Digital BW, The Print

From: "johngeyles" <jge@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Monday, June 09, 2003 1:29 PM
Subject: [Digital BW] Re: Working in 8 bit then converting to 16 bit??


(snip earlier)
>
> I am purely speculating here ... but one can imagine an 8bit->16bit
> conversion that is not quite as straightforward and might create
> a better image.  The idea would be to make the hi-byte of the 16bit
> value equal to the 8bit value, and then put a random value into
> the low-byte.   This has the effect of reducing "mock bands" at the
> transitions between the 256 values; it is frequently used in
> computer image generation systems.  However, I'd be very surprised
> if Photoshop does this when you convert "mode" from 8bit to 16bit,
> in which case this wouldn't explain the supposed improvement from
> OPM when you give it 16bit images,
>

John,

As Roy says I doubt PS does this but it would perhaps make an interesting
tool or plug-in. Especially if you could control the width of the band and
apply it through a mask in PS. Perhaps even applying it after PS converts
from 8 to 16 bit. With 256 tones between each adjacent 8-bit tone converted
to 16-bit you have a lot of room to play with. You could even adjust the
distribution of random tones generated using different curve shapes.

I suspect that if you didn't control the amount and location of added tones
you would start to lose sharpness and resolution. Used well it might be a
great tool for smoothing out broad tonal transitions.

Martin Wesley

  ----- Original Message ----- 
  From: johngeyles 
  To: DigitalBlackandWhiteThePrint@yahoogroups.com 
  Sent: Monday, June 09, 2003 4:29 PM
  Subject: [Digital BW] Re: Working in 8 bit then converting to 16 bit??



  > 8 bit  to 16 bit conversion is so straightforward it's hard to
  > imagine why it would be better to do it before sending data to
  > OPM.   

  I am purely speculating here ... but one can imagine an 8bit->16bit
  conversion that is not quite as straightforward and might create
  a better image.  The idea would be to make the hi-byte of the 16bit
  value equal to the 8bit value, and then put a random value into
  the low-byte.   This has the effect of reducing "mock bands" at the
  transitions between the 256 values; it is frequently used in 
  computer image generation systems.  However, I'd be very surprised
  if Photoshop does this when you convert "mode" from 8bit to 16bit,
  in which case this wouldn't explain the supposed improvement from
  OPM when you give it 16bit images,

  John



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