My VFX Blog

We have been exploring the process of green screen removal, which involves extracting the green background from a video and replacing it with other visuals.

One of the techniques we have covered is the use of the hue correct node, which enables us to remove the green color from our footage by creating a node graph. By selecting the green color in the graph and dragging it down, we were able to effectively remove the green screen from our footage and prepare it for the insertion of other visuals. While this technique may seem relatively straightforward, it can be a powerful tool for creating compelling visual effects.

We also explored the key luminance node, which can be used to selectively affect certain areas of an image or video. This technique involves creating an alpha image and selecting the specific areas that we want to modify.

During our lesson, we experimented with this technique by selecting only the sky in our footage and adjusting the levels at which it was selected. This enabled us to fine-tune the visual effect to create a more natural and realistic result. Overall, the key luminance node is a valuable tool that can be used to create a wide range of compelling visual effects.

We explored how to adjust the lighting in specific areas of an image or footage. During our lesson, we used rotoscoping to isolate the particular area we wanted to modify, and then applied various nodes, including the shuffle, grade and keyer node, to enhance the lighting and make it appear brighter, we used this example of a snowy landscape to make the bottom half more light.

We then looked at creating rays of light coming out from behind objects such as trees. This enhances the lighting apparent behind an object. This was done by using a node called volume rays, along with the selection of just the tree using rotoscoping.

We also learned a basic technique for creating a blurred effect in a specific area of an image using rotoscoping. This technique involves using an image to create a rotoscope of a circular area, and then applying a blur node to that area. Finally, we merged the two to create the look of a blurred circle in the specific area of the image.

Work from home

For the garage project I felt like I needed to add another big asset to the scene.

I decided to add ladders to fit the theme of the project. This also fit in well with my other assets such as the tyre and the mechanical posters. I downloaded a 3D model of four ladders together. I then added the texturing in Maya adjusted the placement of the ladders.

I then rendered these out and added this file to my Nuke garage project script.

I then followed the same method I had used on my other assets and tracked these ladders through the camera tracker, and then synced this up to the scene. Again, I used the axis on the wall I wanted them to stay against and then created a card which I then linked to the original image of the 3D models. These then successfully tracked with the camera and moved with the footage.

I then had to do the homework we were given which was linked to the green screen methods we had been using. I first tried using the hue correction node and the keyer node to adjust the levels of permittance. However, this was picking up on too much green in the image.

I decided to use another method we were shown for this task.

For this I used the Keylight node in which you can select a colour using the eyedropper tool and adjust how much of the levels you want to be removed on the footage of this specific colour. I selected the green on the green screen and adjusted the numbers until it was at a level of green removal that looked professional.

This week we looked at how to create a realistic CG composition, and apply this knowledge to our garage project.

Simply merging the asset to the background isn’t enough for a realistic CG comp. We looked at colour correction, as a way for the assest to blend into the scene more seamlessly. Splitting the channels to do this enables us to merge each channel and see the progess of the asset in the desired position. Nodes such as the shuffle and grade nodes contribute to colour correction of an asset.

We then looked at inputting smoke into the second room. This contained the rotoscoping we did and also working with the camera tracking we had learnt in previous weeks.

Work from home

To progress on our garage project, we now had to apply our knowledge of realistic CG composition and add some more assets to our scene.

I decided I wanted to add a tyre to the scene, leaning against the wall, as this would fit the theme of the scene. I downloaded a 3D model of a tyre, loaded it on Maya and started editing it slightly.

I made it slightly thinner and added spotlights coming from the direction the light is coming from in the scene. Then I made sure it looked okay on the render screen and rendered it out to an exr file to input on to Nuke.

I then placed this on the scene in Nuke, in my desired area I wanted it to be in.

I then had to track it to move with the camera. This was the most difficult part of this task this week as all prior ways I have done this didn’t seem to be working. After adding the tyre to the axis point I created a card on, and reading it through that, it tracked, however the positioning wasn’t right. After playing around with the card, the rotation and size I managed to get it to look right. However, the the tyre needs more colour correction and a shadow to blend. I added a grade node and adjusted some colour gradients, as well as changing the input to RGB instead of linearr, but it needs more focus on colour correction and shadowing.

I then used the same approach and template to add two posters on the walls. I decided to add mechanical posters to suit the theme, however these need shadowing as well. I have slightly changed the gain on the grade node of the white poster, as it is slightly out of the light, however the black poster seems to have the appropriate colours and light gain for where it is placed.

This week we looked at seperating and linking ‘passes’ within an image on Nuke. This means all the seperate nodes such as grading, diffusing, specular and refraction nodes. We can see what goes into making up the image. If we pull up the lens contact sheet node we can see all of the changes the image has gone through and how these come together.

By changing the colour on the grade node to red, we can see what part the grading affects the image overall.

We then looked at a more complex and varied version of a lens contact sheet. This time, with an image of a car. We can see different effects Nuke can produce such as a UV screen and a wireframe image.

We then took the 3D image of the car, and looked more into UVs on the 3D viewport. Through using the nodes shown below we were able to see the 3D model of the car in a UV lens, and through an inverted black and white lens.

Work from home

After some guidance from our teacher, I was finally able to complete the cloning and clean up on our garage project. I realised after advice that I was not using the 3D card node right. I needed to create cards from the tracking points, and attach these to the scene. I was then able to roto around these and sucessfully make them disapear and blend in with the background.

Then, again with guidance, I also resolved my roto of the wall problem. I used a correct template to follow the correct nodes, and again I was using the card incorrectly. I also needed to add back the lens distortion, perfect the tracking by adjusting the points at some frames, and then this roto tracked with the camera.