"16-bit" mode.

Mike Russell wrote:

Mike Engles wrote:
...
[re linear encoding of specialized pixel data values]

Is the same true for imaging from spacecraft, interplanetary or
otherwise or is gamma encoding done before transmission?

Yes. Gama encoding compresses some data values, and there is no reason to
do this to raw data from a spacecraft.

Here's an article that may interest you, by Alvy Ray Smith, on the
distinction of work and display color spaces.
http://alvyray.com/Memos/MemosMicros...rAlphaQuestion
--

Mike Russell
www.curvemeister.com
www.geigy.2y.net


Hello

What I have just read chimes with everything I think should happen in
digital imaging. It does completely contradict everything that has been
written about gamma encoding in these and other forums with the
necessity for gamma to maximise the use of available bits.

ftp://ftp.alvyray.com/Acrobat/9_Gamma.pdf

Yet this guy seems to be a pioneer of digital imaging.

Also why is image data from spacecraft and astronomy not gamma
encoded.It is after all digital photography. They must be transmitting/
recording in at least 18 bit. That is the bit level that Chris Cox et al
say is the minimum necessary for linear images, without gamma encoding.

It does seem that what we have today is two types of digital imaging.
One is the truly scientific one that uses ALL linear data. The other is
a convenient engineering one that delivers the goods simply, by pre
compensating the linear data to display on non linear displays.

Engineers were always happy with approximations.

Mike Engles

Mike Russell wrote:

Mike Engles wrote:
...
[re linear encoding of specialized pixel data values]

Is the same true for imaging from spacecraft, interplanetary or
otherwise or is gamma encoding done before transmission?

Yes. Gama encoding compresses some data values, and there is no reason to
do this to raw data from a spacecraft.

Here's an article that may interest you, by Alvy Ray Smith, on the
distinction of work and display color spaces.
http://alvyray.com/Memos/MemosMicros...rAlphaQuestion
--

Mike Russell
www.curvemeister.com
www.geigy.2y.net


Hello

What I have just read chimes with everything I think should happen in
digital imaging. It does completely contradict everything that has been
written about gamma encoding in these and other forums with the
necessity for gamma to maximise the use of available bits.

ftp://ftp.alvyray.com/Acrobat/9_Gamma.pdf

Yet this guy seems to be a pioneer of digital imaging.

Also why is image data from spacecraft and astronomy not gamma
encoded.It is after all digital photography. They must be transmitting/
recording in at least 18 bit. That is the bit level that Chris Cox et al
say is the minimum necessary for linear images, without gamma encoding.

It does seem that what we have today is two types of digital imaging.
One is the truly scientific one that uses ALL linear data. The other is
a convenient engineering one that delivers the goods simply, by pre
compensating the linear data to display on non linear displays.

Engineers were always happy with approximations.

Mike Engles

In message ,
Timo Autiokari wrote:

And, there is no reason to do that to images from digital cameras
either, just like Adobe shows to us, the ARC (like most of the other
conversion sw too) perform all the processing in the linear domain.

I'm not so sure that ACR works in a totally linear domain. Images
exposed with bracketing, and compensated to be the same with the
exposure slider, may have equal mid-tones, but the shadows and
highlights will display that a different gamma is used. If you drag the
ACR exposure slider to the left, after it runs out of "hidden
highlights", it stretches the highlights so that 4095 in the RAW data
stays anchored at 255 in the output, and never gets darker. That is not
linear exposure compensation.

Optimally, I think that a RAW converter should have two basic exposure
controls; one to scale the linear data for exposure adjustments, and
another control to fit that to an output curve.

Why, for the same reason why linear processing os done in scientific
imaging also, to avoid the Gamma Induced Errors.

--


John P Sheehy

"Mike Engles" wrote in message
...
SNIP
Also why is image data from spacecraft and astronomy not
gamma encoded. It is after all digital photography.

Not necessarily. There is a difference between photometric data (e.g.
spectral reflection/absorption/emission in certain bands), and
pictorial imaging (e.g. stereo pairs in either visible light bands or
mixed with other spectral data).
One common issue between them is the desire to reduce quantization
errors (at least half of the LSB) to a minimum. Gamma encoding
provides a visually efficient encoding, but it can underutilize the
capacity at the lower, and overutilize (=additional quantization
errors) at the higher counts. Then there is the trade-off caused by
limited transmission bandwidth, and there is only so much one can do
with compression...

Bart

"Mike Engles" wrote in message
...
SNIP
Also why is image data from spacecraft and astronomy not
gamma encoded. It is after all digital photography.

Not necessarily. There is a difference between photometric data (e.g.
spectral reflection/absorption/emission in certain bands), and
pictorial imaging (e.g. stereo pairs in either visible light bands or
mixed with other spectral data).
One common issue between them is the desire to reduce quantization
errors (at least half of the LSB) to a minimum. Gamma encoding
provides a visually efficient encoding, but it can underutilize the
capacity at the lower, and overutilize (=additional quantization
errors) at the higher counts. Then there is the trade-off caused by
limited transmission bandwidth, and there is only so much one can do
with compression...

Bart

wrote in message
...
In message ,
SNIP
I already told what the data was - a binary file with the
16-bit unsigned values 0 through 65535. That's it:

00 00 01 00 02 00 03 00 .... fb ff fc ff fd ff fe ff ff ff

load as .raw, 256*256, 1 channel, 16-bit, IBM/PC, 0
header.

As a precaution, do make sure that you have set the same gamma for
your RGB *and* Gray working spaces and switch the "Use Dither" for
8-bit channel conversions to off. It should not matter when you load
the data as "raw" data, but just to make sure they don't interfere.

Bart

wrote in message
...
In message ,
SNIP
I already told what the data was - a binary file with the
16-bit unsigned values 0 through 65535. That's it:

00 00 01 00 02 00 03 00 .... fb ff fc ff fd ff fe ff ff ff

load as .raw, 256*256, 1 channel, 16-bit, IBM/PC, 0
header.

As a precaution, do make sure that you have set the same gamma for
your RGB *and* Gray working spaces and switch the "Use Dither" for
8-bit channel conversions to off. It should not matter when you load
the data as "raw" data, but just to make sure they don't interfere.

Bart

Kibo informs me that Mike Engles stated
that:

It does seem that what we have today is two types of digital imaging.
One is the truly scientific one that uses ALL linear data. The other is
a convenient engineering one that delivers the goods simply, by pre
compensating the linear data to display on non linear displays.

The difference is actaully quite simple. With photography, the intention
is to produce a final image that is as similar as possible to what a
human eye would've seen through the viewfinder, which requires a
non-linear response. With scientific imaging, OTOH, the interest is
generally in absolute data (eg; number of photons, detecting miniscule
light sources, etc), so there's no particular reason to try to
approximate the response of the human eye.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

Kibo informs me that Mike Engles stated
that:

It does seem that what we have today is two types of digital imaging.
One is the truly scientific one that uses ALL linear data. The other is
a convenient engineering one that delivers the goods simply, by pre
compensating the linear data to display on non linear displays.

The difference is actaully quite simple. With photography, the intention
is to produce a final image that is as similar as possible to what a
human eye would've seen through the viewfinder, which requires a
non-linear response. With scientific imaging, OTOH, the interest is
generally in absolute data (eg; number of photons, detecting miniscule
light sources, etc), so there's no particular reason to try to
approximate the response of the human eye.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

Bart van der Wolf wrote:

"Mike Engles" wrote in message
...
SNIP
Also why is image data from spacecraft and astronomy not
gamma encoded. It is after all digital photography.

Not necessarily. There is a difference between photometric data (e.g.
spectral reflection/absorption/emission in certain bands), and
pictorial imaging (e.g. stereo pairs in either visible light bands or
mixed with other spectral data).
One common issue between them is the desire to reduce quantization
errors (at least half of the LSB) to a minimum. Gamma encoding
provides a visually efficient encoding, but it can underutilize the
capacity at the lower, and overutilize (=additional quantization
errors) at the higher counts. Then there is the trade-off caused by
limited transmission bandwidth, and there is only so much one can do
with compression...

Bart


Hello

I would have thought that photographs taken by spacecraft are to be
viewed. They would be stored on the spacecraft in a file, prior to
relay. It strikes me that if gamma encoding is necessary for terrestrial
imaging to maximise the use of a limited number of bits, then that would
also apply to space photography. There was a thread in the scanner
group, where the expert consensus was that any imaging,storage and
processing in a linear domain invited image degradation and
posterisation. Yet we find that such linear imaging,storage and
processing is common in scientific digital imaging, where one would
imagine that extreme accuracy was paramount.

Do they use a large number of bits to avoid problems associated with
linear storage and processing? The expert consensus was that one would
need 18 to 20 bit linear images to match the efficiency of a 8 bit gamma
encoded image.

What is sauce for the goose is sauce for the gander.

Timo Autiokari has been saying for ages that scientific imaging was done
linearly. He has been abused soundly for his claims. We have been told
that no one who does serious image processing does it linearly. So all
the scientists of the world who regularly do their processing in a
linear domain are not really serious and that they are merely FADISTS
like Timo Autiokari.

Mike Engles