Re: [Lcms-user] How to convert RGB in some ICC profile to LAB

[<ma...@li...>]

Hi,

>I found in description of sRGB matrix which convert sRGB to XYZ and in
>your source is method how to convert XYZ to LAB. Is it good solution?
>Because I don't want to distribute these big ICC profiles with my
>application.

The matrix is not enought, since sRGB needs a gamma linear interpolation too.
Of course you can do the conversion process "by hand", but
is long and tedious, there are precission issues involved and is easy to
make mistakes. Also, without 3D interpolation  it will be very slow, and
I guess it is not worth all the work it deserves.

I agree lcmsxyzi.icm and lcmslabi.icm are too big. If you can wait just a bit,
ver 1.08 is expected to be released on summer's end (middle september).
New ver. adds the creation of sRGB, Lab and XYZ profiles "on fly", and other
major features, like scanner profile generation. The API remains same, so you
can experiment with the actual profiles, and all then change, humm.. say,
"cmsOpenProfileFromFile()" to "cmsCreateLabProfile()" when 1.08 were
available.

Marti.





----- Original Message -----
From: "Boris Letocha" <b.l...@gm...>
To: "Martí Maria" <ma...@li...>
Cc: <lcm...@li...>
Sent: Wednesday, August 08, 2001 9:50 AM
Subject: RE: [Lcms-user] How to convert RGB in some ICC profile to LAB


First thanks for answer.

I found in description of sRGB matrix which convert sRGB to XYZ and in
your source is method how to convert XYZ to LAB. Is it good solution?
Because I don't want to distribute these big ICC profiles with my
application.

BTW in libmng I found function how to create sRGB profile in memory so
it is IMHO good to include this function in lcms API also.

Boris Letocha

> -----Original Message-----
> From: Martí Maria [mailto:ma...@li...]
> Sent: Wednesday, August 08, 2001 8:08 PM
> To: Boris Letocha
> Cc: lcm...@li...
> Subject: Re: [Lcms-user] How to convert RGB in some ICC profile to LAB
>
>
> Hi,
>
> You need to use lcmslabi.icm or lcmsxyzi.icm as
> output profile. I do attach a sample on how to do
> the whole thing.
>
> Martí Maria
> The little cms project
> http://www.littlecms.com
> ma...@li...
>
>
> ----- Original Message -----
> From: "Boris Letocha" <b.l...@gm...>
> To: <lcm...@li...>
> Sent: Wednesday, August 08, 2001 8:18 AM
> Subject: [Lcms-user] How to convert RGB in some ICC profile to LAB
>
>
> I really searched hard, but cannot find such API function in lcms.
>
> Easier can be how to convert sRGB to Lab or XYZ colorspace.
>
> Thanks for any help.
>
> Boris Letocha
>
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