Abstract
We report a low complexity, non-iterative method for enhancing the sharpness, brightness, and contrast of the pictorial content that is recorded in a digital hologram, without the need of re-generating the latter from the original object scene. In our proposed method, the hologram is first back-projected to a 2-D virtual diffraction plane (VDP) which is located at close proximity to the original object points. Next the field distribution on the VDP, which shares similar optical properties as the object scene, is enhanced. Subsequently, the processed VDP is expanded into a full hologram. We demonstrate two types of enhancement: a modified histogram equalization to improve the brightness and contrast, and localized high-boost-filtering (LHBF) to increase the sharpness. Experiment results have demonstrated that our proposed method is capable of enhancing a 2048x2048 hologram at a rate of around 100 frames per second. To the best of our knowledge, this is the first time real-time image enhancement is considered in the context of digital holography.
Highlights
In a digital hologram, a complex on-axis hologram H x, y records the object waves that are emitted from the object points in a three dimensional (3-D) scene
This is caused by the distortion on the entire hologram as the intensity of each pixel is modified after the histogram equalization process
We report a method based on the concept of virtual diffraction plane (VDP) to enhance the optical properties of pictorial contents that are recorded in a hologram
Summary
A complex on-axis hologram H x, y records the object waves that are emitted from the object points in a three dimensional (3-D) scene. It is sometimes difficult to control the illumination in the capturing process, or the nature of the image scene to attain the desired optical properties (such as sharpness, brightness and contrast), resulting in blurriness, over or underexposure in the reconstructed image In traditional photography, this kind of defects can be compensated by re-adjusting the intensity of individual pixels. Local modification on the VDP will invoke, to a good approximation, similar changes on the optical properties of the object scene it represents On this basis, we apply a variant of the classical histogram equalization method [7] to the VDP image to flatten the probability distribution of the pixel intensity, leading to improvement in its brightness and contrast. The VDP is diffracted back to the original plane of the digital hologram to become a processed digital hologram
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