Note
Click here to download the full example code
Writing Custom Computer Vision Checks#
Deepchecks offers a wide range of checks for computer vision problems, addressing distribution issues, performance checks and more. Nevertheless, in order to fully validate your ML pipeline you often need to write your own checks. This guide will walk you through the basics of writing your own checks.
We recommend writing a single check for each aspect of the model or data you would like to validate. As explained in Deepchecks Hierarchy, the role of the check is to run the logic and output a display and a pythonic value. Then, a condition can be defined on that value to determine if the check is successful or not.
Vision Checks Structure#
The first step when writing a vision check is to decide what check base class to use. You can read more in the
Base Checks Types section. In this case, we wish to compare train and test dataset, so we select the
TrainTestBaseCheck. This type of check must implement the following three methods:
initialize_run - Actions to be performed before starting to iterate over the dataloader batches.
update - Actions to be performed on each batch.
compute - Actions to be performed after iterating over all the batches. Returns the check display and the return value.
While ModelOnlyCheck alone do not implement the update method. Apart from that, the check init should recipient and handle check parameters.
Write a Basic Check#
Let’s implement a simple check, comparing the average of each color channel between the train and the test dataset.
We’ll start by writing the simplest possible example, returning only a dict of the color averages. We’ll use external functions when implementing the check in order to be able to reuse them later.
Good to know: the return value of a check can be any object, a number, dictionary, string, etc…
The Context and Batch Objects#
The three methods of the vision check - initialize_run, update and compute, make use of the Context object and the Batch object.
The context object contains the basic objects deepchecks uses - the train and test VisionData objects, and the use model itself. The Batch objects contains processed data from the dataloader, such as the images, labels and model predictions. For some checks, such as the one shown in this example, the Context object is not needed.
For more examples of using the Context and Batch objects for different types of base checks, see the Custom Check Templates guide.
Check Example#
import typing as t
import numpy as np
from deepchecks.core.check_result import CheckResult
from deepchecks.core.checks import DatasetKind
from deepchecks.core.condition import ConditionCategory
from deepchecks.vision.base_checks import TrainTestCheck
from deepchecks.vision.batch_wrapper import Batch
from deepchecks.vision.context import Context
def init_color_averages_dict() -> t.Dict[str, np.array]:
"""Initialize the color averages dicts."""
return {
DatasetKind.TRAIN.value: np.zeros((3,), dtype=np.float64),
DatasetKind.TEST.value: np.zeros((3,), dtype=np.float64),
}
def init_pixel_counts_dict() -> t.Dict[str, int]:
"""Initialize the pixel counts dicts."""
return {
DatasetKind.TRAIN.value: 0,
DatasetKind.TEST.value: 0,
}
def sum_pixel_values(batch: Batch) -> np.array:
"""Sum the values of all the pixels in the batch, returning a numpy array with an entry per channel."""
images = batch.images
return sum(image.sum(axis=(0, 1)) for image in images) # sum over the batch and pixels
def count_pixels_in_batch(batch: Batch) -> int:
"""Count the pixels in the batch."""
return sum((image.shape[0] * image.shape[1] for image in batch.images))
class ColorAveragesCheck(TrainTestCheck):
"""Check if the average of each color channel is the same between the train and test dataset."""
def __init__(self, channel_names: t.Tuple[str] = None):
"""Init the check and enable customization of the channel_names."""
super().__init__()
if channel_names is None:
self.channel_names = ('R', 'G', 'B')
def initialize_run(self, context: Context):
"""Initialize the color_averages dict and pixel counter dict."""
self._color_averages = init_color_averages_dict()
self._pixel_count = init_pixel_counts_dict()
def update(self, context: Context, batch: Batch, dataset_kind: DatasetKind):
"""Add the batch color counts to the color_averages dict, and update counter."""
self._color_averages[dataset_kind.value] += sum_pixel_values(batch) # add to the color_averages dict
# count the number of pixels we have summed
self._pixel_count[dataset_kind.value] += count_pixels_in_batch(batch)
def compute(self, context: Context):
"""Compute the color averages and return them."""
# Divide by the number of pixels to get the average pixel value per color channel
for dataset_kind in DatasetKind:
self._color_averages[dataset_kind.value] /= self._pixel_count[dataset_kind.value]
# Return the color averages in a dict by channel name
return_value = {d_kind: dict(zip(self.channel_names, color_averages))
for d_kind, color_averages in self._color_averages.items()}
return CheckResult(return_value)
Hooray! we just implemented a custom check. To read more about the internal objects Let’s run it and see what happens:
from deepchecks.vision.datasets.detection.coco import load_dataset
train_ds = load_dataset(train=True, object_type='VisionData')
test_ds = load_dataset(train=False, object_type='VisionData')
result = ColorAveragesCheck().run(train_ds, test_ds)
result
Validating Input:
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Computing Check:
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Computing Check:
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Our check ran successfully, but we got the print “Nothing found”. This is because we haven’t defined to the check anything to display, so the default behavior is to print “Nothing found”. In order to access the value that we have defined earlier we can use the “value” property on the result.
result.value
{'Train': {'R': 120.59282480343832, 'G': 117.66383923861159, 'B': 102.58390542973886}, 'Test': {'R': 114.69132386085319, 'G': 107.46618940457067, 'B': 97.39751220459796}}
favorite checks from our API ref.
Check Display#
Most of the times we will want our checks to have a visual display that will quickly summarize the check result. We can pass objects for display to the CheckResult. Objects for display should be of type: html string, dataframe or a function that plots a graph. Let’s define a graph that will be displayed using Plotly. We will inherit from the original check to shorten the code an update only the compute method.
Good to know: ``display`` can receive a single object to display or a list of objects
import pandas as pd
import plotly.express as px
class ColorAveragesCheck(TrainTestCheck):
"""Check if the average of each color channel is the same between the train and test dataset."""
def __init__(self, channel_names: t.Tuple[str] = None):
"""Init the check and enable customization of the channel_names."""
super().__init__()
if channel_names is None:
self.channel_names = ('R', 'G', 'B')
def initialize_run(self, context: Context):
"""Initialize the color_averages dict and pixel counter dict."""
self._color_averages = init_color_averages_dict()
self._pixel_count = init_pixel_counts_dict()
def update(self, context: Context, batch: Batch, dataset_kind: DatasetKind):
"""Add the batch color counts to the color_averages dict, and update counter."""
self._color_averages[dataset_kind.value] += sum_pixel_values(batch) # add to the color_averages dict
# count the number of pixels we have summed
self._pixel_count[dataset_kind.value] += count_pixels_in_batch(batch)
def compute(self, context: Context):
"""Compute the color averages and return them. Also display a histogram comparing train and test."""
# Divide by the number of pixels to get the average pixel value per color channel
for dataset_kind in DatasetKind:
self._color_averages[dataset_kind.value] /= self._pixel_count[dataset_kind.value]
# Return the color averages in a dict by channel name
return_value = {d_kind: dict(zip(self.channel_names, color_averages))
for d_kind, color_averages in self._color_averages.items()}
# **New Code Here**!!!
# ========================
# Display a histogram comparing train and test
color_averages_df = pd.DataFrame(return_value).unstack().reset_index()
color_averages_df.columns = ['Dataset', 'Channel', 'Pixel Value']
fig = px.histogram(color_averages_df, x='Dataset', y='Pixel Value', color='Channel', barmode='group',
histfunc='avg', color_discrete_sequence=['rgb(255,0,0)', 'rgb(0,255,0)', 'rgb(0,0,255)'],
title='Color Averages Histogram')
return CheckResult(return_value, display=[fig])
Let check it out:
result = ColorAveragesCheck().run(train_ds, test_ds)
result
Validating Input:
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Validating Input:
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Ingesting Batches - Train Dataset:
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Computing Check:
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Voilà! Now we have a check that prints a graph and has a value. We can add this check to any Suite, and it will run within it.
Defining a Condition#
Finally, we can add a condition to our check. A condition is a function that receives the result of the check and returns a condition result object. To read more on conditions, check out the condition user guide. In this case, we’ll define a condition verifying that the color averages haven’t changed by more than 10%.
from deepchecks.core import ConditionResult
class ColorAveragesCheck(TrainTestCheck):
"""Check if the average of each color channel is the same between the train and test dataset."""
def __init__(self, channel_names: t.Tuple[str] = None):
"""Init the check and enable customization of the channel_names."""
super().__init__()
if channel_names is None:
self.channel_names = ('R', 'G', 'B')
def initialize_run(self, context: Context):
"""Initialize the color_averages dict and pixel counter dict."""
self._color_averages = init_color_averages_dict()
self._pixel_count = init_pixel_counts_dict()
def update(self, context: Context, batch: Batch, dataset_kind: DatasetKind):
"""Add the batch color counts to the color_averages dict, and update counter."""
self._color_averages[dataset_kind.value] += sum_pixel_values(batch) # add to the color_averages dict
# count the number of pixels we have summed
self._pixel_count[dataset_kind.value] += count_pixels_in_batch(batch)
def compute(self, context: Context):
"""Compute the color averages and return them. Also display a histogram comparing train and test."""
# Divide by the number of pixels to get the average pixel value per color channel
for dataset_kind in DatasetKind:
self._color_averages[dataset_kind.value] /= self._pixel_count[dataset_kind.value]
# Return the color averages in a dict by channel name
return_value = {d_kind: dict(zip(self.channel_names, color_averages))
for d_kind, color_averages in self._color_averages.items()}
# Display a histogram comparing train and test
color_averages_df = pd.DataFrame(return_value).unstack().reset_index()
color_averages_df.columns = ['Dataset', 'Channel', 'Pixel Value']
fig = px.histogram(color_averages_df, x='Dataset', y='Pixel Value', color='Channel', barmode='group',
histfunc='avg', color_discrete_sequence=['rgb(255,0,0)', 'rgb(0,255,0)', 'rgb(0,0,255)'],
title='Color Averages Histogram')
return CheckResult(return_value, display=[fig])
# **New Code Here**!!!
# ========================
def add_condition_color_average_change_not_greater_than(self, change_ratio: float = 0.1) -> ConditionResult:
"""Add a condition verifying that the color averages haven't changed by more than change_ratio%."""
def condition(check_result: CheckResult) -> ConditionResult:
failing_channels = []
# Iterate over the color averages and verify that they haven't changed by more than change_ratio
for channel in check_result.value[DatasetKind.TRAIN.value].keys():
if abs(check_result.value[DatasetKind.TRAIN.value][channel] -
check_result.value[DatasetKind.TEST.value][channel]) > change_ratio:
failing_channels.append(channel)
# If there are failing channels, return a condition result with the failing channels
if failing_channels:
return ConditionResult(ConditionCategory.FAIL, f'The color averages have changes by more than threshold in the channels'
f' {failing_channels}.')
else:
return ConditionResult(ConditionCategory.PASS)
return self.add_condition(f'Change in color averages not greater than {change_ratio:.2%}', condition)
Let check it out:
result = ColorAveragesCheck().run(train_ds, test_ds)
result
Validating Input:
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Validating Input:
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Ingesting Batches - Train Dataset:
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Computing Check:
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Computing Check:
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And now our check we will alert us automatically if the color averages have changed by more than 10%!
Base Checks Types#
Vision checks all inherit from one of the following classes:
SingleDatasetCheck- Check that runs on a single dataset and model.TrainTestCheck- Check that runs on a train and test dataset and model.ModelOnlyCheck- Check that runs on only a model .
All three classes inherit from the BaseCheck BaseCheck, same as checks in any other
deepchecks subpackage. Each has its own run signature, according to the objects on which it will run.
The first two classes of checks run some logic on the image data, and so the check structure is designed to enable accumulating and computation on batches outputted by the dataloader.
Total running time of the script: ( 0 minutes 5.502 seconds)