# DML_ROI_ALIGN_OPERATOR_DESC structure (directml.h)

Performs an ROI Align operation, as described in the Mask R-CNN paper. In summary, the operation extracts crops from the input image tensor and resizes them to a common output size specified by the last 2 dimensions of *OutputTensor* using the specified *InterpolationMode*.

Important

This API is available as part of the DirectML standalone redistributable package (see Microsoft.AI.DirectML. Also see DirectML version history.

## Syntax

```
struct DML_ROI_ALIGN_OPERATOR_DESC
{
const DML_TENSOR_DESC* InputTensor;
const DML_TENSOR_DESC* ROITensor;
const DML_TENSOR_DESC* BatchIndicesTensor;
const DML_TENSOR_DESC* OutputTensor;
DML_REDUCE_FUNCTION ReductionFunction;
DML_INTERPOLATION_MODE InterpolationMode;
FLOAT SpatialScaleX;
FLOAT SpatialScaleY;
FLOAT OutOfBoundsInputValue;
UINT MinimumSamplesPerOutput;
UINT MaximumSamplesPerOutput;
};
```

## Members

`InputTensor`

Type: **const DML_TENSOR_DESC***

A tensor containing the input data with dimensions `{ BatchCount, ChannelCount, InputHeight, InputWidth }`

.

`ROITensor`

Type: **const DML_TENSOR_DESC***

A tensor containing the regions of interest (ROI) data. The allowed dimensions of `ROITensor`

are `{ NumROIs, 4 }`

, `{ 1, NumROIs, 4 }`

, or `{ 1, 1, NumROIs, 4 }`

. For each ROI, the values will be the coordinates of its top-left and bottom-right corners in the order `[x1, y1, x2, y2]`

.

`BatchIndicesTensor`

Type: **const DML_TENSOR_DESC***

A tensor containing the batch indices to extract the ROIs from. The allowed dimensions of `BatchIndicesTensor`

are `{ NumROIs }`

, `{ 1, NumROIs }`

, `{ 1, 1, NumROIs }`

, or `{ 1, 1, 1, NumROIs }`

. Each value is the index of a batch from *InputTensor*. The behavior is undefined if the values are not in the range [0, BatchCount).

`OutputTensor`

Type: **const DML_TENSOR_DESC***

A tensor containing the output data. The expected dimensions of *OutputTensor* are `{ NumROIs, ChannelCount, OutputHeight, OutputWidth }`

.

`ReductionFunction`

Type: **DML_REDUCE_FUNCTION**

The reduction function to use when reducing across all input samples that contribute to an output element (DML_REDUCE_FUNCTION_AVERAGE or **DML_REDUCE_FUNCTION_MAX**). The number of input samples to reduce across is bounded by *MinimumSamplesPerOutput* and *MaximumSamplesPerOutput*.

`InterpolationMode`

Type: **DML_INTERPOLATION_MODE**

The interpolation mode to use when resizing the regions.

- DML_INTERPOLATION_MODE_NEAREST_NEIGHBOR. Uses the
*Nearest Neighbor*algorithm, which chooses the input element nearest to the corresponding pixel center for each output element. **DML_INTERPOLATION_MODE_LINEAR**. Uses the*Bilinear*algorithm, which computes the output element by doing the weighted average of the 2 nearest neighboring input elements per dimension. Since only 2 dimensions are resized, the weighted average is computed on a total of 4 input elements for each output element.

`SpatialScaleX`

Type: **FLOAT**

The X (or width) component of the scaling factor to multiply the *ROITensor* coordinates by in order to make them proportionate to *InputHeight* and *InputWidth*. For example, if *ROITensor* contains normalized coordinates (values in the range [0..1]), then *SpatialScaleX* would usually have the same value as *InputWidth*.

`SpatialScaleY`

Type: **FLOAT**

The Y (or height) component of the scaling factor to multiply the *ROITensor* coordinates by in order to make them proportionate to *InputHeight* and *InputWidth*. For example, if *ROITensor* contains normalized coordinates (values in the range [0..1]), *SpatialScaleY* would usually have the same value as *InputHeight*.

`OutOfBoundsInputValue`

Type: **FLOAT**

The value to read from *InputTensor* when the ROIs are outside the bounds of *InputTensor*. This can happen when the values obtained after scaling *ROITensor* by *SpatialScaleX* and *SpatialScaleY* are bigger than *InputWidth* and *InputHeight*.

`MinimumSamplesPerOutput`

Type: **UINT**

The minimum number of input samples to use for every output element. The operator will calculate the number of input samples by doing `ScaledCropSize / OutputSize`

, and then clamp it to *MinimumSamplesPerOutput* and *MaximumSamplesPerOutput*.

`MaximumSamplesPerOutput`

Type: **UINT**

The maximum number of input samples to use for every output element. The operator will calculate the number of input samples by doing `ScaledCropSize / OutputSize`

, and then clamp it to *MinimumSamplesPerOutput* and *MaximumSamplesPerOutput*.

## Availability

This operator was introduced in `DML_FEATURE_LEVEL_3_0`

.

## Tensor constraints

*InputTensor*, *OutputTensor*, and *ROITensor* must have the same *DataType*.

## Tensor support

Tensor | Kind | Supported dimension counts | Supported data types |
---|---|---|---|

InputTensor | Input | 4 | FLOAT32, FLOAT16 |

ROITensor | Input | 2 to 4 | FLOAT32, FLOAT16 |

BatchIndicesTensor | Input | 1 to 4 | UINT32 |

OutputTensor | Output | 4 | FLOAT32, FLOAT16 |

## Requirements

Header |
directml.h |