I'm an old fashioned pixel pusher so want to use the "sRGB built-in" colourspace for a traditional, naive colour intensity curve, however using posterize with "sRGB built-in" result in unequal segmentation.

I can get equal segmentation using the default colourspace, but then don't get the colour intensity curve I desire.

It appears to me as though the posterize is operating in a linearized colourspace, regardless of image colourspace.

Is there any way I can make it operate in my chosen colourspace?

Oh, that's actually kind of interesting... Posterize works in 16 bits sRGB, and was written before 16 bits sRGB used a linear TRC by default, so, yes, it works in linear space, unintentionally.

Should be fixed in https://invent.kde.org/kde/krita/commit ... b871d02706

Cheers, that's working as I was wanting.

Actually, I'm getting some serious slowdown with a posterize filter layer now.

Speed is back to normal if I revert this commit.

That's quite possible, because we're now not reusing the global color transformations, but recreate them especially for the posterize filter.

I hackily moved the colour transformation creation out of the transform function into the constructor and filter layers are working at interactive speeds again.

please share the patch? I might just be prepared to apply it

Never created a patch before so might be screwy.

Code: Select all

diff --git a/plugins/filters/posterize/posterize.cpp b/plugins/filters/posterize/posterize.cpp
index b9ecff442a..776371e996 100644
--- a/plugins/filters/posterize/posterize.cpp
+++ b/plugins/filters/posterize/posterize.cpp
@@ -68,6 +68,22 @@ KisPosterizeColorTransformation::KisPosterizeColorTransformation(int steps, cons
 {
     m_step = KoColorSpaceMathsTraits<quint16>::max / steps;
     m_halfStep = m_step / 2;
+    m_fromConversion = KoColorSpaceRegistry::instance()->createColorConverter(
+        m_colorSpace,
+        KoColorSpaceRegistry::instance()->rgb16("sRGB-elle-V2-srgbtrc.icc"),
+        KoColorConversionTransformation::internalRenderingIntent(),
+        KoColorConversionTransformation::internalConversionFlags());
+    m_toConversion = KoColorSpaceRegistry::instance()->createColorConverter(
+        KoColorSpaceRegistry::instance()->rgb16("sRGB-elle-V2-srgbtrc.icc"),
+        m_colorSpace,
+        KoColorConversionTransformation::internalRenderingIntent(),
+        KoColorConversionTransformation::internalConversionFlags());
+}
+
+KisPosterizeColorTransformation::~KisPosterizeColorTransformation()
+{
+    delete m_fromConversion;
+    delete m_toConversion;
 }
 
 KisConfigWidget* KisFilterPosterize::createConfigurationWidget(QWidget* parent, const KisPaintDeviceSP dev, bool) const
@@ -89,20 +105,9 @@ void KisPosterizeColorTransformation::transform(const quint8* src, quint8* dst,
 {
     quint16 m_rgba[4];
     quint16 m_mod[4];
-    KoColorConversionTransformation* t =
-            KoColorSpaceRegistry::instance()->createColorConverter(m_colorSpace,
-                                                                   KoColorSpaceRegistry::instance()->rgb16("sRGB-elle-V2-srgbtrc.icc"),
-                                                                   KoColorConversionTransformation::internalRenderingIntent(),
-                                                                   KoColorConversionTransformation::internalConversionFlags());
-    KoColorConversionTransformation* b =
-            KoColorSpaceRegistry::instance()->createColorConverter(
-                KoColorSpaceRegistry::instance()->rgb16("sRGB-elle-V2-srgbtrc.icc"),
-                m_colorSpace,
-                KoColorConversionTransformation::internalRenderingIntent(),
-                KoColorConversionTransformation::internalConversionFlags());
 
     while (nPixels--) {
-        t->transform(src, reinterpret_cast<quint8 *>(m_rgba), 1);
+        m_fromConversion->transform(src, reinterpret_cast<quint8 *>(m_rgba), 1);
 
         m_mod[0] = m_rgba[0] % m_step;
         m_mod[1] = m_rgba[1] % m_step;
@@ -114,7 +119,7 @@ void KisPosterizeColorTransformation::transform(const quint8* src, quint8* dst,
         m_rgba[2] = m_rgba[2] + (m_mod[2] > m_halfStep ? m_step - m_mod[2] : -m_mod[2]);
         m_rgba[3] = m_rgba[3] + (m_mod[3] > m_halfStep ? m_step - m_mod[3] : -m_mod[3]);
 
-        b->transform(reinterpret_cast<quint8 *>(m_rgba), dst, 1);
+        m_toConversion->transform(reinterpret_cast<quint8 *>(m_rgba), dst, 1);
         src += m_psize;
         dst += m_psize;
     }
diff --git a/plugins/filters/posterize/posterize.h b/plugins/filters/posterize/posterize.h
index 88f7b69922..2774a94d33 100644
--- a/plugins/filters/posterize/posterize.h
+++ b/plugins/filters/posterize/posterize.h
@@ -50,12 +50,15 @@ class KisPosterizeColorTransformation : public KoColorTransformation
 {
 public:
     KisPosterizeColorTransformation(int steps, const KoColorSpace* cs);
+    ~KisPosterizeColorTransformation() override;
     void transform(const quint8* src, quint8* dst, qint32 nPixels) const override;
 private:
     const KoColorSpace* m_colorSpace;
     quint32 m_psize;
     quint16 m_step;
     quint16 m_halfStep;
+    KoColorConversionTransformation* m_fromConversion;
+    KoColorConversionTransformation* m_toConversion;
 };
 
 #endif


Added patch to phabricator here: https://phabricator.kde.org/D21529