Sophie: blender-manual-2.49a-1ark i586

blender-manual-2.49a-1ark.i586.rpm

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>Preparing your work for video</TITLE
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>Blender Documentation Volume I - User Guide: Last modified April 29 2004 S68</TH
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><H1
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><A
NAME="rendering_preparing_for_video"
></A
>Preparing your work for video</H1
><P
>&#13;		Once you have mastered the trick of animation you will surely
		start to produce wonderful animations, encoded with your
		favourite codecs, and possibly you'll share them on the internet with the rest of
		the community.
		</P
><P
>&#13;		But, sooner or later, you will be struck by the desire of building an animation for
		Television, or maybe burning you own DVDs.
		</P
><P
>&#13;		To spare you some disappointment, here are some tips specifically targeted at Video preparation.
		The first and principal one is to remember the double dashed white lines in the camera view!
		</P
><P
>&#13;		If you render for PC then the whole rendered image, which lies within the
		<I
CLASS="emphasis"
>outer</I
> dashed rectangle will be shown. For Television
		some lines and some part of the lines will be lost due to the mechanics of 
		the electron beam scanning in your TV's cathode ray tube. You are guaranteed
		that what is within the <I
CLASS="emphasis"
>inner</I
> dashed rectangle
		in camera view will be visible on the screen. Everything within the two
		rectangles may or may not be visible, depending on the given TV set
		you watch the video on.
		</P
><P
>&#13;		Furthermore the rendering size is strictly dictated by
		the TV standard. Blender has three pre-set settings for your
		convenience:
		</P
><P
></P
><UL
><LI
><P
><TT
CLASS="literal"
>PAL</TT
> 720x576 pixels at 54:51 aspect ratio.</P
></LI
><LI
><P
><TT
CLASS="literal"
>NTSC</TT
> 720x480 pixels at 10:11 aspect ratio.</P
></LI
><LI
><P
><TT
CLASS="literal"
>PAL 16:9</TT
> 720x576 at 64:45 aspect ratio, for 16:9 widescreen TV renderings.</P
></LI
></UL
><P
>&#13;		Please note the "Aspect Ratio" stuff. TV screens do <I
CLASS="emphasis"
>not</I
> have
		the square pixels which Computer monitors have, their pixels are somewhat
		rectangular, so it is necessary to generate <I
CLASS="emphasis"
>pre-distorted</I
>
		images which will look bad on a computer but which will display
		nicely on a TV set.
		</P
><DIV
CLASS="section"
><H2
CLASS="section"
><A
NAME="rendering_preparing_for_video_saturation"
></A
>Colour Saturation</H2
><P
>&#13;		Most video tapes and video signals are not based on the RGB model
		but on the YUV, or YCrCb, model in Europe and YIQ in the USA, this latter
		being quite similar to the former. Hence some knowledge of this
		is necessary too.
		</P
><P
>&#13;		YUV model sends info as 'Luminance', or intensity (Y) and two 'Crominance' signals, red
		and blue. Actually a Black and White TV set shows only luminance, while colour
		TV sets reconstructs colour from Crominances. It is:
		</P
><P
>&#13;		Y = 0.299R + 0.587G + 0.114B
		</P
><P
>&#13;		U = Cr = R-Y
		</P
><P
>&#13;		V = Cb = B-Y
		</P
><P
>&#13;		Whereas a standard 24 bit RGB picture has 8 bit for each channel, to
		keep bandwidth down, and considering that the Human eye is more
		sensitive to luminance than to crominance
		the former is sent with more bits than the two latter.
		</P
><P
>&#13;		This results in a smaller dynamic of colours, in Video, than that
		you are used to on Monitors. You hence have to keep in mind not all 
		colours can be correctly displayed. Rule of thumb is to keep the colours as
		'greyish' or 'unsaturated' as possible, this can be roughly
		converted in keeping the dynamics of your colours within 0.8.
		</P
><P
>&#13;		In other words the difference between the highest RGB value and the lowest
		RGB value should not exceed 0.8 ([0-1] range) or 200 ([0-255] range).
		</P
><P
>&#13;		This is not strict, something more than 0.8 is acceptable, but a 
		RGB=(1.0,0,0) material will be very ugly.
		</P
><DIV
CLASS="section"
><H3
CLASS="section"
><A
NAME="rendering_preparing_for_video_fields"
></A
>Rendering to fields</H3
><P
>&#13;		The TV standard prescribes that there should be 25 frames per second (PAL) or 30 frames per second
		(NTSC). Since the phosphorous of the screen does not maintain luminosity for very long, this
		could produce a noticeable flickering. To minimize this TVs do not represent frames as a Computer does
		but rather represents half-frames, or <I
CLASS="emphasis"
>fields</I
>
		at a double refresh rate, hence 50 half frames per second on PAL
		and 60 half frames per second on NTSC. This was originally bound to the frequency of power 
		lines in Europe (50Hz) and the US (60Hz).
		</P
><P
>&#13;		In particular fields are "interlaced" in the sense that one field presents all 
		the even lines of the complete frame and the subsequent field the odd ones.
		</P
><P
>&#13;		Since there is a non-negligible time difference between each field (1/50 or 1/60 of a second)
		merely rendering a frame the usual way and
		splitting it into two half frames does not work. A noticeable jitter of
		the edges of moving objects would be present.
		</P
><DIV
CLASS="figure"
><A
NAME="BSG.REN.F.S68.1001"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartR/rendering/gfx/Fields01.png"></P
></DIV
><P
><B
>Figure 38. Field Rendering setup.</B
></P
></DIV
><P
>&#13;		To optimally handle this issue Blender allows for field rendering. When the 
		<TT
CLASS="literal"
>Fields</TT
> button in the <TT
CLASS="literal"
>Render</TT
>
		Panel is pressed (<A
HREF="x8067.html#BSG.REN.F.S68.1001"
>Figure 38</A
>)
		Blender prepares each frame in two passes. On the first it renders only
		the even lines, then it <I
CLASS="emphasis"
>advances in time by half time step</I
>
		and renders all the odd lines.
		</P
><DIV
CLASS="figure"
><A
NAME="BSG.REN.F.S68.1002"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartR/rendering/gfx/Fields02.png"></P
></DIV
><P
><B
>Figure 39. Field Rendering result.</B
></P
></DIV
><P
>&#13;		This produces odd results on a PC screen (<A
HREF="x8067.html#BSG.REN.F.S68.1002"
>Figure 39</A
>)
		but will show correctly on a TV set.
		</P
><P
>&#13;		One of the two buttons next to the <TT
CLASS="literal"
>Fields</TT
> button forces the
		rendering of Odd fields first (<TT
CLASS="literal"
>Odd</TT
>) and the other disables
		the half-frame time step between fields (<TT
CLASS="literal"
>x</TT
>).
		</P
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>Setting up the correct field order</B
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><P
>&#13;		Blender's default setting is to produce Even fields Before Odd fields, this
		complies with European PAL standards. Odd fields are scanned first on NTSC.
		</P
><P
>&#13;		Of course, if you make the wrong selection things are even worse than if no Field
		rendering at all was used.
		</P
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