bits won't compress well.  The results
depend on the statistics of the bits, independent
of their source.

-- glen

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Well, to reduce the number of bits you need to store, you could throw away
some mantissa bits.  That's probably the simplest form of compression, but
it is lossy.

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On Thu, 06 Nov 2008 14:19:42 -0800, DigitalSignal wrote:

> Hi there, A quick question: Is there any way to compress the single
> point floating point data? Apparently most of the research and
> development work focuses on fixed point compression.
> 
> James
> www.go-ci.com

Yes.  Set all the values in your vector to zero.  Then transmit the 
number of samples in your vector.

Clarify your question and maybe you'll get a meaningful answer.

Lossy?  Lossless?  Any specific type of input data, such as still 
pictures, video, generic audio or voice?  There are any number of lossy 
compression algorithms that are just as meaningful with floating point 
data as the source stream as with fixed point; but if you're talking 
lossless compression then you're pretty much down to the algorithms you 
find in zip, and their aunts, uncles, cousins and in-laws.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

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On 6 Nov, 23:19, DigitalSignal <digitalsignal...@yahoo.com> wrote:
> Hi there, A quick question: Is there any way to compress the single
> point floating point data?

It depends entirely on the statistics of the data.
Plain text is easy to compress because there are
few cases to consider (256 charcters) and the
probability of occurence is far from uniform over
the alphabet.

It might be that the entropy of FP data, when viewed
per byte or 16-bit word is so high that 'naive' text
compressing algorithms don't work well.

Rune

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Sorry, I should make it clearer. We tried to find a way to compress
the single precision floating point data streams losslessly. As a
general case, the data acquisition system stores time domain data up
to a few gigabytes. It is expensive to store the data in the portable
device and slow to transfer them.

James
www.go-ci.com

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DigitalSignal wrote:

> Sorry, I should make it clearer. We tried to find a way to compress
> the single precision floating point data streams losslessly. As a
> general case, the data acquisition system stores time domain data up
> to a few gigabytes. It is expensive to store the data in the portable
> device and slow to transfer them.

To compress it you (or a compression program) have to find some
pattern to the data such that it can be coded more efficiently.

For fixed point data that pattern will often be high order
zero bits.   LZW and related algorithms will usually find them
and compress them out fairly well.  If, for example, you stored
12 bit random data in 16 bit words, LZW would compress that
down pretty close to 12 bits each.

You say lossless, but in most cases there has already been loss
in the conversion/arithmetic operations on floating point data.
Reasonably often there is no useful information in the low
bits of a floating point value, but you and the compression
algorithm don't know that.

-- glen

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