High-greyscale X-ray film image enhancement algorithm based on brightness gain compensation and blackbody radiation chromatography remapping

In order to solve the problem that ultra-8-bit high-greyscale X-ray film taken by a charge-coupled device (CCD) line scan camera cannot be directly visualised, an adaptive enhancement algorithm based on brightness gain compensation is proposed. Firstly, in order to solve the problem that a 12-bit image cannot be displayed, the prior eigenvalues of the image are extracted and a greyscale correction factor based on a feature prior coefficient is constructed. The greyscale distribution characteristics of the image are assessed by calculating its skewness to determine exposure levels, leading to the construction of a non-linear global mapping function for visualising 12-bit high-greyscale images. To address the significant information loss in high-greyscale images processed by existing pseudo-colour algorithms, this paper establishes a relationship between the spatial function of high greyscale and factors such as blackbody radiation, light wave wavelength, temperature and greyscale value. A red, green and blue (RGB) colour space is also designed based on brightness gain compensation to achieve pseudo-colour transformation of high-greyscale images. To verify the effectiveness of the proposed method, it is applied to various images, including a 12-bit X-ray image of an oil pipeline, a 24-bit digital radiography (DR) image of a steel pipe weld, a 14-bit infrared image and a precision casting image with defects. Quantitative experimental results indicate that the design method effectively highlights image texture details, demonstrating greater universality and adaptability for processing various types of greyscale image. Additionally, evaluation indicators reflecting human vision are improved.