Improve colorspace conversion.

Choose sws flags based on what conversion is being done.

src/modules/avformat/common.c

@@ -20,9 +20,65 @@
 #include "common.h"
 
 #include <libavutil/channel_layout.h>
+#include <libavutil/pixdesc.h>
 #include <libavutil/samplefmt.h>
 
-int mlt_default_sws_flags = SWS_BICUBIC | SWS_FULL_CHR_H_INP | SWS_FULL_CHR_H_INT | SWS_ACCURATE_RND;
+int get_sws_flags(int srcwidth, int srcheight, int srcformat, int dstwidth, int dstheight, int dstformat)
+{
+	// Use default flags unless there is a reason to use something different.
+	int flags = SWS_BICUBIC | SWS_FULL_CHR_H_INP | SWS_FULL_CHR_H_INT | SWS_ACCURATE_RND;
+
+	if( srcwidth != dstwidth || srcheight != dstheight )
+	{
+		// Any resolution change should use default flags
+		return flags;
+	}
+
+	const AVPixFmtDescriptor* srcDesc = av_pix_fmt_desc_get(srcformat);
+	const AVPixFmtDescriptor* dstDesc = av_pix_fmt_desc_get(dstformat);
+
+	if( !srcDesc || !dstDesc )
+	{
+		return flags;
+	}
+
+	if( (srcDesc->flags & AV_PIX_FMT_FLAG_RGB) != 0 &&
+		(dstDesc->flags & AV_PIX_FMT_FLAG_RGB) == 0)
+	{
+		// RGB -> YUV
+		flags = SWS_BICUBIC;
+		flags |=  SWS_ACCURATE_RND;   // Can improve precision by one bit
+		flags |=  SWS_FULL_CHR_H_INT; // Avoids luma reduction. Causes chroma bleeding when used with SWS_BICUBIC
+	}
+	else if( (srcDesc->flags & AV_PIX_FMT_FLAG_RGB) == 0 &&
+			(dstDesc->flags & AV_PIX_FMT_FLAG_RGB) != 0)
+	{
+		// YUV -> RGB
+		// Going from lower sampling to full sampling - so pick the closest sample without interpolation
+		flags = SWS_POINT;
+		flags |=  SWS_ACCURATE_RND;   // Can improve precision by one bit
+		flags |=  SWS_FULL_CHR_H_INT; // Avoids luma reduction. Does not cause chroma bleeding when used with SWS_POINT
+	}
+	else if( (srcDesc->flags & AV_PIX_FMT_FLAG_RGB) == 0 &&
+			(dstDesc->flags & AV_PIX_FMT_FLAG_RGB) == 0)
+	{
+		// YUV -> YUV
+		if( srcDesc->log2_chroma_w == dstDesc->log2_chroma_w &&
+			srcDesc->log2_chroma_h == dstDesc->log2_chroma_h )
+		{
+			// No chroma subsampling conversion. No interpolation required
+			flags = SWS_POINT;
+			flags |=  SWS_ACCURATE_RND; // Can improve precision by one bit
+		}
+		else
+		{
+			// Chroma will be interpolated. Bilinear is suitable.
+			flags = SWS_FAST_BILINEAR | SWS_ACCURATE_RND;
+		}
+	}
+
+	return flags;
+}
 
 int mlt_to_av_sample_format( mlt_audio_format format )
 {

src/modules/avformat/common.h

@@ -29,6 +29,6 @@ mlt_channel_layout av_channel_layout_to_mlt( int64_t layout );
 mlt_channel_layout mlt_get_channel_layout_or_default( const char* name, int channels );
 int mlt_set_luma_transfer( struct SwsContext *context, int src_colorspace,
 	int dst_colorspace, int src_full_range, int dst_full_range );
-extern int mlt_default_sws_flags;
+int get_sws_flags(int srcwidth, int srcheight, int srcformat, int dstwidth, int dstheight, int dstformat);
 
 #endif // COMMON_H

src/modules/avformat/consumer_avformat.c

@@ -1925,8 +1925,9 @@ static void *consumer_thread( void *arg )
 						mlt_image_format_planes( img_fmt, width, height, image, video_avframe.data, video_avframe.linesize );
 
 						// Do the colour space conversion
-						int flags = mlt_default_sws_flags;
-						struct SwsContext *context = sws_getContext( width, height, pick_pix_fmt( img_fmt ),
+						int srcfmt = pick_pix_fmt( img_fmt );
+						int flags = get_sws_flags( width, height, srcfmt, width, height, pix_fmt);
+						struct SwsContext *context = sws_getContext( width, height, srcfmt,
 							width, height, pix_fmt, flags, NULL, NULL, NULL);
 						int src_colorspace = mlt_properties_get_int( frame_properties, "colorspace" );
 						int src_full_range = mlt_properties_get_int( frame_properties, "full_luma" );

src/modules/avformat/filter_avcolour_space.c

@@ -84,7 +84,7 @@ static int av_convert_image( uint8_t *out, uint8_t *in, int out_fmt, int in_fmt,
 	int in_stride[4];
 	uint8_t *out_data[4];
 	int out_stride[4];
-	int flags = mlt_default_sws_flags;
+	int flags = get_sws_flags( width, height, in_fmt, width, height, out_fmt);
 	int error = -1;
 
 	if ( in_fmt == AV_PIX_FMT_YUV422P16LE )

src/modules/avformat/producer_avformat.c

@@ -1331,7 +1331,6 @@ static int sliced_h_pix_fmt_conv_proc( int id, int idx, int jobs, void* cookie )
 static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffer, int pix_fmt,
 	mlt_image_format *format, int width, int height, uint8_t **alpha )
 {
-	int flags = mlt_default_sws_flags;
 	mlt_profile profile = mlt_service_profile( MLT_PRODUCER_SERVICE( self->parent ) );
 	int result = self->yuv_colorspace;
 
@@ -1368,11 +1367,14 @@ static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffe
 		// Thankfully, there is not much other use of yuv420p except consumer
 		// avformat with no filters and explicitly requested.
 #if defined(FFUDIV)
+		int flags = get_sws_flags(width, height, src_pix_fmt, width, height, AV_PIX_FMT_YUV420P);
 		struct SwsContext *context = sws_getContext(width, height, src_pix_fmt,
 			width, height, AV_PIX_FMT_YUV420P, flags, NULL, NULL, NULL);
 #else
+		int dst_pix_fmt = self->full_luma ? AV_PIX_FMT_YUVJ420P : AV_PIX_FMT_YUV420P;
+		int flags = get_sws_flags(width, height, pix_fmt, width, height, dxt_pix_fmt);
 		struct SwsContext *context = sws_getContext( width, height, pix_fmt,
-					width, height, self->full_luma ? AV_PIX_FMT_YUVJ420P : AV_PIX_FMT_YUV420P,
+					width, height, dxt_pix_fmt,
 					flags, NULL, NULL, NULL);
 #endif
 
@@ -1392,6 +1394,7 @@ static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffe
 	}
 	else if ( *format == mlt_image_rgb24 )
 	{
+		int flags = get_sws_flags(width, height, src_pix_fmt, width, height, AV_PIX_FMT_RGB24);
 		struct SwsContext *context = sws_getContext( width, height, src_pix_fmt,
 			width, height, AV_PIX_FMT_RGB24, flags, NULL, NULL, NULL);
 		uint8_t *out_data[4];
@@ -1405,6 +1408,7 @@ static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffe
 	}
 	else if ( *format == mlt_image_rgb24a || *format == mlt_image_opengl )
 	{
+		int flags = get_sws_flags(width, height, src_pix_fmt, width, height, AV_PIX_FMT_RGBA);
 		struct SwsContext *context = sws_getContext( width, height, src_pix_fmt,
 			width, height, AV_PIX_FMT_RGBA, flags, NULL, NULL, NULL);
 		uint8_t *out_data[4];
@@ -1422,7 +1426,6 @@ static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffe
 		int i, c;
 		struct sliced_pix_fmt_conv_t ctx =
 		{
-			.flags = flags,
 			.width = width,
 			.height = height,
 			.frame = frame,
@@ -1435,6 +1438,7 @@ static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffe
 		ctx.src_format = (self->full_luma && src_pix_fmt == AV_PIX_FMT_YUV422P) ? AV_PIX_FMT_YUVJ422P : src_pix_fmt;
 		ctx.src_desc = av_pix_fmt_desc_get( ctx.src_format );
 		ctx.dst_desc = av_pix_fmt_desc_get( ctx.dst_format );
+		ctx.flags = get_sws_flags(width, height, ctx.src_format, width, height, ctx.dst_format);
 
 		av_image_fill_arrays(ctx.out_data, ctx.out_stride, buffer, ctx.dst_format, width, height, IMAGE_ALIGN);
 
@@ -1465,9 +1469,11 @@ static int convert_image( producer_avformat self, AVFrame *frame, uint8_t *buffe
 #else
 	{
 #if defined(FFUDIV)
+		int flags = get_sws_flags(width, height, src_pix_fmt, width, height, AV_PIX_FMT_YUYV422);
 		struct SwsContext *context = sws_getContext( width, height, src_pix_fmt,
 			width, height, AV_PIX_FMT_YUYV422, flags, NULL, NULL, NULL);
 #else
+		int flags = get_sws_flags(width, height, pix_fmt, width, height, AV_PIX_FMT_YUYV422);
 		struct SwsContext *context = sws_getContext( width, height, pix_fmt,
 			width, height, AV_PIX_FMT_YUYV422, flags, NULL, NULL, NULL);
 #endif