Rotate

Overview

The Rotate sample demonstrates GPU-accelerated image rotation using CV-CUDA’s rotate operator. It reads an input image, computes a centring shift so the rotated content stays visible, and writes the result as a standard uint8 JPEG.

Usage

Basic Usage

Rotate the default tabby-cat image by 45 degrees:

python3 rotate.py

Custom Input

Rotate a specific image and save to a custom output path:

python3 rotate.py -i input.jpg -o cat_rotate.jpg

Command-Line Arguments

Argument

Short Form

Default

Description

--input

-i

tabby_tiger_cat.jpg

Input image file path

--output

-o

cvcuda/.cache/cat_rotate.jpg

Output image file path

Implementation

Centred Rotation

# cvcuda.rotate performs the inverse mapping:
#   src = R(angle) * (dst - shift)
# where R is a counter-clockwise rotation matrix (screen coords, y-down).
# To keep the image centre fixed we solve for the shift such that
# dst=(cx,cy) maps back to src=(cx,cy), giving:
#   shift = (cx*(1-cos) - cy*sin,  cy*(1-cos) + cx*sin)
h, w = input_image.shape[0], input_image.shape[1]
angle_deg = 45.0
angle_rad = math.radians(angle_deg)
cos_a = math.cos(angle_rad)
sin_a = math.sin(angle_rad)
cx, cy = w / 2.0, h / 2.0
shift_x = cx * (1 - cos_a) - cy * sin_a
shift_y = cy * (1 - cos_a) + cx * sin_a

Key points:

  1. Rotation origin: cvcuda.rotate rotates around the top-left corner, so a compensating translation shift must be provided to keep the image content centred.

  2. Centring shift: The shift (cx - cx*cos - cy*sin, cy - cy*cos + cx*sin) is derived from the standard 2-D rotation-about-centre formula.

  3. Interpolation: cvcuda.Interp.LINEAR gives smooth results; NEAREST is faster and CUBIC provides higher quality at the cost of more computation.

  4. Output shape and dtype: The output tensor has the same spatial dimensions and data type as the input — no host-side conversion is needed.

Expected Output

The output shows the image rotated 45 degrees with the content kept centred:

../../_images/tabby_tiger_cat.jpg

Original Input Image
../../_images/cat_rotate.jpg

Output: Rotated 45 degrees (centred)

CV-CUDA Operators Used

Operator

Purpose

cvcuda.rotate()

Rotate an image by an arbitrary angle with configurable interpolation

Common Utilities Used

See Also