And its like the anti-aliasing, smoothing and other stuff isn't being applied by the GDI+, which you can see in the image JJ posted, which is what I see as well. Might have to look at the include files to see if there is something not set correctly, maybe that's where the problem is. Normally with the code below it should apply all those:
Invoke GdipSetPixelOffsetMode, pGraphicsBuffer, PixelOffsetModeHighQuality
Invoke GdipSetPageUnit, pGraphicsBuffer, UnitPixel
Invoke GdipSetSmoothingMode, pGraphicsBuffer, SmoothingModeAntiAlias
Invoke GdipSetInterpolationMode, pGraphicsBuffer, InterpolationModeHighQualityBicubic