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"16-bit" mode.



 
 
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  #34  
Old November 17th 04, 11:34 PM
external usenet poster
 
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Default

In message ,
"Bart van der Wolf" wrote:

"Mike Engles" wrote in message
...
SNIP
There was a discussion about this kind of thing on the scanner

group,
comp.periphs.scanner. Post your observation there. You might get a
explanation.


You probably are referring to these:
1. Chris Cox's 'explanation' of the internal format of 15bits+1:
http://groups.google.nl/groups?selm=...25ccox%40minds
pring.com&output=gplain
2. The way Photoshop converts (16-bits to 8-bits)
http://groups.google.com/groups?selm...%25ccox%40mind
spring.com&output=gplain


The slight gamma turned out to be from color management, but what I am
talking about appears to be slightly different from what is discussed in
the 15-bit + 1, or 16-8-bit discussions. 16-bit greyscale is highly
posterized. With color management turned off, the count starts:

0 0 0 1 1 1 1 1 1 3 3 3 3 3 3 ...


Where is 2? You can't be skipping numbers while others are being
repeated multiple times; that makes no sense whatsoever.

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.
--


John P Sheehy

  #35  
Old November 17th 04, 11:34 PM
external usenet poster
 
Posts: n/a
Default

In message ,
"Bart van der Wolf" wrote:

"Mike Engles" wrote in message
...
SNIP
There was a discussion about this kind of thing on the scanner

group,
comp.periphs.scanner. Post your observation there. You might get a
explanation.


You probably are referring to these:
1. Chris Cox's 'explanation' of the internal format of 15bits+1:
http://groups.google.nl/groups?selm=...25ccox%40minds
pring.com&output=gplain
2. The way Photoshop converts (16-bits to 8-bits)
http://groups.google.com/groups?selm...%25ccox%40mind
spring.com&output=gplain


The slight gamma turned out to be from color management, but what I am
talking about appears to be slightly different from what is discussed in
the 15-bit + 1, or 16-8-bit discussions. 16-bit greyscale is highly
posterized. With color management turned off, the count starts:

0 0 0 1 1 1 1 1 1 3 3 3 3 3 3 ...


Where is 2? You can't be skipping numbers while others are being
repeated multiple times; that makes no sense whatsoever.

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.
--


John P Sheehy

  #36  
Old November 18th 04, 12:07 AM
external usenet poster
 
Posts: n/a
Default

In message ,
"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)"?

where PS = the photoshop "16-bit" value and
IP = the 16-bit output from ImagesPlus.


--


John P Sheehy

  #37  
Old November 18th 04, 12:07 AM
external usenet poster
 
Posts: n/a
Default

In message ,
"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)"?

where PS = the photoshop "16-bit" value and
IP = the 16-bit output from ImagesPlus.


--


John P Sheehy

  #38  
Old November 18th 04, 05:29 AM
Roger N. Clark (change username to rnclark)
external usenet poster
 
Posts: n/a
Default

wrote:

In message ,
"Bart van der Wolf" wrote:


"Mike Engles" wrote in message
...
SNIP

There was a discussion about this kind of thing on the scanner


group,

comp.periphs.scanner. Post your observation there. You might get a
explanation.


You probably are referring to these:
1. Chris Cox's 'explanation' of the internal format of 15bits+1:
http://groups.google.nl/groups?selm=...25ccox%40minds
pring.com&output=gplain
2. The way Photoshop converts (16-bits to 8-bits)
http://groups.google.com/groups?selm...%25ccox%40mind
spring.com&output=gplain



The slight gamma turned out to be from color management, but what I am
talking about appears to be slightly different from what is discussed in
the 15-bit + 1, or 16-8-bit discussions. 16-bit greyscale is highly
posterized. With color management turned off, the count starts:

0 0 0 1 1 1 1 1 1 3 3 3 3 3 3 ...


Where is 2? You can't be skipping numbers while others are being
repeated multiple times; that makes no sense whatsoever.

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.


John:
Can you send me your 256*256 raw file? I'll take a look at it
with my tools, including some custom image processing
unix programs and compare to photoshop and ImagesPlus.

Roger

  #39  
Old November 18th 04, 05:29 AM
Roger N. Clark (change username to rnclark)
external usenet poster
 
Posts: n/a
Default

wrote:

In message ,
"Bart van der Wolf" wrote:


"Mike Engles" wrote in message
...
SNIP

There was a discussion about this kind of thing on the scanner


group,

comp.periphs.scanner. Post your observation there. You might get a
explanation.


You probably are referring to these:
1. Chris Cox's 'explanation' of the internal format of 15bits+1:
http://groups.google.nl/groups?selm=...25ccox%40minds
pring.com&output=gplain
2. The way Photoshop converts (16-bits to 8-bits)
http://groups.google.com/groups?selm...%25ccox%40mind
spring.com&output=gplain



The slight gamma turned out to be from color management, but what I am
talking about appears to be slightly different from what is discussed in
the 15-bit + 1, or 16-8-bit discussions. 16-bit greyscale is highly
posterized. With color management turned off, the count starts:

0 0 0 1 1 1 1 1 1 3 3 3 3 3 3 ...


Where is 2? You can't be skipping numbers while others are being
repeated multiple times; that makes no sense whatsoever.

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.


John:
Can you send me your 256*256 raw file? I'll take a look at it
with my tools, including some custom image processing
unix programs and compare to photoshop and ImagesPlus.

Roger

 




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