Beyond Pixels: Quantum-Inspired Edge Detection for Superior Imaging

Suman Kumar Roy
5 min readAug 21, 2023

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The fusion of quantum mechanics and image analysis has given rise to a groundbreaking concept: Quantum Edge Detection. This approach marries the precision of quantum computing with the task of identifying image boundaries. By leveraging quantum properties like superposition and entanglement, Quantum Edge Detection has the potential to revolutionize accuracy and efficiency in comparison to classical methods. This exploration will delve into the core principles, challenges, and applications of this fusion, offering insights into its transformative power for image analysis and comprehension. Welcome to the world where quantum physics and digital imagery converge to redefine how we perceive and process visual data.

Edge detection is a crucial step in image feature extraction. It is widely used in classical image processing algorithms to extract the structure of objects in an image. However, classical edge detection algorithms become slow for larger images due to the huge resolution and pixel-wise computation required. Quantum Image processing, on the other hand, offers exponential speedup in certain cases and is an emerging field that is very intriguing. Quantum Image Representations (QImRs) like FRQI and NEQR can be used to convert classical images to quantum images. This section discusses the QPIE representation and the use of QImRs to perform edge detection using the QHED algorithm.

Quantum Probability Image Encoding (QPIE)

QPIE utilizes the probability amplitudes of a quantum state to encode Black-and-White or RGB images. With n-qubits available, up to 2ⁿ -states can be held in superposition. By leveraging this feature, QPIE provides an efficient and robust encoding method that significantly reduces the memory needed to store image data. For instance, only 2-qubits are required for a 4-pixel image, while a 3-qubit system is needed for an 8-pixel image. In general, the number of qubits n required for an N-pixel image is calculated as log₂N.

Classical image to QPIE state

The given example image is made up of four pixels arranged in a 2D matrix. Each pixel is represented by a binary index and has a corresponding intensity value.

This equation represents an image with two dimensions and N₁xN₂ pixels. The intensity of the pixel at position (x,y) in the image is represented by Iyx. The coordinate axes start from the top-left corner of the image.

These intensity values can be normalized to represent the probability amplitudes of a quantum state. This is achieved by dividing each intensity value by the square root of the sum of the squares of all intensity values.

Normalization

Once normalized, the quantum state of the image can be written by assigning each pixel’s normalized color value to its respective quantum state.

Quantum Represenation

Quantum Hadamard Edge Detection (QHED)

Classical edge detection algorithms are time-consuming, requiring processing of each pixel, while quantum algorithms offer exponential speedup. However, current quantum methods are inefficient due to operations and requirements for calculation. The Quantum Hadamard Edge Detection algorithm is a more efficient solution to this problem.

Application of Hadamard Gate

The Hadamard gate (H) has the following operation on the state of qubit.

The QHED algorithm uses the H-gate to detect edges in an image by manipulating binary bit-strings of adjacent pixels. Applying the H-gate to the LSB of a quantum register produces a unitary representation.

QHED without Auxilary

Time and Space Complexity analysis of QHED

We talked about the time complexity of classical edge detection algorithms, which can take O(2ⁿ) or O(mn .log(mn)). Quantum edge detection using the QSobel algorithm is faster at $O(n²), but requires a complex state preparation and more qubits. The QHED algorithm uses a more space-efficient image encoding scheme (QPIE), which reduces the number of qubits needed exponentially. The time complexity of QHED’s state preparation is slightly higher than QSobel’s, but the edge detection procedure has a time complexity of O(1), which is faster than QSobel’s O(n²).

Code

For our case, we have been implemented the quantum edge detection using auxiliary qubit and also used it on a bigger image.

In summary, Quantum Edge Detection emerges as a transformative approach at the intersection of quantum mechanics and image analysis. It offers unprecedented precision and speed by leveraging quantum principles, promising breakthroughs in fields like medical imaging, autonomous systems, and AI. While challenges exist, such as mastering quantum complexity and algorithm design, the potential rewards are immense. This innovative fusion opens new avenues for image understanding, where pixels and quantum particles unite to reshape industries and push the boundaries of visual comprehension. As quantum technologies advance, Quantum Edge Detection’s impact is poised to expand, unveiling a future where images reveal deeper insights than ever before.

References:

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Suman Kumar Roy

Completed M. Tech at NITK, Surathkal, Quantum Researcher @TCS Research, Quantum Computing, QML and Algorithm Enthusiast