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Add a heatmap
=============
Heatmap is an optional [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) pipeline step. It is executed at each new gaze position to update heatmap image.
![Heatmap](../../img/heatmap.png)
## Enable and display ArFrame heatmap
[ArFrame.heatmap](../../argaze.md/#argaze.ArFeatures.ArFrame.heatmap) can be enabled thanks to a dedicated JSON entry.
Here is an extract from the JSON ArFrame configuration file where heatmap is enabled and displayed:
```json
{
"name": "My FullHD screen",
"size": [1920, 1080],
...
"heatmap": {
"size": [320, 180],
"sigma": 0.025,
"buffer": 0
},
...
"image_parameters": {
...
"heatmap_weight": 1
}
}
```
!!! note
[ArFrame.heatmap](../../argaze.md/#argaze.ArFeatures.ArFrame.heatmap) is automatically updated each time the [ArFrame.look](../../argaze.md/#argaze.ArFeatures.ArFrame.look) method is called. As explained in [visualisation chapter](visualisation.md), the resulting image is accessible thanks to [ArFrame.image](../../argaze.md/#argaze.ArFeatures.ArFrame.image) method.
Now, let's understand the meaning of each JSON entry.
### *size*
The heatmap image size in pixel. Higher size implies higher CPU load.
### *sigma*
The gaussian point spreading to draw at each gaze position.
![Point spread](../../img/point_spread.png)
### *buffer*
The size of point spread images buffer (0 means no buffering) to visualize only last N gaze positions.
### *heatmap_weight*
The weight of heatmap overlay in [ArFrame.image](../../argaze.md/#argaze.ArFeatures.ArFrame.image) between 0 and 1.
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