"Toby Thain" wrote in message
om...
wrote in message
. ..
In message ,
(Dave Martindale) wrote:

writes:

It's not obvious, though, when the missing values are 15-bit values.
Rather than 32,769 values, there are only about 11,000 values.

That is indeed very strange. I can't think of any reason the greyscale
representation should be any different from one channel of an RGB image.

Me neither. Just one of a series of many disappointments with PS. This
happens, I've found, with any conversion to greyscale in "16-bit" mode.
The color management is different for color and greyscale, too, so if
you switch back and forth there may be a continual loss of accuracy.

Someone should tell adobe that we have fast machines now and can work
with accurate data.

I've tried. Their engineer insists that it's 30x faster to work with
15 bit quantities than 16 bit ones.

--Toby

15bits gives you 5bits for R,G & B. There's no quality advantage between 15
vs. 16bits in terms of quality for RGB handling.

In article , Mike Engles
writes

Hello

Is astronomical image processing done in a linear space or a gamma
space?

Normally in linear space, Mike - because you are primarily interested in
physical quantities and their quantitative results.

After that has been achieved, the representation for human consumption
is created - either from the source data or the processed data depending
on the objective required.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)

In article , Mike Engles
writes

Hello

Is astronomical image processing done in a linear space or a gamma
space?

Normally in linear space, Mike - because you are primarily interested in
physical quantities and their quantitative results.

After that has been achieved, the representation for human consumption
is created - either from the source data or the processed data depending
on the objective required.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)

In article ,
wrote:

In message ,
(Mitch Alsup) wrote:

This looks like somebody is applying the gamma correction to the RAW data
ouptut = input**2.2 / some-fixed-scaling

No; it's totally linear. 6 sequential 16-bit values become one "PS
16-bit" value (except for the highest and lowest values, which are 3 to
1).

I think its time for Adobe to realize that people have fast machines,
and that they need to stop cutting corners on quality for speed.

We don't.

Without your original data to test, I can't even guess what went wrong.

But the 0..32768 representation will have to remain for the forseeable
future (unless you have a modern processor that does integer divides
just as fast as it does integer shifts).

Chris

In article ,
wrote:

In message ,
(Mitch Alsup) wrote:

This looks like somebody is applying the gamma correction to the RAW data
ouptut = input**2.2 / some-fixed-scaling

No; it's totally linear. 6 sequential 16-bit values become one "PS
16-bit" value (except for the highest and lowest values, which are 3 to
1).

I think its time for Adobe to realize that people have fast machines,
and that they need to stop cutting corners on quality for speed.

We don't.

Without your original data to test, I can't even guess what went wrong.

But the 0..32768 representation will have to remain for the forseeable
future (unless you have a modern processor that does integer divides
just as fast as it does integer shifts).

Chris

In article , Toby
Thain wrote:

wrote in message
. ..
In message ,
(Dave Martindale) wrote:

writes:

It's not obvious, though, when the missing values are 15-bit values.
Rather than 32,769 values, there are only about 11,000 values.

That is indeed very strange. I can't think of any reason the greyscale
representation should be any different from one channel of an RGB image.

Me neither. Just one of a series of many disappointments with PS. This
happens, I've found, with any conversion to greyscale in "16-bit" mode.
The color management is different for color and greyscale, too, so if
you switch back and forth there may be a continual loss of accuracy.

Someone should tell adobe that we have fast machines now and can work
with accurate data.

Photoshop is accurate, as far as we know.
Without your original data to test, I don't know what might have gone
wrong. But other people who are picky about their bits don't have any
problems with Photoshop.


I've tried. Their engineer insists that it's 30x faster to work with
15 bit quantities than 16 bit ones.

Which is correct (for 0..32768 representation versus 0..65535
representation).

Chris

In article , Toby
Thain wrote:

wrote in message
. ..
In message ,
(Dave Martindale) wrote:

writes:

It's not obvious, though, when the missing values are 15-bit values.
Rather than 32,769 values, there are only about 11,000 values.

That is indeed very strange. I can't think of any reason the greyscale
representation should be any different from one channel of an RGB image.

Me neither. Just one of a series of many disappointments with PS. This
happens, I've found, with any conversion to greyscale in "16-bit" mode.
The color management is different for color and greyscale, too, so if
you switch back and forth there may be a continual loss of accuracy.

Someone should tell adobe that we have fast machines now and can work
with accurate data.

Photoshop is accurate, as far as we know.
Without your original data to test, I don't know what might have gone
wrong. But other people who are picky about their bits don't have any
problems with Photoshop.


I've tried. Their engineer insists that it's 30x faster to work with
15 bit quantities than 16 bit ones.

Which is correct (for 0..32768 representation versus 0..65535
representation).

Chris