# How To: Normalized Coordinates of the Bounding Box `[ymin, xmin, ymax, xmax] for TFDS, TensorFlow`

#tfds.features.BBoxFeature

TFDS BBoxFeature uses normalized coordinates.

## What is the normalized coordinates then?

Normalized device coordinate or NDC space is a screen independent display coordinate system; it encompasses a cube where the *x, y*, and *z* components range from −1 to 1.

## An example for xmin, ymin, xmax, ymax

The bounding box has the following `(x, y)`

coordinates of its corners: top-left is `(x_min, y_min)`

or `(98px, 345px)`

, top-right is `(x_max, y_min)`

or `(420px, 345px)`

, bottom-left is `(x_min, y_max)`

or `(98px, 462px)`

, bottom-right is `(x_max, y_max)`

or `(420px, 462px)`

. As you see, coordinates of the bounding box's corners are calculated with respect to the top-left corner of the image which has `(x, y)`

coordinates `(0, 0)`

.

# pascal_voc

`pascal_voc`

is a format used by the Pascal VOC dataset. Coordinates of a bounding box are encoded with four values in pixels: `[x_min, y_min, x_max, y_max]`

. `x_min`

and `y_min`

are coordinates of the top-left corner of the bounding box. `x_max`

and `y_max`

are coordinates of bottom-right corner of the bounding box.

Coordinates of the example bounding box in this format are `[98, 345, 420, 462]`

.

# albumentations

`albumentations`

is similar to `pascal_voc`

, because it also uses four values `[x_min, y_min, x_max, y_max]`

to represent a bounding box. But unlike `pascal_voc`

, **albumentations**** uses normalized values**. To normalize values, we **divide coordinates in pixels **for the x- and y-axis by the width and the height of the image.

*Coordinates of the example bounding box in this format are **[98 / 640, 345 / 480, 420 / 640, 462 / 480]** which are **[0.153125, 0.71875, 0.65625, 0.9625]**.*

Albumentations uses this format internally to work with bounding boxes and augment them.