In this article, we present a review of the driving principles and parameters of a previously reported focal-plane tone-mapping operator. We then extend it in order to include color information processing. The signal processing operations required for handling color images are white balance and demosaicing. Neither white balance nor demosaicing are carried out in the focal plane, in order to avoid increasing circuit size and complexity. Since, in this case, white balance is carried out after tone mapping, multiplication of red and blue channels by constant gains may lead to wrong color results. An alternative approach is proposed, in which different gains are assigned for every red and blue pixel of the matrix. Because of the introduction of color, a modification in the original circuit is proposed, which affects the integration time of red and blue pixels. This modification leads to a reduction in the number of photodiodes required in the pixel array, and hence to a reduction of the sensing circuit area. The results produced by the operator are compared to those obtained from two other digital tonemapping operators.
This letter presents new insights into a High Dynamic Range (HDR) technique recently reported. We demonstrate that two intertwined photo-diodes per pixel can perform tone mapping under unconstrained illumination conditions with a single exposure. Experimental results attained from a prototype chip confirm the proposed theoretical framework. It opens the door to the realization of imagers providing HDR images free of artifacts without requiring any digital post-processing at all.Index Terms-high dynamic range, split-diode, automatic adaptation, single exposure, tone mapping.
Active pixel sensors are very suitable for the implementation of a large variety of image processing algorithms at the focal plane level. We propose a new focal plane image compression algorithm that is implemented with 607 transistors inside every 4 × 4 pixel block of a CMOS imager, using conventional 0.35 μm integration technology. We describe the theory of the proposed method, which is based on DPCM of the average block luminance and on VQ of four low-frequency components obtained by a linear transformation applied to the local pixels. We introduce the analog hardware of the pixel block and, to validate our design, present image coding results obtained from electrical Spice simulations of 64 pixel blocks.
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