doctr.transforms

Data transformations are part of both training and inference procedure. Drawing inspiration from the design of torchvision, we express transformations as composable modules.

Supported transformations

Here are all transformations that are available through docTR:

class Resize(

size,

interpolation=F.InterpolationMode.BILINEAR,

preserve_aspect_ratio=False,

symmetric_pad=False,

return_padding_mask=False,

)

Resize the input image to the given size

>>> import torch
>>> from doctr.transforms import Resize
>>> from doctr.utils import Sample
>>> transfo = Resize((64, 64), preserve_aspect_ratio=True, symmetric_pad=True)
>>> out = transfo(Sample(image=torch.rand((3, 64, 64))))

Parameters:

• size (int | tuple[int, int]) – output size in pixels, either a tuple (height, width) or a single integer for square images

• interpolation – interpolation mode to use for resizing, default is bilinear

• preserve_aspect_ratio (bool) – whether to preserve the aspect ratio of the image, if True, the image will be resized to fit within the target size while maintaining its aspect ratio

• symmetric_pad (bool) – whether to symmetrically pad the image to the target size, if True, the image will be padded equally on both sides to fit the target size

• return_padding_mask (bool) – whether to return a boolean mask alongside the image, with True on valid (image content) pixels and False on padded areas. This matches how masks propagate through the other transforms (padding and rotation fill new areas with False).

class GaussianNoise(mean=0.0, std=1.0)

Adds Gaussian Noise to the input tensor

>>> import torch
>>> from doctr.transforms import GaussianNoise
>>> from doctr.utils import Sample
>>> transfo = GaussianNoise(0., 1.)
>>> out = transfo(Sample(image=torch.rand((3, 224, 224))))

Parameters:

• mean (float) – mean of the gaussian distribution

• std (float) – std of the gaussian distribution

class ChannelShuffle

Randomly shuffle channel order of a given image

>>> import torch
>>> from doctr.transforms import ChannelShuffle
>>> from doctr.utils import Sample
>>> transfo = ChannelShuffle()
>>> out = transfo(Sample(image=torch.rand((3, 224, 224))))

class RandomHorizontalFlip(p=0.5)

Randomly flip the input image horizontally

>>> import torch
>>> from doctr.transforms import RandomHorizontalFlip
>>> from doctr.utils import Sample
>>> transfo = RandomHorizontalFlip(p=1.0)
>>> out = transfo(Sample(image=torch.rand((3, 224, 224)), target=np.array([[0.1, 0.2, 0.3, 0.4]])))

class RandomShadow(opacity_range=None)

Adds random shade to the input image

>>> import torch
>>> from doctr.transforms import RandomShadow
>>> from doctr.utils import Sample
>>> transfo = RandomShadow((0., 1.))
>>> out = transfo(Sample(image=torch.rand((3, 64, 64))))

Parameters:

opacity_range (tuple[float, float] | None) – minimum and maximum opacity of the shade

class RandomResize(

scale_range=(0.3, 0.9),

preserve_aspect_ratio=False,

symmetric_pad=False,

p=0.5,

)

Randomly resize the input image and align corresponding targets

>>> import torch
>>> from doctr.transforms import RandomResize
>>> from doctr.utils import Sample
>>> transfo = RandomResize((0.3, 0.9), preserve_aspect_ratio=True, symmetric_pad=True, p=0.5)
>>> out = transfo(Sample(image=torch.rand((3, 64, 64))))

Parameters:

• scale_range (tuple[float, float]) – range of the resizing factor for width and height (independently)

• preserve_aspect_ratio (bool | float) – whether to preserve the aspect ratio of the image,

• value (given a float)

• probability (the symmetric padding will be applied with this)

• symmetric_pad (bool | float) – whether to symmetrically pad the image,

• value

• probability

• p (float) – probability to apply the transformation

Composing transformations

It is common to require several transformations to be performed consecutively.

class SampleCompose(transforms)

Implements a wrapper that will apply transformations sequentially on both image and target

>>> import numpy as np
>>> import torch
>>> from doctr.transforms import SampleCompose, ImageTransform, ColorInversion, RandomRotate
>>> from doctr.utils import Sample
>>> transfos = SampleCompose([ImageTransform(ColorInversion((32, 32))), RandomRotate(30)])
>>> out, out_boxes = transfos(Sample(image=torch.rand(8, 64, 64, 3), target=np.zeros((2, 4))))

Parameters:

transforms (list[Callable[[Sample], Sample]]) – list of transformation modules

class ImageTransform(transform)

Implements a transform wrapper to turn an image-only transformation into an image+target transform

>>> import torch
>>> from doctr.transforms import ImageTransform, ColorInversion
>>> from doctr.utils import Sample
>>> transfo = ImageTransform(ColorInversion((32, 32)))
>>> out = transfo(Sample(image=torch.rand(8, 64, 64, 3)))

Parameters:

transform (Callable[[Any], Any]) – the image transformation module to wrap

class ColorInversion(min_val=0.5)

Applies the following tranformation to a tensor (image or batch of images): convert to grayscale, colorize (shift 0-values randomly), and then invert colors

>>> import torch
>>> from doctr.transforms import ColorInversion
>>> from doctr.utils import Sample
>>> transfo = ColorInversion(min_val=0.6)
>>> out = transfo(Sample(image=torch.rand(8, 64, 64, 3)))

Parameters:

min_val (float) – range [min_val, 1] to colorize RGB pixels

class OneOf(transforms)

Randomly apply one of the input transformations

>>> import torch
>>> from doctr.transforms import OneOf, JpegQuality, Gamma
>>> from doctr.utils import Sample
>>> transfo = OneOf([JpegQuality(), Gamma()])
>>> out = transfo(Sample(image=torch.rand(1, 64, 64, 3)))

Parameters:

transforms (list[Callable[[Sample], Sample]]) – list of transformations, one only will be picked

class RandomApply(transform, p=0.5)

Apply with a probability p the input transformation

>>> import torch
>>> from doctr.transforms import RandomApply, Gamma
>>> from doctr.utils import Sample
>>> transfo = RandomApply(Gamma(), p=.5)
>>> out = transfo(Sample(image=torch.rand(1, 64, 64, 3), target=np.array([[0.1, 0.1, 0.9, 0.9]]), mask=None))

Parameters:

• transform (Callable[[Sample], Sample]) – transformation to apply

• p (float) – probability to apply

class RandomRotate(max_angle=5.0, expand=False)

Randomly rotate a tensor image and its boxes

>>> import torch
>>> from doctr.transforms import RandomRotate
>>> transfo = RandomRotate(max_angle=30, expand=True)
>>> out = transfo(Sample(image=torch.rand(1, 64, 64, 3), target=np.array([[0.1, 0.1, 0.9, 0.9]]), mask=None))

Parameters:

• max_angle (float) – maximum angle for rotation, in degrees. Angles will be uniformly picked in [-max_angle, max_angle]

• expand (bool) – whether the image should be padded before the rotation

class RandomCrop(scale=(0.08, 1.0), ratio=(0.75, 1.33))

Randomly crop a tensor image and its boxes

>>> import torch
>>> from doctr.transforms import RandomCrop
>>> from doctr.utils import Sample
>>> transfo = RandomCrop(scale=(0.5, 1.0), ratio=(0.75, 1.33))
>>> out = transfo(Sample(image=torch.rand(1, 64, 64, 3), target=np.array([[0.1, 0.1, 0.9, 0.9]]), mask=None))

Parameters:

• scale (tuple[float, float]) – tuple of floats, relative (min_area, max_area) of the crop

• ratio (tuple[float, float]) – tuple of float, relative (min_ratio, max_ratio) where ratio = h/w