When tracking a plane in a perspective movement, I tried to make a loop on the monitor.

It is noticeable that the output from cornerpin2D node contains an alpha channel. If we want to add on any elements, we need to premult it before sending it to the next cornerpin2D, otherwise alpha channel will double in the matching region.

This time, I tried to clean-up the plate firstly, and place a transparent logo image on the headphone. It is quite tricky to remove the original logo, because the existing reflection light is changing.

I tried to re-roto my first rotoscoping, and use the grade node to match the colour with the background plate.

I tried to place a logo on the headphone this time:

Parameters variation in grade node:

Lift performs in an opposite way to blackpoint, wheras gain performs in an opposite way to whitepoint.

Multiply performs in the same way as gain.

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Source：

Cleanup is an important but also time-expensive process in VFX pipeline. We need to remove the unwanted elements from the shot and make sure the affected region in the original plate as less as possible. Roto and tracking techniques are used to help cleaning up.

Rotopaint node is just an older version compared with roto node, the former contains more actions than the latter, such as clone. Clone is mostly used in cleanup.

We may need to denoise the plate firstly to help tracker work in a better performance. On the other hand, since the noise is generated randomly, we need to create a cleaned part based on denoised background, otherwise the cleaned part will contain fixed noise. Finally, we can use regrain to generate a similar and dynamic noise subject to the original plate.

When doing cleanup, there are loads of factors to consider about, such as the change on the environment due to the removed elements. In this shot, the shadow behind the cup should be removed along with the cup itself.

2D Tracking （For Parallax Motion）

Shots without spatial or perspective movement can use 2D tracking, such as parallax movement.

Quality Control using Laplacian node:

The region outside of the replacement feature is all black, which means it is good.

Planar Tracker (For Perspective Motion)

Shots without spatial movement can use planar tracker, such as perspective movement or parallax movement.

We have two ways to create a planar tracker node, by searching for planar tracker or converting a roto node to a planar tracker, as it is a kind of roto node literally.

We have some choices in tracking setting when exporting a roto node, tracker is an option.

With relative cornerpin2D, the asset image stays the same, following the tracking information to move.

With absolute cornerpin2D, the asset image will be altered to fit the selected tracking plane when following the tracking path.

In the case that we need to adjust the image to proper shape and position, we need another cornerpin node to do a transfer.

More info:

https://learn.foundry.com/nuke/content/comp_environment/planartracker/tracking_plane.html

Before tracking the image sequences, we always denoise the original plates, sometimes people use median node as well. Grade node is another helpful tool to increase the contrast. However, denoise and median nodes usually cause crash, so remember to export the sequences and reload it again as the new denoised image sequences to carry on the project in Nuke.

Here is an example that I did for 2D tracking:

I used the denoised image sequences to complete the tracking process, and then apply it to the original image sequences.

There are three term to consider with colour correction: Hightlights, Midtones, Shadows.

Grade

Grade node is one of the most powerful nodes in Nuke, it can be used to white-balance the image sequences by sampling the whitepoint and blackpoint; change the darkest(shadows) and lightest area(highlights) by adjusting lift and gain. Gamma can be used to grade midtones. We can also choke the image by adjusting gamma through alpha channel.

We always grade the unpremulted images, so we need to unpremult the image firstly if necessary, then premult it after grading. We need the premulted images for assets added on the background before compositing.

More info see:

https://learn.foundry.com/nuke/content/reference_guide/color_nodes/grade.html?Highlight=grade

https://learn.foundry.com/nuke/content/reference_guide/merge_nodes/premult.html?Highlight=premult

ColorCorrect

ColorCorrect is a more precise node compared to grade node, it can be used to modify the shadows, midtones and highlights. Here offset is used to grade shadows, similar as lift in grade node.

We can modify the region curves to change the particular regions that we want to control.

See more: https://learn.foundry.com/nuke/content/reference_guide/color_nodes/colorcorrect.html?Highlight=color%20correct

Colour matching plates

In order to create compositing more naturally, it is necessary to control the colour settings for the elements. I chose 2 still images to try this task as follows:

Original images:

White-balancing is the first step of the colour matching, by choosing both the darkest and brightest points when viewing in Luminance mode (shortkey y), as well as adjusting gamma parameter until I find no difference before and after grading the images.

Then I used Grade node to match the colour of the two images, by adjusting lift and gain parameters to match the shadow and highlight respectively.

Review:

The two original images are not matched so properly due to other factors such as lighting and angle of shot, which should be taken into consideration before compositing.