# necks

Python API: `luxonis_train.nodes.necks`

Necks that refine the feature maps of a backbone for a head.

 * [RepPANNeck](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/necks/reppan_neck/reppan_neck.md)
   fuses the feature maps of several scales. The detection, instance segmentation, and keypoint detection models use it.
 * [SVTRNeck](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/necks/svtr_neck/svtr_neck.md)
   refines the last feature map with SVTR transformer blocks. The OCR recognition model uses it.

## Child Pages

 * [reppan_neck](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/necks/reppan_neck.md)
 * [svtr_neck](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/necks/svtr_neck.md)