# Data Format¶

Finetuner uses Jina Document as the primitive data type. In particular, DocumentArray and DocumentArrayMemap are the input data type in the high-level finetuner.fit() API. This means, your training dataset and evaluation dataset should be stored in DocumentArray or DocumentArrayMemap, where each training or evaluation instance is a Document object:

import finetuner

finetuner.fit(model,
train_data=...,
eval_data=...)


This chapter introduces how to construct a Document in a way that Finetuner will accept.

There are three different types of datasets:

Tip

We recommend to keep the input DocumentArray as simple as possible, e.g. only fill essential fields such as .uri. The data loading and heavylifting work should be done via preprocess_fn in an on-demand manner.

Regardless of which dataset format we choose, all Documents need to have a non-empty .content attribute. Either you fill in DocumentArray.contents in advance, or load them on-demand.

When working with a big dataset, loading data on-demand is more favorable as you can not store your entire dataset into memory, . Moreover, you may want to apply random augmentations to images each time they are used in a batch, whereas you can’t prepare those augmentations in advance. For these purposes, you can use preprocess_fn argument of the Dataset. This argument is universally available from low-level ClassDataset and SessionDataset up to the top most level finetuner.fit API.

Let’s see some examples.

### Examples¶

#### Load image on the fly¶

Let’s start with an example of the first case - loading images on the fly. In this case we would have images stored on disk, and their paths stored in the .uri attribute of each Document. In preprocess_fn we would then load the image and return the numpy array.

import numpy as np
from finetuner import fit
from jina import Document, DocumentArray

dataset = DocumentArray([
Document(uri='path/to/image.jpg', tags={'finetuner_label': 1}}),
# ...
])

return d.blob

model = ...


#### Image augmentation¶

Next, let’s take a look at an example where we apply some basic image augmentation. We’ll be using the albumentations library for image augmentation in this example

import albumentations as A
import numpy as np
from finetuner import fit
from jina import Document, DocumentArray

dataset = DocumentArray([
Document(blob=np.random.rand(3, 128, 128), tags={'finetuner_label': 1}}),
# ...
])

def augment_image(doc: Document) -> np.ndarray:
transform = A.Compose([
A.HorizontalFlip(p=0.5),
A.RandomBrightnessContrast(p=0.2),
])

return transform(image=doc.blob)['image']

model = ...
fit(model, train_data=dataset, preprocess_fn=augment_image)