Non-photorealistic rendering is a technique which is committed to generate art style works. The goal of this technique is not only to represent the authenticity of graphics but also to simulate their art features

as well as their defects. This concept was first proposed in the 1980s. After years of development

non-photorealistic rendering techniques can simulate a numerous painting styles

including oil paintings

watercolor paintings

Chinese ink paintings

pencil sketches

and cartoons. The sketch is a kind of painting which presents the light and shade of an object by lines. The color sketch is a sketch painted by a small number of color pencils. Except for the light and shade

the color sketch represents color features of an object as well. When painting a color sketch

people follow the monochrome sketch and render different regions with disparate color pencils. People usually need to blend two or more colors to obtain the desired color because the types of pencils are limited. In addition

the color mixing of sketches differs from that of oil or watercolor paintings. Typically

people mix pigments on a palette. However

when doing a color sketch

they directly draw disparate color layers on the paper. The layers of stroke for each color are superimposed and interspersed to build the target color through optical blending. This feature creates a very special kind of texture and color style for the color sketch. Although many people are fond of sketches

mastering the skill of pencil drawing is not easy for everybody. Based on previous works and characteristics of color sketch

combining the duotone color reproduction with LIC techniques

we realized an improved way of generating color sketch. First

we fulfilled a monochrome sketch simulation process based on LIC(line integral convolution). On this basis

we realized a new approach for the color sketch generation based on color customization

which can automatically convert a digital image into a colored pencil drawing

by researching on the features of the color sketch and combining with the duotones color reproduction technique. The first step of this method is image segmentation. We use a primary color

as well as a secondary color

to paint each segmented region. Our method can automatically calculate the color set of each particular region. Such kind of color customization can successfully simulate the color mixing of sketch paintings

and it can also be expanded to the simulation of similar painting styles

such as chalk drawing and pastel drawing. In addition

we propose a way to superpose the real paper texture into digital images

which will make the final effect closer to real paintings. We achieve an ideal way to generate improved profile for the color sketch based on neon-transformation because the profile is one of the most important elements. We zoom the color of the original image before generating the white noise

which generates a clear hierarchy for the final effects

to improve the contrast ratio. We also fulfill a new way for image segmentation based on K-means cluster

which obtains suitable segmentation results for the color sketch generation. To validate the effectiveness of the proposed approach

we conducted extensive experiments. Experimental results demonstrate that our approach outperforms several state-of-the-art approaches on challenging automatic and real-time transformation from color image to color painting

as well as bridging the gap between them. In contrast to Yamamoto's method

the proposed technique incorporates the idea of hierarchical method and color scale transformation into linear integral convolution with two-tone color sketch mapping technology. As such

we obtain sketch texture closer to a hand-painted effect. Matsui's method can generate a soft texture. However

the entire stroke fusion process is really complicated and time-consuming. Particularly

this method does not consider the sketch contours and could be error-prone to lose structure characteristics of the object in drawing effect. Kim's method extracts basic image feature for sketch generation. This method also has high efficiency and can be well applied to mobile devices. However

this method only considers the contour perspective

thus ignoring the sketch texture effect which often suffers a decrease in accuracy compared to real color sketch. In the comparison of the two approaches

the proposed method considers contour and texture. Simulating color image from the contour and texture aspects helps in issuing object characteristics preservation and preventing potential unrealistic sketch transformation. Way's method can generate a soft and saturated but cluttering texture

thus missing the natural line sense of color sketch. We calculate texture direction by transforming image space to frequency domain for energy statistical characteristics to tackle this issue. The simulation results obtain obvious intensive line sense. In the color fusion aspect

Way's method is based on the color of the original image and only overlays strokes texture on the basic color. However

in the real drawing process

people can only use limited colors. We have established the library of basic colors to dispose this challenge. All colors used for sketch simulation are fused from the library and by two basic color layers. Simulation results show robustness to changing imaging conditions

as well as satisfactory human visual sense. In general

our study reveals new insights into the drawing scheme

implementing method

algorithm complexity

and interactivity when simulating color sketch. First

the proposed method is accomplished using the image transformation approach. Therefore

the method can interactively transform color image to color sketch or any other basic color specified by the user. Second

our study encompasses contour and texture simulation

facilitating the simulation of a realistic painting process. Third

the proposed method finds inspiration from human drawing experience. We overlay and fuse different color layers to generate color texture. This way can also be employed to simulate a wide spectrum of painting style

such as chalk drawing and crayon drawing.