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-   -   "16-bit" mode. (http://www.photobanter.com/showthread.php?t=19356)

Toby Thain November 18th 04 06:59 PM
wrote in message . ..
...
The sad fact of the matter is that not only is PS' "16-bit" RGB only
15-bit, but its "16-bit" greyscale has even less effective bits. Even
if you perform a bicubic upsampling, you can't get the missing values.

That's kind of obvious once you accept that the internal
representation is only 15 bits.

[email protected] November 18th 04 09:59 PM
In message ,
(Toby Thain) wrote:

wrote in message . ..
...
The sad fact of the matter is that not only is PS' "16-bit" RGB only
15-bit, but its "16-bit" greyscale has even less effective bits. Even
if you perform a bicubic upsampling, you can't get the missing values.

That's kind of obvious once you accept that the internal
representation is only 15 bits.

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.
--


John P Sheehy


[email protected] November 18th 04 09:59 PM
In message ,
(Toby Thain) wrote:

wrote in message . ..
...
The sad fact of the matter is that not only is PS' "16-bit" RGB only
15-bit, but its "16-bit" greyscale has even less effective bits. Even
if you perform a bicubic upsampling, you can't get the missing values.

That's kind of obvious once you accept that the internal
representation is only 15 bits.

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.
--


John P Sheehy


Dave Martindale November 19th 04 04:44 AM
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.

Dave

Dave Martindale November 19th 04 04:44 AM
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.

Dave

[email protected] November 19th 04 11:41 AM
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.
--


John P Sheehy


[email protected] November 19th 04 11:41 AM
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.
--


John P Sheehy


[email protected] November 19th 04 07:06 PM
wrote:

"Roger N. Clark (change username to rnclark)"
wrote:

In my testing of photoshop on real images, I find the following
equation:

PS = int(IP/2),

Are you sure it isn't "PS = int((IP+1)/2)"?

A minor danger is that if IP is 0xffff, the above will map to 0 if
done in 16b arithmetic. "IP 1" (M. Clarke's equation) is a single
instruction that doesn't suffer from overflow problems. But if wider
arithmetic is allowed, then:

PS = rint(IP*(32768.0/65535.0))

or its integer equivalent may be used.

Note that PhotoSlop is "just an image editor" (a large, complicated,
extensible, useful one to be sure), so precise stuff like you are
demanding will probably never make it high on the priority list at
Adobe, where most of their users are graphic artists, not by-the-bit
technician types. Can MaximDL and similar handle non-astronomical
imagery? It's internals are probably _alot_ more formal (linear
images, etc).

[email protected] November 19th 04 07:06 PM
wrote:

"Roger N. Clark (change username to rnclark)"
wrote:

In my testing of photoshop on real images, I find the following
equation:

PS = int(IP/2),

Are you sure it isn't "PS = int((IP+1)/2)"?

A minor danger is that if IP is 0xffff, the above will map to 0 if
done in 16b arithmetic. "IP 1" (M. Clarke's equation) is a single
instruction that doesn't suffer from overflow problems. But if wider
arithmetic is allowed, then:

PS = rint(IP*(32768.0/65535.0))

or its integer equivalent may be used.

Note that PhotoSlop is "just an image editor" (a large, complicated,
extensible, useful one to be sure), so precise stuff like you are
demanding will probably never make it high on the priority list at
Adobe, where most of their users are graphic artists, not by-the-bit
technician types. Can MaximDL and similar handle non-astronomical
imagery? It's internals are probably _alot_ more formal (linear
images, etc).

Toby Thain November 19th 04 07:22 PM
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


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