From kde-kimageshop  Sun Oct 23 19:06:23 2005
From: Boudewijn Rempt <boud () valdyas ! org>
Date: Sun, 23 Oct 2005 19:06:23 +0000
To: kde-kimageshop
Subject: Inversion in colorspaces
Message-Id: <200510232106.26669.boud () valdyas ! org>
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This turns out to be quite a fun topic... I haven't got it working complete=
ly.=20
16-bit rgba works perfectly, but, for 8-bit rgb, I get a blank image back i=
f=20
I go through xyz (I will add an optimized 8-bit rgb function later, but thi=
s=20
is for testing). I'm not sure why, maybe someone else has an idea. This is=
=20
the code:

void KisAbstractColorSpace::invertColor(Q_UINT8 * src, Q_INT32 nPixels)
{
    if ( m_defaultToXYZ !=3D 0 && m_defaultFromXYZ !=3D 0 ) {
        KisColorSpace * xyz =3D m_parent->getXYZ16();
       =20
        Q_UINT32 psize =3D xyz->pixelSize();

        if ( m_conversionCache.size() < nPixels * psize ) {
            m_conversionCache.resize( nPixels * psize, QGArray::SpeedOptim =
);
        }

        cmsDoTransform( m_defaultToXYZ, const_cast<Q_UINT8*>( src ),=20
m_conversionCache.data(), nPixels);
        xyz->invertColor(m_conversionCache.data(), nPixels);
        cmsDoTransform( m_defaultFromXYZ, m_conversionCache.data(),=20
const_cast<Q_UINT8*>( src ), nPixels);
    }
    else {
	...
    }
}

The transforms to and back XYZ work, I tested that by commenting out the ca=
ll=20
to xyz->invertColor().=20

void KisXyzColorSpace::invertColor(Q_UINT8 * src, Q_INT32 nPixels)
{
    Q_INT32 pSize =3D pixelSize();
   =20
    while (nPixels--)
    {
        Q_UINT16 * p =3D reinterpret_cast<Q_UINT16 *>(src);
        p[PIXEL_X] =3D UINT16_MAX - p[PIXEL_X];
        p[PIXEL_Y] =3D UINT16_MAX - p[PIXEL_Y];
        p[PIXEL_Z] =3D UINT16_MAX - p[PIXEL_Z];
        src +=3D pSize;
    }
}

An example of the xyz values before and after inverting:

krita: Before X 2860, Y 3377, z 2426
krita: After X 62675, Y 62158, z 63109

Looks good, so everything should work... But it doesnt :-(.

Anyway, there's also the intriguing mention of building an inversion lut in=
=20
the lcms documentation, but I don't understand it at all... Perhaps Casper=
=20
can take a look at that?


=2D-=20
Boudewijn Rempt=20
http://www.valdyas.org/fading/index.cgi

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