composable_kernel/client_example/27_im2col_col2im

Client Example: im2col and col2im Transformations

Theory

This client example demonstrates im2col (image-to-column) and col2im (column-to-image) transformations. These operations are used to convert image data into a matrix form suitable for GEMM-based convolution and reconstruct images from column representations.

Mathematical Formulation:

• im2col: Rearranges image blocks into columns, mapping a 3D/4D tensor to a 2D matrix.
• col2im: Reverses the process, mapping a 2D matrix back to an image tensor.

Algorithmic Background:

• im2col is used to lower convolution to matrix multiplication (GEMM).
• col2im is used to reconstruct the original image or feature map from the column representation.
• These transformations are essential for efficient convolution implementations on GPUs.

How to Run

Prerequisites

Please follow the instructions in the main Build Guide section as a prerequisite to building and running this example.

Build and run

cd composable_kernel/client_example/27_im2col_col2im
mkdir build && cd build
cmake -DCMAKE_CXX_COMPILER=/opt/rocm/bin/hipcc ..
make -j

# Example run (image to column)
./image_to_column

# Example run (column to image)
./column_to_image

Source Code Structure

Directory Layout

client_example/27_im2col_col2im/
├── image_to_column.cpp         # im2col: image to column transformation
├── column_to_image.cpp         # col2im: column to image transformation
├── CMakeLists.txt              # Build configuration for the example

Key Functions

• main() (in each .cpp):
  Sets up input tensors, configures transformation parameters, launches the im2col or col2im kernel, and verifies the result.
• im2col/col2im kernel invocation:
  Uses the Composable Kernel device API to launch the transformation.

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Additional Details

• Supports various image and patch sizes.
• Example parameters can be adjusted in the source for different workloads.

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Related Examples

• 52_im2col_col2im: im2col/col2im in the main example directory
• 09_convnd_fwd: N-dimensional convolution using im2col

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