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Multi-spectral Flash Imaging under Low-light Condition using
Optimization with Weight Map
Bong-Seok Choi, Dae-Chul Kim, Wang-Jun Kyung and Yeong-Ho Ha
School of Electronics Engineering, Kyungpook National University, 1370, Sankyuk-dong, Buk-gu, Dae-gu, Korea
Keywords: Multi-spectral Flash, Weight Map, Computational Photography.
Abstract: Long exposure shot and flash lights are generally used to acquire images under low-light environments.
However, flash lights often induce color distortion, red-eye effect, and they can disturb the subject. The
other hand, long-exposure shots are prone to motion-blur due to camera shake or subject-motion. Recently,
multi-spectral flash imaging has been introduced to overcome the limitations of traditional low-light
photography. Multi-spectral flash imaging is performed by combining the invisible and visible spectrum
information. However, common multi spectral flash approaches induce color distortion due to the lower
accuracy of the invisible spectrum image. In this paper, we propose a multi-spectral flash imaging algorithm
using optimization with weight map in order to improve color accuracy and brightness of image. The UV/IR
and visible spectrum images are firstly captured, respectively. Then, to compensate luminance value under
low light condition, tone reproduction is performed by using adaptive curve due to image features that is
obtained by Naka-Rushton formula. Next, to discriminate uniform regions from detail regions, weight map
is generated by using Canny operator. Finally, the optimization object function takes into account the output
likelihood with respect to the visible light image, the sparsity of image gradients as well as the spectral
constraints for the IR-red channels and UV-blue channels. The performance of the proposed method has
been subjectively evaluated using z-score, and we also show that output images have improved color
accuracy and lower noise with respect to other methods.
1 INTRODUCTION
Cameras generally produce images by acquiring
light in a controlled fashion: camera shutter speed,
aperture, and flash all play important roles in the
acquisition process. In particular, the most common
solutions for low-light photography are either the
use of flash lights or the use of long exposure times.
On one hand, flashes often introduce undesired
artifacts or effects, such as red-eyes, false shadows,
high intensity specular reflections and changes in the
color of ambient light. Furthermore, flash lights may
dazzle the subjects because of their impulsive nature
and high intensity. A number of methods have been
proposed to reduce the artifacts produced by the use
of flash lights, for example, highlight and reflection
removal by gradient coherency (Agrawal et al.,
2005). On the other hand, long-exposures are
particularly difficult because of possible subject or
camera motion, which will produce image blur.
While blur due to subject motion is a harder
problem, blur resulting from camera shake has been
approached by various methods, such as new
imaging systems that introduce panchromatic pixels
as the image prior (Wang, 2012) or the estimation of
motion blur, e.g. by solving a maximum a-posteriori
problem (Fergus et al., 2006; Jiaya, 2007).
Research on the acquisition of high-quality
images in low-light environments is very active
topic and a number of solutions have been proposed,
the general trend being the acquisition of extended
data (multi-spectral images or multiple exposures).
One of such approach is based on flash/no-flash
image couples and bilateral filtering: image noise in
the no-flash image is reduced via bilateral filtering
and detail is transferred from the flash image using
joint-bilateral filtering (Petschnigg et al., 2004;
Eisemann et al., 2004). However, this method still
requires the use of a flash gun, which may result in
subject discomfort. Another approach requires the
acquisition of one image in the visible spectrum and
one in the UV/IR spectrum. The acquisition is
possible owing to the extended sensitivity of modern
digital camera sensors and the use of an invisible
33
Choi B., Kim D., Kyung W. and Ha Y..
Multi-spectral Flash Imaging under Low-light Condition using Optimization with Weight Map.
DOI: 10.5220/0004657500330039
In Proceedings of the 9th International Conference on Computer Vision Theory and Applications (VISAPP-2014), pages 33-39
ISBN: 978-989-758-003-1
Copyright
c
2014 SCITEPRESS (Science and Technology Publications, Lda.)