# Keyframe Interpolation
Interpolation of an annotation is a process of labelling a moving object by the tool estimating its position across frames between two defined frames. These frames in which the user sets the position of the annotation are called Keyframes. A keyframe can also be created with the `Shortcut K`.
On creating a keyframe, the tool automatically calculates and repositions the annotations in the interim frames between defined keyframes.
The keyframes are visible on the timeline (blue line under the frames) for a given selected annotation indicating that the position was set by the annotators themselves in those frames.
For instance, in the example below, the object was in motion from Frame 1 to Frame 25 and moved out of the scene. `Frame 1, 5, 10, 15 & 25` are keyframes where the annotator manually set the annotation positions, while the intermediate frames have positions calculated by the tool.
{% hint style="success" %} To remove a keyframe or bring the annotation back to the tool-calculated position, visit the frame and press `K` provided the annotation was selected in the prior frame.
{% endhint %}
## Benefits
* **Efficiency:** Reduces the time and effort required to annotate frames individually by automatically propagating annotations across intermediate frames.
* **Consistency:** Ensures uniformity in annotations across sequential frames, minimizing discrepancies and improving accuracy.
***
## Steps to use Keyframe Interpolation
Keyframe Interpolation is used for labelling object(s) in motion. Once a moving object has been identified, the process for Keyframe Interpolation can begin.
{% stepper %}
{% step %}
### Identify the best frame
Identify the frame where the object is most clearly visible — often the frame where the object is closest to the ego vehicle.
{% endstep %}
{% step %}
### Create the annotation
Create the annotation for the object in that frame. Modify its dimensions to annotate accurately and provide the attribute values.
* The first time the annotation is created, it inherently becomes a Keyframe.
{% endstep %}
{% step %}
### Propagation
The annotation is propagated across all frames (forward and backward) on the same world coordinates (provided the ego pose data is available in the dataset).
{% endstep %}
{% step %}
### Track and reposition
Track the object by navigating in one direction. After approximately 5–7 frames from the initial frame, reposition the annotation on the object accurately.
* As soon as the cuboid is repositioned, the current frame becomes a Keyframe.
* The tool automatically adjusts the positions of all annotations between the two Keyframes.
{% endstep %}
{% step %}
### Repeat until object leaves scene
Repeat this process until the object is no longer visible in the sequence.
{% endstep %}
{% step %}
### Deleting annotation and resulting keyframes
Deleting the annotation in any frame will make the immediate next/previous frame a keyframe where the annotation is present.
{% endstep %}
{% step %}
Examples:
* The object is available between `Frame 1–9` and not visible on `Frame 10`. The annotation is created on `Frame 1`. If the annotation is deleted from `Frame 10`, then `Frame 9` becomes a Keyframe.
* The object is available between `Frame 11–14` and leaves the scene. The annotation is created on `Frame 11`. If the annotation is deleted from `Frame 15` onwards, then `Frame 14` becomes a Keyframe.
{% endstep %}
{% endstepper %}
***
## Adding Keyframes
A frame turns into a Keyframe when the user does any of the following:
* Creates an annotation on any frame.
* Makes any position modification to an annotation manually.
* Deletes the annotation on a frame which makes the immediate next and/or previous frames the annotation occurs in a Keyframe.
* Uses the `Shortcut K` while an annotation is selected. This makes the frame a Keyframe without making any changes to the positioning of the annotation.
{% hint style="success" %} This is useful when the object is both stationary and moving across frames.
{% endhint %}
Example workflow:
* An object is stationary from `Frame 1–10` and starts moving on `Frame 11`.
* Create the annotation on `Frame 1` - it propagates across frames in the same position.
* On `Frame 10` press `K` to mark it as a Keyframe.
* On `Frame 11` reposition the annotation where the object has started to move - `Frame 11` becomes a Keyframe.
By adding the Keyframe on `Frame 10`, the tool is prevented from interpolating the annotation beyond `Frame 1–11`.
***
## Removing a Keyframe
Keyframes can be removed by selecting an annotation on a keyframe and pressing the `Shortcut K`. This shortcut toggles adding and removing a Keyframe.
## Label Occluded Objects
When an object is occluded in interim frames, follow these steps:
{% stepper %}
{% step %}
### Create the annotation on the object
Create the annotation on the object (e.g., `Frame 1`).
{% endstep %}
{% step %}
### Mark a keyframe before occlusion
Go to the frame where the object is visible just before occlusion (e.g., `Frame 8`) and press `K` to make it a Keyframe.
{% endstep %}
{% step %}
### Delete annotation for occluded range
Go to the frame where the object reappears (e.g., `Frame 12`).
* Right-click on the selected annotation and choose the option to `Delete` annotation between a frame range.
* Select the frame range (e.g., `Frame 9 - 11`) and apply the action.
The annotation will be deleted from this range without re-positioning it in frames that were not Keyframes.
{% endstep %}
{% endstepper %}
To remove a keyframe or bring the annotation back to the tool-calculated position, visit the frame and press `K` provided the annotation was selected in the prior frame.
{% endhint %}
## Benefits
* **Efficiency:** Reduces the time and effort required to annotate frames individually by automatically propagating annotations across intermediate frames.
* **Consistency:** Ensures uniformity in annotations across sequential frames, minimizing discrepancies and improving accuracy.
***
## Steps to use Keyframe Interpolation
Keyframe Interpolation is used for labelling object(s) in motion. Once a moving object has been identified, the process for Keyframe Interpolation can begin.
{% stepper %}
{% step %}
### Identify the best frame
Identify the frame where the object is most clearly visible — often the frame where the object is closest to the ego vehicle.
{% endstep %}
{% step %}
### Create the annotation
Create the annotation for the object in that frame. Modify its dimensions to annotate accurately and provide the attribute values.
* The first time the annotation is created, it inherently becomes a Keyframe.
{% endstep %}
{% step %}
### Propagation
The annotation is propagated across all frames (forward and backward) on the same world coordinates (provided the ego pose data is available in the dataset).
{% endstep %}
{% step %}
### Track and reposition
Track the object by navigating in one direction. After approximately 5–7 frames from the initial frame, reposition the annotation on the object accurately.
* As soon as the cuboid is repositioned, the current frame becomes a Keyframe.
* The tool automatically adjusts the positions of all annotations between the two Keyframes.
{% endstep %}
{% step %}
### Repeat until object leaves scene
Repeat this process until the object is no longer visible in the sequence.
{% endstep %}
{% step %}
### Deleting annotation and resulting keyframes
Deleting the annotation in any frame will make the immediate next/previous frame a keyframe where the annotation is present.
{% endstep %}
{% step %}
Examples:
* The object is available between `Frame 1–9` and not visible on `Frame 10`. The annotation is created on `Frame 1`. If the annotation is deleted from `Frame 10`, then `Frame 9` becomes a Keyframe.