Multispectral imaging has been applied to many fields, from biological tissue characterization to environmental monitoring [
1‐
3], which has a wide range of applications. In the new medical testing, with the trend of younger and high incidence of breast tumors [
4], scholars have begun to explore a simpler, lower cost screening method for breast tissue lesions. Hyperspectral mammography [
5] may provide a means for early self-examination of breast tumors, but the strong scattering characteristics of the tissue result in low signal-to-noise ratio (SNR) and insufficient clarity of the tissue image, which prevents the accurate detection of heterogeneity [
5] (lesion tissue in the breast that is distinct from normal breast tissue). In general, the study of low-resolution problems in multispectral transmission images can be divided into two aspects: the acquisition end and the preprocessing end. On the acquisition side, Jian et al. [
6] designed an adaptive multispectral imaging system to correct the wavefront error of the illumination light for obtaining a high-resolution image of the biological tissue. Rousset et al. [
7] demonstrated an adaptive multispectral acquisition scheme based on time resolution of single-pixel imaging, which provides low-cost, high-quality multispectral images. Yang et al. [
8] optimized illumination methods using shape function signals to increase the dynamic range of multispectral imaging systems based on light-emitting diodes (LEDs), thereby improving the grayscale resolution of multispectral images. Li et al. [
9] proposed and demonstrated that multi-wavelength “synergy effects” in light-emitting diode (LED)-multispectral images obtained by frequency division modulation can be used to improve the image quality of each waveband. In hyperspectral transmission imaging, the frame accumulation technique that has been successfully applied to various low-light-level image detection devices is one of the most effective methods for enhancing weak transmission image signals. On the preprocessing side, the main methods are wavelet transform filtering, space-time domain combined filtering, and other classical image denoising methods [
10‐
13] for the low SNR and low contrast of images. However, the filtering methods may smooth the image and lose edge details. Gang et al. [
14] greatly enhanced the SNR of the low-light-level transmission image by combining the frame accumulation and the shaping signal technology, and improved the detection sensitivity of the transmission image. Starting from the preprocessing side, this paper innovatively added image synthesis and edge enhancement algorithm based on the frame accumulation of single-channel images, which obtained a method that better matched with the heterogeneity detection of the transmitted tissue image and greatly improved the image quality.
Aiming at the characteristics of tissue images, this paper designed a simulation experiment to collected multispectral phantom [
5] images to get the joint preprocessing algorithm for multispectral transmission tissue images. The experiment used liquid and solid as the phantom of breast tissue and heterogeneous tissue, respectively. The polymethyl methacrylate (PMMA) [
15] container with a transmittance up to 96% is used to hold liquid imitation for the first time. We combined the frame-accumulated averaging with the edge enhancement and image synthesis to get the joint preprocessing algorithm, which matched better with heterogeneity detection. Finally, the collected multispectral transmission phantom images are processed by this algorithm to obtained high-quality images. The experiment result shows that the peak signal-to-noise ratio (PSNR) of the image that is processed by the joint preprocessing algorithm is increased to 57.3 dB, and the image SNR is improved by 2.60 dB, which is improved by 1.11 dB compared with the filtering alone. The signal-to-noise ratio and the contrast at the edges are significantly improved. The standard deviation of the image processed by the algorithm is 19.8998 higher than the original image. And this preprocessing algorithm has been indirectly verified in our previous work [
16]: we used faster regions with convolutional neural networks features (Faster R-CNN) [
17] object detection [
18] algorithm based on deep learning to detect the image processed by the preprocessing algorithm, and reached 99.9% mean average precision (mAP) [
19]. Moreover, the detection accuracy of the transmission image processed by the algorithm is higher than that without the algorithm. Therefore, we propose a preprocessing algorithm suitable for heterogeneity detection of transmission breast tissue image based on the frame accumulation technique. The algorithm plays a good role in locating the edges of heterogeneous tissues, so it may improve the heterogeneity detection accuracy of multispectral and hyperspectral transmission tissue images to some extent.