Color Transfer Brush Qing Luan1,2 Fang Wen2 1. University of Science and Technology of China

Problem

Ying-Qing Xu2 2. Microsoft Research Asia

Overview

Global color transfer * : not effective when images have complex composition

Regional color transfer

Source image

Target image

Result of Reinhard et.al *

Local color transfer: effectively transfer the color in each local region pair

Optimization

User-specified target regions

User-specified source regions

Transferred result

Transfer region pair **

Algorithm

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Regional color transfer The regional color transfer is done by applying the algorithm by Reinhard et.al* to each user-specified transfer region pair. That is, for the pixel with color Ct , the transferred color g (Ct ) is computed by: s

g (Ct )   s 

Challenges: 1. How to set up transfer region pairs 2. How to eliminate the discontinuity caused by local color editing We propose an interactive Color Transfer Brush for users to set up the transfer region pairs, and develop an optimization step to eliminate the discontinuity.

Where

t

(Ct  t )

 s /  t and  s /  t are the mean and variance values for source / target region

Optimization The optimization preserves the gradient of the remaining region based on the known boundary of the transferred regions, in order to eliminate the discontinuity caused by separated regional color transfer.

Result Where f is the function to optimize, g is the original image value, p q are neighbor pixels, and  is the remaining region outside the transferred regions.

Transfer region pairs***

Our result

Result of Reinhard et.al*

* Reference: E. Reinhard, M. Ashikhmin, B. Gooch, and P. Shirley. Color transfer between images. In IEEE Computer Graphics and Applications, volume 21, pages 34–41, 2001. ** In all the examples in this poster, regions of the same ‘transfer region pair’ are shown in the same color . *** The yellow brush in the examples is the ‘color maintain brush’ which tend to keep the color of the original image. For details please refer to our paper