Added
- Added **Image-related metrics**:
- Fréchet inception distance (FID) ([213](https://github.com/Lightning-AI/torchmetrics/pull/213))
- Kernel Inception Distance (KID) ([301](https://github.com/Lightning-AI/torchmetrics/pull/301))
- Inception Score ([299](https://github.com/Lightning-AI/torchmetrics/pull/299))
- KL divergence ([247](https://github.com/Lightning-AI/torchmetrics/pull/247))
- Added **Audio metrics**: SNR, SI_SDR, SI_SNR ([292](https://github.com/Lightning-AI/torchmetrics/pull/292))
- Added other metrics:
- Cosine Similarity ([305](https://github.com/Lightning-AI/torchmetrics/pull/305))
- Specificity ([210](https://github.com/Lightning-AI/torchmetrics/pull/210))
- Mean Absolute Percentage error (MAPE) ([248](https://github.com/Lightning-AI/torchmetrics/pull/248))
- Added `add_metrics` method to `MetricCollection` for adding additional metrics after initialization ([221](https://github.com/Lightning-AI/torchmetrics/pull/221))
- Added pre-gather reduction in the case of `dist_reduce_fx="cat"` to reduce communication cost ([217](https://github.com/Lightning-AI/torchmetrics/pull/217))
- Added better error message for `AUROC` when `num_classes` is not provided for multiclass input ([244](https://github.com/Lightning-AI/torchmetrics/pull/244))
- Added support for unnormalized scores (e.g. logits) in `Accuracy`, `Precision`, `Recall`, `FBeta`, `F1`, `StatScore`, `Hamming`, `ConfusionMatrix` metrics ([200](https://github.com/Lightning-AI/torchmetrics/pull/200))
- Added `squared` argument to `MeanSquaredError` for computing `RMSE` ([249](https://github.com/Lightning-AI/torchmetrics/pull/249))
- Added `is_differentiable` property to `ConfusionMatrix`, `F1`, `FBeta`, `Hamming`, `Hinge`, `IOU`, `MatthewsCorrcoef`, `Precision`, `Recall`, `PrecisionRecallCurve`, `ROC`, `StatScores` ([253](https://github.com/Lightning-AI/torchmetrics/pull/253))
- Added `sync` and `sync_context` methods for manually controlling when metric states are synced ([302](https://github.com/Lightning-AI/torchmetrics/pull/302))
Changed
- Forward cache is reset when `reset` method is called ([260](https://github.com/Lightning-AI/torchmetrics/pull/260))
- Improved per-class metric handling for imbalanced datasets for `precision`, `recall`, `precision_recall`, `fbeta`, `f1`, `accuracy`, and `specificity` ([204](https://github.com/Lightning-AI/torchmetrics/pull/204))
- Decorated `torch.jit.unused` to `MetricCollection` forward ([307](https://github.com/Lightning-AI/torchmetrics/pull/307))
- Renamed `thresholds` argument to binned metrics for manually controlling the thresholds ([322](https://github.com/Lightning-AI/torchmetrics/pull/322))
- Extend typing ([324](https://github.com/Lightning-AI/torchmetrics/pull/324),
[326](https://github.com/Lightning-AI/torchmetrics/pull/326),
[327](https://github.com/Lightning-AI/torchmetrics/pull/327))
Deprecated
- Deprecated `functional.mean_relative_error`, use `functional.mean_absolute_percentage_error` ([248](https://github.com/Lightning-AI/torchmetrics/pull/248))
- Deprecated `num_thresholds` argument in `BinnedPrecisionRecallCurve` ([322](https://github.com/Lightning-AI/torchmetrics/pull/322))
Removed
- Removed argument `is_multiclass` ([319](https://github.com/Lightning-AI/torchmetrics/pull/319))
Fixed
- AUC can also support more dimensional inputs when all but one dimension are of size 1 ([242](https://github.com/Lightning-AI/torchmetrics/pull/242))
- Fixed `dtype` of modular metrics after reset has been called ([243](https://github.com/Lightning-AI/torchmetrics/pull/243))
- Fixed calculation in `matthews_corrcoef` to correctly match formula ([321](https://github.com/Lightning-AI/torchmetrics/pull/321))
---