All posts by Xuran Ni

I tracked the plate in two parts before but I realize that I only need one camera, in this case I re-track the plate with suitable lens undistortion and other given parameters, and it works very well, better than before.

3D Tracking

I write out the camera and some planes as reference and import them in maya. I also improt the undistorted plate image sequence as background, as well as HDRI.

We do not use HDRI to cast shadows because it will cause shadows on undesirable places. I just choose to use area lights to mimic the effect.

camera sample should be larger than 3 if using casting shadows.

More info: https://docs.arnoldrenderer.com/display/A5AFMUG/Shadow+Matte

Multipass rendering

Mid-drag the assets in suitable collections under the layers that we created, we can create Override to exclude the unwanted assets in the scene. In this case, we just separate shadow and no shadow scenes.

To save time, I choose to render different layers separately, as GPU rendering does not support shadow matte alpha channel, I deicide to render geo_no_shadow layer by GPU and shadows layer by CPU.

Because I forgot to render with ID pass, so I have to roto the part that I want to correct separately and merge them afterwards. It is important to care about the alpha channel in each node, and I just turn the alpha into black colour in roto node. And we need to grade with alpha mask, or premult in advance, otherwise it may affect the original plate.

Final Compositing

Protected: Project Summary and Business Plan

23rd March 2021Collaborative ProjectXuran Ni

Week 8|Green Screen Extraction

11th March 2021NUKEⅡXuran Ni

IBK

IBK (Image-Based Keyer) is a non-native node to nuke, it was developed in a studio.

Increasing to a large size in IBKColour node to clean the plate may cause atrfacts, instead, we adjust darks to correct the edges and use stacked IBKColour nodes to shrink the objects. Then connect to IBKGizmo node to show the objects.

We can create two green constants, one from the bright region, one from the dark region, to even the green screen.

Keylight

Import camera for CG compositing

10th March 20213D CGⅡXuran Ni

First we need to import image sequence, we need to make sure the image sequence name is ended with number, avoid A01_0001.tiff this type of file name, otherwise maya cannot import image sequence automatically.

I just import the camera created from nuke and view from the imported camera. I made a sphere and put it on the position of the axis that I created in nuke.

The image sequences can be hidden:

Import the correct HDRI in Alnold SkydomeLight, set the camera visibility to zero, the environment effect will be kept but HDRI will be removed.

Week 7|3D Projections_Crypt A01

9th March 2021NUKEⅡXuran Ni

We need to cleanup the plate for CG compositing.

Cleanup

Week 7|3D Projections

8th March 2021NUKEⅡXuran Ni

This week we use 3D projection to clean the plate(remove unwanted assets).

I just use the 3D tracking piece from week 4 to do the projections. And I choose to remove the toys on the ground.

3D tracking from week 4

3D Projections Cleanup

For the object between different planes, we can create patches for different part in planes separately. We just rotopaint in good frame as normal and create the projection regions, then hold the chosen frame.

In 3D projections, we need the same camera as before, but this time we call it the projector(Blue one). We need to hold the projector in the chosen frame as well.

We can build the cards directly using the modelbuilder node, position the required cards in correct region for the patch that we created. This time I just adjust the cards in 3D tracking and import them into 3D projections. Remember the cards should be renderd in texture.

Tips: We can use cornerPin nodes to deal with the sides between the planes. The second cornerPin is the same parameters as the first one, but inverted.