In this paper, we present a simple yet effective method that takes advantage of the gradient information to accomplish the multiexposure image composition in both static and dynamic scenes. Given multiple images with different exposures, the proposed approach is capable of producing a pleasant tone-mapped-like high-dynamic-range image by compositing them seamlessly with the guidance of gradient-based quality assessment. In particular, two novel quality measures, namely, visibility and consistency, are developed based on the observations of gradient changes among different exposures. Experiments in various static and dynamic scenes are conducted to demonstrate the effectiveness of the proposed method.

The paper shows how to convert the order-8 cosine transforms into a family of integer cosine transforms (ICTs) using the theory of dyadic symmetry. The new transforms can be implemented using simple integer arithmetic. It was found that performance close to that of the DCT can be achieved with an ICT that requires only 4 bits for representation of its kernel component magnitude. Better performance can be achieved by some ICTs whose kernel components require longer bit lengths for representation. ICTs that require 3 bits or less for representation of their component magnitude are available but with degraded performance. The availability of many ICTs provides an engineer the freedom to tradeoff performance for simple implementation in designing a transform codec. IntroductionTransform coding can achieve a high data compression rate for image data. A transform coder comprises mainly two parts : the first part transforms highly correlated image data into weakly correlated coefficients using an orthogonal transform and the second part performs adaptive quantisation on coefficients to reduce the bit transmission rate. It has been widely accepted that among the many suboptimal orthogonal transforms the discrete cosine transform (DCT) has the best performance in both data compression and filtering for image data [I, 21. The DCT has also been shown to be asymptotically optimal for a first-order Markov source [3, 41, which is regarded as a good stochastic representation of image data. As block sizes of 8 and 16 are most appropriate for the transform coding of image data, therefore techniques for implementing order-8 and -16 DCTs economically and with fast computational time are very important for the realisation of a transform codec. The DCT can be implemented using either a programmable processor or dedicated hardware. For an order-n DCT, the magnitudes of the components of the 0th and (n/2)th basis vectors can be reduced to unity by suitably scaling components of these basis vectors. However, components of other basis vectors are irrational numbers which cannot be reduced to integers by simple scaling. Being real numbers, the components cause diffiPaper 67911 (E16), first received 24th October 1988 and in revised form 9th December 1988 The author is with the Department of Electronics, the Chinese University of Hong Kong, Shatin, N.T., Kong Kong 276 culties in both implementation methods. Dedicated hardware that computes the DCT using floating point arithmetic is very complex and expensive. On the other hand, a programmable processor which computes the DCT by executing a sequence of instructions does not usually have instructions that handle real numbers. Although floating point co-processors which have been specially tailored for processing floating point arithmetic can be found on the commercial market, they are also very expensive.A simple method to eliminate floating point arithmetic is to approximate the real magnitudes of the DCT components by M-bit integers, so that the DCT can be computed using integer ...

In this paper, we present a simple yet effective method that takes advantage of the gradient information to accomplish the multi-exposure image composition in both static and dynamic scenes. Given multiple images with different exposures, the proposed approach is capable of producing a pleasant tonemapped-like high dynamic range (HDR) image by compositing them seamlessly with the guidance of gradient-based quality assessment. Especially, two novel quality measures: visibility and consistency, are developed based on the observations of gradient changes among different exposures. Experiments in various static and dynamic scenes are conducted to demonstrate the effectiveness of the proposed method.

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