[Lcms-user] Re: How can I .....

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

Ciao Bernardo,

> What can I do to obtain  in the OutputBuffer the Lab value?

Just use lcmslabi.icm (present on distribution packages) as output =
profile.
For converting from/to floating point, you have the routines in =
lcmsapi.txt,
here I reproduce...

----------------------------------
// Convert L to double

double L2float(WORD v)
{
       Fixed32 fix32;

       fix32 =3D (Fixed32) v;
       return (double) fix32 / 652.800;
}


// the a/b part

double ab2float(WORD v)
{
       Fixed32 fix32;


       fix32 =3D (Fixed32) v;
       return ((double) fix32/256.0)-128.0;
}
---------------------------------------

Then, your code will be something like... (please note I'm using 16 bits =
Lab,  TYPE_Lab_16)

| WORD Output[3]
| hOutputProfile =3D cmsOpenProfileFormFile("lcmslabi.icm", "r");
| cmsHTRANSFORM hTransform =3D  cmsCreateTrasform (hInputProfile,  =
TYPE_RGB_8,
|                                                                        =
                   hOutputProfile, TYPE_Lab_16,
|                                                                        =
                    INTENT_PERCEPTUAL, 0)                                =
                            | ...                        =20

 Translating 1 pixel=20

|  cmsDoTransform(hTransform, InputBuffer, OutputBuffer, 1)
|  L =3D L2Float(Output[0]);
|  a =3D ab2Float(Output[1]);
|  b =3D ab2Float(Output[2]);                   =20

Hope this helps.

Mart=ED Maria
The little cms project
http://www.littlecms.com
ma...@li...


----- Original Message -----=20
From: "Bernardo Pucci" <cyb...@ti...>
To: <in...@li...>
Sent: Saturday, June 09, 2001 3:46 PM
Subject: How can I .....


> Hi littlecms stuff,
> I'm an Italian student and I use the littlecms engine to obtain  color =
space
> conversion.
> No problem happen If  I trasform an image (RGB buffer) between 2 icc
> profiles (INPUT and DISPLAY), but I don't understand how I can obtain =
a Lab
> buffer from an RGB buffer with the use of an INPUT profile only.
> I must have Lab value for metrics size and I use an INPUT (digital
> fotocamera) icc profile with color space RGB and connection space Lab.
> The problem occurs (segmentation fault) when trasform is create:
>=20
> cmsHTRANSFORM hTransform =3D  cmsCreate Trasform (hInputProfile, =
TYPE_RGB_8,
> NULL, TYPE_Lab_8,
>=20
> INTENT_PERCEPTUAL, 0);
> What can I do to obtain  in the OutputBuffer the Lab value?
>=20
> I have define:
> unsigned char InputBuffer    for RGB value
> float OutputBuffer     for Lab value.
>=20
> In hoping for a reply thanks
> Pucci Bernardo
>=20
>=20
>=20