2.2 Fixing a Film Tear
In our previous extended study material for the Level 2 PFClean training (2.1 Degrain and Regrain), we went over a couple of different methods for building a grain profile to use in your project. In this extended study we will be tackling the first of a number of film defects that we noticed in the Chanti footage.
If you haven’t completed the previous tutorial 2.1 Degrain and Regrain I would suggest going back and starting from there as we will be using some of the material and profiles we generated.
NOTE: To follow along in this tutorial, you will need access to the clips provided for the class. If you don’t have them to hand, below you will find the link to download the footage again.
01. Adjusting Pixel Aspect
Let’s start where we previously left off setting up a grain profile on our shots. Having deleted the De-Grain and Re-Grain effects from our shots, let’s make sure we are in the Workbench and looking at CHANTI_SHOT_003.
Press the play button to preview the shot, on frame 8 we can see the film tear horizontally across the shot. During playback you may have noticed that the footage actually looks squeezed. This is because the original footage was shot in the cinemascope format.
Let’s now correct the ratio so it looks normal in the cinema before we begin work. Just below the cinema the is a button for adjusting the pixel ratio. At the moment it is currently set to Auto so we are going to click on the dropdown and select the ratio Cinemascope half from the list. In the cinema we can now see that the ratio has been corrected.
NOTE: Changing the pixel aspect ratio will affect viewing in the cinema.This will not change the ratio of an export.
02. Adding Fix Tear Effect
Now that we are looking at the image correctly let’s add in a new effect into the stack called Fix Tear, this can be found under the Repair Operations. When we step backwards and forwards through the clip using the left and right arrow keys, around where the tear is you will notice that part of the image is actually distorted slightly and out of alignment. The Fix Tear tool is a quick and powerful way of removing this distortion and fixing the tear itself. In effect we are splicing the displaced film back into position.
Before we start using the Fix Tear let’s go through some of the preferences available to you in the edit panel at the bottom of the GUI.
03. Fix Tear Settings
The Motion drop down menu is used to specify the type of motion that is needed to re-align the torn part of the frame. In our case we are going to use Trans + Rot as the displaced part of the film moves mostly on the y axis but with slight rotation and slight x axis movement.
Below this we have the Deflicker, which allows control over whether brightness variations will be accounted for when fixing. In our case we have some very slight variations in luminance so we will be switching this button on.
The Grain/Noise Preset menu allows a preset to be used to render grain or noise over the top of the repaired region. This can often improve the quality of the fix in situations where the repaired tear region is too smooth. This will be the first time where we get to use one of our grain profiles we generated in tutorial 2.1 Degrain and Regrain. Let’s select either chanti_m1 or chanti_m2 from the list.
The Frame Lookahead parameter is used to specify the direction and frame that the tear will be re-aligned to. In our case we can leave this at its default of -1 which means it will use the previous not torn frame to re-align to.
The next sliders are Border Size and Matte Threshold. The Border Size controls the size of the region around the tear that will be used to estimate motion when removing the tear artifacts, increasing this increases the amount of image used, in our case we are going to leave it at it’s default.
The Matte Threshold specifies the threshold used to decide if a pixel is corrupted by the tear or not. The default is 3% but we are going to reduce this to around 2%. This means if the pixel differs from the original by at least 2% it will be included in the fix.
The Sensitivity parameter controls the error threshold for motion analysis. The default is 25%, meaning that pixels which differ by more than this value are considered to be incorrectly tracked, and will not contribute to the motion estimate.
04. Drawing Before and After Tear
From there we are going to draw polyline around the areas before the tear, being careful not to include any of the tear itself in the area. Once we complete the polyline you will notice it automatically selects the button. So let’s go ahead and draw the polyline after the tear, again being careful not to include any of the tear itself in the area. If you make a mistake don’t worry clicking the Clear Boundary will reset the polylines.
05. Fixing the Tear
Once a tear has been fixed, the Frames List contains all frames that have been corrected. If your clip contains multiple tear fixes, multiple frames and fixes will be displayed here and can be deleted per fix or per frame.
06. Before or After?
One question is, what do you consider before the tear and what do you consider after the tear? Normally the part of the frame that moves out of alignment is what we consider after the tear or the part that we want to bring back into alignment. If both sides are out of alignment by a long way it is at this point we might want to consider using the Fix Frame tool in the Repair Operations instead.
Don’t worry if the fix tear hasn’t removed all the sparkle, we will be using a couple of other tools to fix that and repair the bottom and side of the frame later on. Let’s now move on to the next tutorial and repair another common issue, film warping.