Preparing your work for video

Once you mastered the animations trick you will surely start to produce wonderfull animations, Encoded with your favourite codecs and possibly share it on the internet with all the community.

But, sooner or later, you will be struck by the desire of building an animation for Television, maybe burning you own DVDs.

To spare you some disappointments here are some tips specifically targeted at Video preparation. The first and principal is to remember the double dashed white line in camera view!

If you render for PC then the whole rendered image, which lies within the outer 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 cathodic ray tube. You are guaranteed that what is within the inner dashed rectangle in camera view will be visible on the screen. Everything within the two rectangles may and may not be visible, depending on the given TV set you will see the video on.

Furthermore the rendering size is strictly dictated by the TV standard. Blender has three pre-set settings for your convenience:

Please note the "Aspect Ratio" stuff. TV does not have square pixels as Computer monitors have, their pixel is somewhat rectangular, so it is necessary to generate pre-distorted images which will look crap on the computer but which will be shown nicely on TV set.

Blender has memorized as presets the correct aspect ratios for regular PAL, 16:9 PAL and NTSC.

Color Saturation

Since most video tapes and video signals are not based at RGB model but on YUV, or YCrCb, model in Europe and YIQ in US, this latter being quite similar to the former.

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:

Y = 0.299R + 0.587G + 0.114B

U = Cr = R-Y

V = Cb = B-Y

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 that to crominance the former is sent with more bits than the two latter.

This results in a smaller dynamics of colours, in Video, than that you are used to on Monitors. You hence have to keep in mind not all colors can be correctly displayed. Rule of thumb is to keep the colors as 'greyish' or 'unsaturated' as possible, this can be roughtly converted in keeping the dynamics of your colours within 0.8.

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).

This is not strict, something more than 0.8 is acceptable, but a RGB=(1.0,0,0) material will be very ugly.

Rendering to fields

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 do not maintain luminosity too long this could produce a noticeable flickering. To minimize this TV do not represent frames as Computer does but rather represent half-frames, or fields 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 US (60Hz).

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.

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 split it into two half frames does not work. A noticeable jitter of the edges of moving objects would be present.

Figure 39. Field Rendering setup.

To optimally handle this issue Blender allows for field rendering. When the Fields button is pressed (Figure 39). Blender prepares each frame in two passes, on the first it renders only the even lines, the it advances in time by half time step and renders all the odd lines.

Figure 40. Field Rendering result.

This produces odd results on a PC screen (Figure 40) but will show correctly on a TV set.

The two buttons next to the Fields button forces the rendering of Odd fields first (Odd) and disable the half-frame time step between fields (x).

TipSetting up the correct field order
 

Blender default setting is to produce Even field Before Odd field, this comply to European PAL standards. Odd field is to be scanned first on NTSC.

Of course if you make the wrong selection things go even worse that if no Field rendering at all was used.