MinMaxObserver

class torch.quantization.observer.MinMaxObserver(dtype=torch.quint8, qscheme=torch.per_tensor_affine, reduce_range=False, quant_min=None, quant_max=None, factory_kwargs=None, memoryless=False)

Observer module for computing the quantization parameters based on the running min and max values.

This observer uses the tensor min/max statistics to compute the quantization parameters. The module records the running minimum and maximum of incoming tensors, and uses this statistic to compute the quantization parameters.

Parameters

• dtype – Quantized data type

• qscheme – Quantization scheme to be used

• reduce_range – Reduces the range of the quantized data type by 1 bit

• quant_min – Minimum quantization value. If unspecified, it will follow the 8-bit setup.

• quant_max – Maximum quantization value. If unspecified, it will follow the 8-bit setup.

Given running min/max as $x_\text{min}$ and $x_\text{max}$, scale $s$ and zero point $z$ are computed as:

The running minimum/maximum $x_\text{min/max}$ is computed as:

$$\begin{array}{ll} x_\text{min} &= \begin{cases} \min(X) & \text{if~}x_\text{min} = \text{None} \\ \min\left(x_\text{min}, \min(X)\right) & \text{otherwise} \end{cases}\\ x_\text{max} &= \begin{cases} \max(X) & \text{if~}x_\text{max} = \text{None} \\ \max\left(x_\text{max}, \max(X)\right) & \text{otherwise} \end{cases}\\ \end{array}$$

where $X$ is the observed tensor.

The scale $s$ and zero point $z$ are then computed as:

$$\begin{aligned} \text{if Symmetric:}&\\ &s = 2 \max(|x_\text{min}|, x_\text{max}) / \left( Q_\text{max} - Q_\text{min} \right) \\ &z = \begin{cases} 0 & \text{if dtype is qint8} \\ 128 & \text{otherwise} \end{cases}\\ \text{Otherwise:}&\\ &s = \left( x_\text{max} - x_\text{min} \right ) / \left( Q_\text{max} - Q_\text{min} \right ) \\ &z = Q_\text{min} - \text{round}(x_\text{min} / s) \end{aligned}$$

where $Q_\text{min}$ and $Q_\text{max}$ are the minimum and maximum of the quantized data type.

Warning

Only works with torch.per_tensor_symmetric quantization scheme

Warning

dtype can only take torch.qint8 or torch.quint8.

Note

If the running minimum equals to the running maximum, the scale and zero_point are set to 1.0 and 0.

calculate_qparams()

Calculates the quantization parameters.

forward(x_orig)

Records the running minimum and maximum of x.

reset_min_max_vals()

Resets the min/max values.