Abstract: To improve the quality of low illumination image, a new image enhancement algorithm
based on HSI color space is proposed. First, we convert the RGB image into the HSI color space, and
then perform enhancement to the saturation S and brightness I respectively with different methods. To
make the image more suitable for human visual habit, piecewise exponential transformation is used
for the enhancement of the saturation component S. While the V-system, a new orthogonal
multi-wavelet, is introduced for the enhancement of the luminance component I. First, we perform
V-transform to the luminance I to isolate the high, low frequency sub-bands. And then process
Retinex adjustment to the low-frequency sub-band to reduce the influences of illumination to the
image, while we use improved fuzzy enhancement to the high frequency sub-band to achieve image
denoising and enhancement. Finally, the processed S, I and H components are synthesized into a clear
RGB image. The experiment results show that our algorithm can obviously improve the visual effect
of the low illumination color image, and also has significant improvement in the objective evaluation
indexes.

Key words: low illumination image, image enhancement, V-transform, Retinex algorithm, fuzzy
enhancement