For a basic understanding of CGI or visual effects click here.
The Christmas Eve Snowfall (2005)

The Christmas Eve Snowfall was the most effects heavy film ever produced by Hanover Pictures. In total 34 visual effects shots were needed to complete the film produced during the 10 months post-production schedule. The following shots give you an idea of how "compositing" works taken from the film. The sequence near the end of the movie invloves a young girl looking out her window to see the newly met couple sat on a park bench. Due to the cast and weather conditions not being able to be on the location at the same time, a "composite" shot was required.
Click on an image to enlarge it.
The shot breaks down as follows.

1. The empty background plate, notice the blue light and uneven snow

2. More snow is painted on

3. The shot is warmed
and a sun rise is added

4. Actors are shot on a snowy bench, months later

5. The actors are "rotoscoped"
or cut out of the unwanted
background.

6. The actors are placed in the shot and computer graphic snow is added.

Another example of "compositing" is taken from the beginning of the film, as we're introduced to the character of Macmillan Croy as he stands on a clifftop. In the real world, the moon wouldn't light the calm ocean so ideally, let alone be in the correct position or be able to be photographed without having exposure problems. So to achieve this look, it had to be done digitally.

1.Actor Ben Pavord stands against
the background on partial snow

2.More snow is painted in

3.The moon and CG stars are added

4.Ben is rotoscoped out and the sea is put in the background

To see this clip click on the picture
"Meet the lone Macmillan Croy..."

Running time: 47 seconds

"The Christmas Eve Snowfall" required multiple computer generated shots. A digital snowflake was created to feature in 12 of the shots, along with digital backgrounds, sea, sky and snow. The poem contains one short line that reads how a snowflake comes down from the heavens. For this particular shot a completely computer generated shot was produced with no live action elements at all. With any computer generated sequences, render times are very high. "Rendering" is when the computer puts together all the CG elements with lighting, textures and motion ready to be placed in the final film. For "The Christmas Eve Snowfall's" complete CG shot lasting 6 seconds, rendering time was 17 hours.
Katie's Mission (2004)
Katie's Mission required the use of Digital Effects. Scenes that involved the baby had to be digitally put in as baby Katie (Adele Jade Elliman) was never on set. Shots of the actors were taken on location holding a doll wrapped in the baby blanket and were composited with shots taken of the baby at her home. Baby Adele has to rotoscoped (cut out) out of the original shots frame by frame and placed over the location background plates. A digital light is then place in the scene to light the baby the same as the actor who was actually filmed 6 months after. In total there are 7 visual effects shots in "Katie's Mission".
Other shots included a Computer Generated Airplane when a German fighter plane flies over head. The plane was animated and composited with the empty background plate taken on location. Trees on location were digitally cut out from the scene and placed back in over the top of the animated plane to give the impression that the plane was flying behind the trees.
For the end battle scene, digital smoke effects were composited into the action shots to show bullet hits richoceting off walls and bunkers. Again, the colour of the smoke had to match the light and other smoke shot on the day to make the effects seamless.