Image properties (shape, dtype, size) in Computer Vision - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the shape property of an image represent?

The shape property shows the dimensions of the image, usually as (height, width, channels). It tells how tall, wide, and how many color channels the image has.

beginner

What is dtype in the context of an image?

dtype means the data type of the image pixels, like uint8 for values 0-255 or float32 for decimal values. It affects how pixel values are stored and processed.

beginner

How do you find the total number of pixels in an image?

Multiply the height by the width of the image. For example, an image with shape (100, 200) has 100 × 200 = 20,000 pixels.

intermediate

What does the size property of an image tell you?

size gives the total number of elements (pixels × channels) in the image array. For example, a 100×200 RGB image has size 100 × 200 × 3 = 60,000.

intermediate

Why is knowing the dtype important when working with images?

Because it affects memory use and how pixel values are interpreted. For example, uint8 stores integers 0-255, while float32 can store decimals, which is important for some image processing tasks.

What does the shape (64, 64, 3) of an image mean?

A 64 pixels total with 3 channels

B Width 64, height 64, 3 color channels

C 3 images of size 64x64

D Height 64, width 64, 3 color channels

The shape is (height, width, channels), so 64 height, 64 width, and 3 color channels (like RGB).

If an image has dtype uint8, what is the range of pixel values?

A -128 to 127

B 0 to 1

C 0 to 255

D Any decimal number

uint8 means unsigned 8-bit integers, so pixel values range from 0 to 255.

How do you calculate the total number of pixels in an image?

A Multiply height by width

B Add height and width

C Multiply channels by width

D Divide height by width

Total pixels = height × width.

What does the size property of an image array represent?

A Number of color channels

B Total number of elements (pixels × channels)

C Width of the image

D Height of the image

Size is the total number of elements in the array, including all pixels and channels.

Why might you convert an image's dtype from uint8 to float32?

A To allow decimal pixel values for precise calculations

B To reduce memory usage

C To increase pixel value range to 0-65535

D To make the image grayscale

float32 allows decimal values, useful for some image processing and neural network inputs.

Explain what the shape, dtype, and size properties of an image tell you.

Think about how these properties describe the image's structure and data.

Describe why understanding image properties is important before processing images in machine learning.

Consider how these properties affect model training and predictions.