swscaler methods recommendation & artifact types

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@6686 b3059339-0415-0410-9bf9-f77b7e298cf2

DOCS/tech/swscaler_methods.txt

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+
+artifact types:
+---------------------------------------------------------------------
+ringing
+	wave or noise like patterns around sharp edges
+	bad: sinc, lanczos (with high filter length)
+	acceptable: lanczos (with low filter length), cubic, spline
+	ok: area, (fast)blinear, gauss, point
+
+blur
+	loss of detail / high frequency
+	bad: gauss with high variance
+	acceptable: (fast)bilinear, area
+	ok: others
+
+aliassing (only downscale)
+	straight lines look like staircases
+	areas of high detail look worse
+	regular patterns turn into a funny looking mess (moire patterns)
+	bad: fast bilinear, point, gauss with low variance
+	acceptable: area
+	ok: others
+
+blocky (upscale only)
+	looks like the image is made of rectangular blocks like a mosaic
+	bad: point
+	ok: others
+
+recommanditions: (based upon my personal oppinion many ppl might disagree ...)
+---------------------------------------------------------------------
+        
+the recomanded scalers for upscaling:
+fast_bilinear, point if speed is important
+cubic, spline, lanczos if quality is important
+
+the recomanded scalers for downscaling:
+fast_bilinear, point if speed is important
+gauss, bilinear if quality is important
+cubic, spline, lanczos if a sharper picture is important
+
+note: when encoding at a limited amount of bits (not constant quantizer) 
+than a slightly blured input might look better after decoding than a slightly 
+sharpend one, especially for lower bitrates
+
+sws numbers / names / artefact types
+-------------------------------------------------------------------------
+r ringing
+b blurry
+a aliasing (downscale only)
+m mosaic (blocky) (upscale only)
+
+-sws 0	fast bilinear			 bA
+-sws 1	bilinear			 b
+-sws 2	bicubic	high sharpness		r
+		low sharpness		 b
+-sws 3	experimental			????
+-sws 4	nearest neighbour		  AM
+-sws 5	area				 ba
+-sws 6	luma bicubic / chroma bilinear	r
+-sws 7	gauss	low sharpness		 B
+		high sharpness		  AM
+-sws 8	sinc				R
+-sws 9	lanczos	long filter		R
+		short filter		 b
+-sws 10	bicubic spline			r
+
+Notes: 
+	area upscale is identical to bilinear