Re: [Lcms-user] proofing lcms vs photoshop

[H. H. <hh...@gm...>]

thanks for your answer, marti.

with "ink black" checked it does indeed look like the photoshop 
output.

however, i spoke again to our "printer-guys" and they do NOT have that 
checked in photoshop. they use the INTENT_PERECPTUAL and the only 
other thing checked is the blackpoint compensation.

as you said, the lcms output is like the "ink black" setting in 
photoshop. since we are not using that setting, i am wondering how can 
i disable that default setting in lcms?

regards, h



On Fri, 28 May 2004 12:01:47 +0200, Marti Maria wrote:
>
> Hi,
>
>> i am seeing a clear difference between proofing in photoshop
>> compared
>> to lcms.
>
> Ok, there are a few settings to adjust. First, lcms allows proofing
> intent, which
> must me set to relative colorimetric to mimic photoshop (tifficc
> toggle -m1)
> And then, photoshop has "paper white", "black ink" and "preserve
> numbers".
>
> The softproofing done by lcms is same as you were using "black ink"
> only.
> This should give you practically same results as photoshop in all
> but absolute
> colorimetric intent.  There is a bug in that latter, which has
> passed unnoticed
> because this combination is rarely used. To fix it, add following
> lines at the
> very beginning of _cmsComputeSoftProofLUT (file is cmsgmt.c)
>
> if (nIntent =3D=3D INTENT_ABSOLUTE_COLORIMETRIC)
> nIntent =3D INTENT_RELATIVE_COLORIMETRIC;
>
> I will incorporate this change in next revision, but not in 1.13
> because
> obvious reasons.
>
> lcms, as photoshop, does not rely on preview tags, since most
> profiles
> have this information broken. Instead, it computes the preview on
> its own,
> using the AToBx/BToAx tags.
>
> Regards,
> Marti Maria
> The little cms project
> http://www.littlecms.com
>
> ----- Original Message -----
> From: H. Holtij
> To: lcm...@li...
> Sent: Wednesday, May 26, 2004 1:13 PM
> Subject: [Lcms-user] proofing lcms vs photoshop
>
>
> hi,
>
> i am seeing a clear difference between proofing in photoshop
> compared
> to lcms.
> i have a tif image (TYPE_BGRA_8) and i want to proof it with a
> printer
> profile. the image has no profile attached, so i am using the
> standard
> sRGB. output device is my monitor so i am using the appropriate
> profile for it (profile is setup in winxp).
>
> i wrote the following short code snippet to test the proofing with
> lcms:
>
>
> cmsHPROFILE hInProfile=3DNULL, hOutProfile=3DNULL, hProofProfile=3DNULL;
> cmsHTRANSFORM hTransform;
> int i;
>
> char*        pszPrint =3D
> "C:\\WINDOWS\\system32\\spool\\drivers\\color\\7600
> RGB Enhanced Matte 720.icm";
> char*        pszP1 =3D
> "C:\\WINDOWS\\system32\\spool\\drivers\\color\\sRGB
> Color Space Profile.icm";
> char*        pszP2 =3D
> "C:\\WINDOWS\\system32\\spool\\drivers\\color\\VG191b.ICM";
>
>
> //        hInProfile  =3D cmsOpenProfileFromFile( pszP1, "r" );
> hInProfile =3D cmsCreate_sRGBProfile();
>
> hOutProfile =3D cmsOpenProfileFromFile( pszP2, "r" );
> //        hOutProfile =3D cmsCreate_sRGBProfile();
>
> hProofProfile =3D cmsOpenProfileFromFile( pszPrint, "r" );
>
>
> DWORD type =3D TYPE_BGRA_8;
>
> hTransform =3D cmsCreateProofingTransform( hInProfile, type,
> hOutProfile, type, hProofProfile, INTENT_ABSOLUTE_COLORIMETRIC,
> INTENT_ABSOLUTE_COLORIMETRIC, cmsFLAGS_SOFTPROOFING );
>
> for( i=3D0; i < img2.GetHeight(); i++)
> {
> BYTE*        pIn =3D  img1.GetBits() + i * img1.GetBytesPerLine();
> BYTE*        pOut =3D img2.GetBits() + i * img2.GetBytesPerLine();
> cmsDoTransform( hTransform, pIn, pOut, img1.GetWidth() );
> }
>
> cmsDeleteTransform( hTransform );
> if( hInProfile )        cmsCloseProfile( hInProfile );
> if( hOutProfile )        cmsCloseProfile( hOutProfile );
> if( hProofProfile )        cmsCloseProfile( hProofProfile );
>
>
> i tried sRGB as output profile as well, but there was (as expected)
> only a minimal difference.
>
> in photoshop i am doing the same. i use the same 7600 profile as
> proof
> profile and have the intent set to PERCEPTUAL. but the
> photoshop display looks very different.
>
> i just installed lcms today, so i guess i must be missing something?
>
> i tried basically every permutation of intents but none of those
> combinations came really close to the photoshop display...
>
> i understand that one of the preview tags must be set for soft
> proofing to work.
> however, in the profile i am using none of them are set. i
> downloaded a few more profiles for this printer and NONE of them
> had any
> of the three preview tags set.
>
> how does photoshop do the proofing without these tags?
> how can i do the same using lcms?
>
>
> btw, marti:
> BIG THANKS to you for implementing this lib the way you did it
> (clear
> structure, great API), and especially for making it open source!!
> i also noticed that you (and others) really take your time to
> answer the posts here
> very patiently. THUMBS UP!
>
> all the best,
> harald