Losses API Reference

Factory Function

create_loss

def create_loss(loss_name: str, **kwargs) -> nn.Module

Create a loss function by name.

Available Losses:

Name	Description
combined	L1 + MSE + Gradient (default)
advanced	+ SSIM + SAM
spectral_focus	Higher SAM weight
spatial_focus	Higher Gradient/SSIM weight

Example:

from models import create_loss

criterion = create_loss('spectral_focus')
loss, loss_dict = criterion(pred, target)

---

Individual Loss Functions

GradientLoss

class GradientLoss(nn.Module):
    def __init__(self)

Computes L1 loss on image gradients for edge preservation.

loss_fn = GradientLoss()
loss = loss_fn(pred, target)  # Returns scalar

SpectralAngleLoss

class SpectralAngleLoss(nn.Module):
    def __init__(self, eps: float = 1e-8)

Spectral Angle Mapper (SAM) loss for spectral fidelity.

loss_fn = SpectralAngleLoss()
loss = loss_fn(pred, target)  # Returns scalar (radians)

SSIMLoss

class SSIMLoss(nn.Module):
    def __init__(self, window_size: int = 11)

Structural Similarity Index loss.

loss_fn = SSIMLoss()
loss = loss_fn(pred, target)  # Returns 1 - SSIM

PerceptualLoss

class PerceptualLoss(nn.Module):
    def __init__(self, layers: List[str] = None)

VGG-based perceptual loss using feature maps.

---

Combined Loss Functions

CombinedLoss

class CombinedLoss(nn.Module):
    def __init__(
        self,
        l1_weight: float = 1.0,
        mse_weight: float = 1.0,
        gradient_weight: float = 0.1
    )

Basic combined loss with L1, MSE, and gradient terms.

Returns: (total_loss, loss_dict)

loss_fn = CombinedLoss()
total_loss, loss_dict = loss_fn(pred, target)
# loss_dict = {'l1': ..., 'mse': ..., 'gradient': ..., 'total': ...}

AdvancedCombinedLoss

class AdvancedCombinedLoss(nn.Module):
    def __init__(
        self,
        l1_weight: float = 1.0,
        mse_weight: float = 1.0,
        gradient_weight: float = 0.1,
        ssim_weight: float = 0.1,
        sam_weight: float = 0.1,
        perceptual_weight: float = 0.0
    )

Advanced loss with all components configurable.

---

Loss Configurations

Default (combined)

{'l1': 1.0, 'mse': 1.0, 'gradient': 0.1}

Advanced

{'l1': 1.0, 'mse': 1.0, 'gradient': 0.1, 'ssim': 0.1, 'sam': 0.1}

Spectral Focus

{'l1': 1.0, 'mse': 0.5, 'gradient': 0.05, 'ssim': 0.1, 'sam': 0.5}

Spatial Focus

{'l1': 1.0, 'mse': 0.5, 'gradient': 0.2, 'ssim': 0.3, 'sam': 0.05}