2.4 Fixing Faded and Colour Shifted Film
In our previous extended study material for the Level 2 PFClean training (2.3 Fixing Film Warp) we were looking at stretch and squashing artefacts caused by film warp in CHANTI_SHOT_001 and how to fix it using the De-Warp tool in the Workbench. In this extended study tutorial we will be looking at the second Chanti shot and tackling another common issue, colour shifting and fade.
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. Adding the Colour Balance Effect
Let’s start where we left off on the previous tutorial which was our De-Warp in CHANTI_SHOT_001. From here go to CHANTI_SHOT_003 either by clicking on the clip in the Worklist or the forward arrow at the top left of the GUI. In both of these shots you will notice a distinct green hue which has been caused by a colour shift in the film stock. A frequent problem especially in the unstable film stocks of the 60s through to the 80s where pink and magenta hues are commonly seen.
So how do we fix this problem in PFClean? We are going to use the Colour Balance effect found in the Colour Operations in the Workbench. Making sure we are on CHANTI_SHOT_003 let’s go ahead and add a Colour balance effect to the effects stack under the Fix Tear.
02. The Colour Balance Effect
The Colour Balance effect restores colour shifts by mapping source colours to target colours. The source colours are usually sampled from the image, but can also be specified manually, and then transformed into more neutral target colours.
When using the Colour Balance effect, you have a wide range of options to refine both source and target colours to achieve the best possible results.
03. Adjusting Source Colours
By default, only chrominance values are sampled. You can change this individually for the black, balance and white points with the drop down menus. Selecting Luminance only samples luminance information and can be used to restore a more natural contrast range without affecting colour, while RGB samples both, chrominance and luminance. Let’s go ahead and select RGB for Black Point, Balance Point and White Point. We also need to re-sample the image for these changes to have an effect so let’s click Balance Frame to do this.
The source colours define the colour present in the unrestored image for example for a green tint we will push towards green in the colour wheel to correct for this. These will then be mapped to target colours. The source colours can be adjusted or sampled manually if required. Let’s click and drag the indicator in the Balance Point colour wheel to see the effect.
04. Manual Sampling
Manual colour balance can be performed by clicking one of the Black Point, Balance Point or White Point buttons and clicking (or clicking and dragging) with the left mouse button in the Cinema window will sample a colour from the image. Let’s give that a try now by clicking on the Black Point button and selecting from the soundtrack area on the left, then the White Point and select from maybe the background on the right hand side. Now let’s press the Balance Point and select the grey pillar behind the characters.
The edit boxes, colour wheels and channel transfer will update accordingly and the colour balance will be applied immediately. If the result is not acceptable you can pick another colour easily from another part of the image. If you are removing a colour tint, try to pick a Balance Point colour from an area of the image you know should be grey (or another known colour); in our case the grey pillars behind the characters.
05. Animating a Colour Shift
In some cases, the amount of colour shift varies throughout clips. To successfully tackle varying colour shift, you can animate the Colour Balance parameters. Although our clip is consistent in its colour shift throughout, let’s have a go at animating the clip as a demonstration.
The first thing we are going to do is go to the last frame of the clip, frame 47. Now drag the Balance Point colour wheel over towards the red slight so that there is a visible change in the image. Now go to the middle of the clip around frame 23 and drag the Balance Point colour wheel towards the blue. Again the same for the first frame in the sequence but this time towards green. When we play through the clip we will see the Balance Point colour wheel animate through the different colours that we set.
You can also view and edit keyframes in the Workbench’s F-Curve editor. Click this button to open the editor. The F-Curve editor is not part of this extended study material, but you can find out more about editing f-curves in PFClean by clicking the button. Clicking Balance Clip will automatically sample the source black point, balance point and white point for all frames individually.
If go back to the first frame and click the Balance Frame button and then click the Constant button and play through we will see that that balanced value will remain constant throughout the clip.
NOTE: Clicking either, Balance Frame or Balance Clip will overwrite the current parameters, unless they have been locked in the Offsets tab, which is described below.
06. Target Colours
The Colour Balance effect maps the source colours to the default neutral colours in the Target Colours tab. You can adjust or sample Target Colours the same way as the source colours. When the Target Colours tab is visible, selecting Black Point, Balance Point or White Point will sample a target colour rather than a source colour. You can also adjust the target colour wheels, the target luminance or select a colour from a colour picker by clicking the area below the individual wheels.
07. RGB Curves
The RGB Curves tab shows the RGB look-up tables that are used to balance the clip. You can directly modify the curves by clicking and dragging the spline points with the left mouse buttons. Let’s give that a try on our clip by clicking and dragging the green curve down to the right, what you may notice is even if the drop down tab is set to Chrominance it will automatically change to RGB. This is a useful tool for making minor adjustments per channel.
The offsets tab provides an overview of source and target colours. You can edit each value separately, either by entering a value with the keyboard, or by clicking and dragging inside the box. Enabling Gang will modify the Red, Green and Blue value of a row at the same time. Each row can also be reset individually with the Reset button.
Enabling Lock prevents further adjustment to a source or target colour. Make sure Lock is pressed for both Balance Point and Balance Target. Then click Balance Frame. Notice how all values have been re-sampled, except the locked Balance Point and Balance Target.
09. Colour Balance Presets
You can store the current parameters of the Colour Balance effect in an effect preset. This is really useful if you are working on a project that is displaying many similar colour fade and shifts across multiple shots.
Let’s go to the first frame of the clip and making sure we have our sampling dropdowns set to RGB click the Balance Frame button. Now we are going to click Store in the Presets panel on the right to create a new preset. Let’s edit the text edit box just underneath the thumbnail that has just been generated and call it chanti_balance.
Next let’s click the < button next to the clip thumbnail on the top left to jump to the second clip CHANTI_SHOT_001. Let’s create a Colour Balance effect for the second clip, select the preset and click Recall. Both clips now have their colour restored to the same standard.
In our next tutorial we will be learning how to remove dirt from a film scan using the powerful Auto Dirt Tool.