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Re: [csswg-drafts] [css-color-4] Transfer function for ProPhoto RGB (#5229)

From: Chris Lilley via GitHub <sysbot+gh@w3.org>
Date: Wed, 17 Jun 2020 14:06:21 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-645395507-1592402780-sysbot+gh@w3.org>
From the Kodak whitepaper:

> One  potential  use  of  the  ROMM RGB  color  space  is  as  a  working  color  space  for Adobe Photoshop software.  However, it should be noted that Adobe Photoshop software currently limits the nonlinearity that can be used to define a valid working space **to be a simple  gamma  function**.  However,  both  the  Adobe  Photoshop  software  implementation,as  well  as  the  Kodak  Color  Matching  Module  (CMM)  implementation  automatically impose  a  “slope  limit”  of  16  at  the  dark  end  of  the  tone scale.  Although  a  profile  that explicitly  incorporates  the  nonlinearity  with  the  slope  limit  can  not  be  used  by  Adobe Photoshop  software,  a  profile  using  a  simple  gamma  function  nonlinearity  produces  the net effect of Eq. (2) when used by Adobe Photoshop software or the current version of the Kodak CMM. Therefore, to ensure Adobe Photoshop software compatibility, the ROMM RGB  ICC  profile  created  by  Eastman  Kodak  Company  uses  a  simple  gamma  function nonlinearity without the slope limit, rather than the form shown in Eq. (2). At some point in the future it may be possible to produce a new ICC profile that explicitly incorporates the slope limit if Adobe were to modify the Photoshop software software to remove this artificial  restriction.    Although  this  would  not  have  any  effect  on  the  results  obtained using  Adobe  Photoshop  software  or  the  Kodak  CMM,  it  would  increase  the  likelihood that  equivalent  results  would  be  obtained  using  different  CMMs  that  may  or  may  not include the same slope limiting feature

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