Overview of Image-Based Shading Techniques

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26th Mar 2018 Computer Science Reference this

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  • Rishabh chand sharma
  • Brahmdutt bhora

 

Abstract Image processing input, such as a photo or video frame is an image for which any form of signal processing functions by using images using mathematical is processing. Most image processing techniques, such as a two-dimensional or three-dimensional image signal is treated. Image processing methods used are two types of analog and digital image processing. Shading is also useful in image rendering. Rendering through computer programs, (collectively, can be called a scene file or model) is the process of creating an image of the 3D model from 2D images. In the processing of images, shading is very important method for smooth the surface and get the results. Shading 3D models with varying levels of darkness in the picture refers to the depiction of depth perception. In this paper we introduce the comparisons between different types of shadings. Here introduce which shading method is best rather than others.

Keywords— image processing, image rendering, shading.

I. INTRODUCTION

An image is an array, or matrix, of square pixels (picture elements) arranged in rows and columns. A grayscale image (8 bit) for each picture element ranges from 0 to 255 that is a fixed intensity. Each picture element of grayscale images (8 bit) usually calls a black and white image, but the image includes many shades of gray.

Here shows square grayscale image which have different type of shade with differ values means each pixel have a particular value within range (0 to 255).

Figure 1: Each pixel has a value from 0 (black) to 255 (white). The possible range of the pixel values depend on the colour depth of the image, here 8 bit = 256 tones or grayscales.

Image processing: An image processing system is to get a magnified image (digital image) from an image or to extract some useful information from it. This is a method to take some action on it. The characteristics associated with the input image or the image can be output as video frames or photo, is a type of image in which the signal system. They have already set up to implement signal processing methods, image processing systems, while generally treated as two-dimensional signals, images.

Image processing basically includes the following three steps-

  • Image importing with the optical scanner or digital photography.
  • Analysis and data compression and image enhancement which include manipulating the image and satellite images that is not like the human eye for spotting pattern.
  • The production is based on the result image or image analysis in the report can be changed, which is in the final stage.

Image processing methods used are two types of analog and digital image processing. Analog or printout of image processing and visualization techniques like photographs can be used for hard copies. Digital processing technology is using computer manipulation of digital images that helps.

The method by which images are produced – the real space, light, and the interactions between objects in the camera – often significant shading across the image field of view leads to situations where exhibits. In some cases, may be bright in the center of the image and the same goes to the edge of the field of view as the decrease in brightness. In other cases, the image on the right side to the left may be darker and lighter. Cinematography non-uniform illumination, non-uniform sensitivity camera, or on the glass can also be caused by dirt and dust (lens) surfaces.

Shading: Shading 3D models with varying levels of darkness in the picture refers to the depiction of depth perception. Shading is use in the MIP and LMIP [1]. Here we include two types of shading techniques.

  • Flat shading
  • Smooth shading

Further we discuss in part II about image rendering and modeling, in part III discuss about shading techniques used in image rendering and conclude the paper in part IV.

II. IMAGE BASED MODELING AND RENDERING

Image-based modeling and rendering techniques, image synthesis recently a powerful alternative to traditional geometry-based technology has received as much attention [2].

Rendering is the process of generating an image from a model by means of a software program. The model is a description of three dimensional objects in a strictly defined data structure. It contains geometry, viewpoint, texture and lighting information [3].

We can distinguish two fundamental approaches to rendering: geometry-based and image-based rendering.

  • In geometry-based rendering, a scene is described using geometrical primitives, which are discredited into points, lines and triangles for rendering [3].
  • In image-based rendering, a scene is rendered making use of multiple input images, without any 3D object or scene information [3].

Most rendering algorithms are a combination of these two paradigms, for example texture mapping (image-based) in polygon rendering (geometry-based) [3].

In the image rendering we use three types of rendering techniques.

  • Scanline rendering: Scanline rendering instead of a line-by-line on the works that appear as 3D computer graphics, is an algorithm to determine the surface of a polygon-to-polygon or pixel by pixel.

All of polygons before they appear for the first time at which the Y, the image on the front of each line or polygon with scanline sorted list by using the intersection of a scanline calculations, are solved by coordinating the provided that the sorted list is not as advanced active scaline photo below, visible long polygon is updated to discard.

The main advantage of this method is that the scanning plane with the usual sorting corner reduces the number of comparisons between the edges.

  • Ray tracing: Ray tracing through pixels in an image plane of light tracing the path of light through pixels and their encounters with virtual objects to create an image by simulating the effect of a technique.
  • Ray casting: Ray casting computer graphics and computational geometry to solve a variety of problems in testing is the use of ray-surface intersection.

2D image based rendering: Such sprites, billboards, Impostors, and Layering image on a screen to display images as 2D techniques. Sprites, billboards, and Impostors some demarcation geometry as a structure instead of applying the image, image technique employs an off-screen.

3D image based rendering: 3D IBR 2-D methods when compared to the realism of rendered images, but only slightly increased with the complexity that involves the addition of several techniques. Examples of IBR layered 3D depth, images, view morphing, and includes view interpolation.

4D image based rendering: Last IBR approach to provide a four-dimensional function, a simplified view function Plenoptic implements. Image data for synthetic and real-world scenes recently developed two methods for rendering camera views have been.

Figure 2: A variety of rendering techniques applied to a single 3D scene

III. IMAGE BASED SHADING AND TECHNIQUES

Color presents a problem for shape-from-shading methods because it affects the apparent “shading” and hence the apparent shape as well [4].

We take as our definition of shading that it is the sum of all the processes affecting the image intensity other than changes in surface color (hue or brightness). Shading arises from changes in surface orientation and illumination intensity [4]. Shading 3D models with varying levels of darkness in the picture refers to the depiction of depth perception.

Shading less dense or lighter areas with a lighter shade or darker areas more densely media apply a darker shade on the paper with dark levels is used for illustration in the drawing, and is . The straight lines of varying proximity to the shadows are drawn in a grid pattern in a region where there are different techniques of cinematography, including the cross hatching. Dark, with the lines and odd field appears. Similarly, the different lines, appears lighter area.

Figure 3: Example of shading

In the image processing, we shaded the image with the help of two techniques-

  • Flat shading
  • Smooth shading

Flat shading: Their respective colors and a lighting technology is used in each polygon of an object based on the angle between the intensity of the light source 3D computer graphics and general surface light source in the direction of flat polygon shading shadow.

The main disadvantage of the flat shading, the low polygon model provides a versatile look. Sometimes may be it boxy look modeling objects such as profit through.

Smooth shading: The main disadvantage of the flat shading, the low polygon model provides a versatile look. Sometimes it boxy look modeling objects such smooth shading, pixel by pixel, to the contrary, flat shading with color changes. The curved surfaces of the polygon vertices interpolation technique uses to calculate the values ​​of the pixels holds. Smooth shading Hakrup divided into two major categories through the benefits might be.

  1. Gouroud shading: Gouraud shading surfaces represented by polygon meshes to produce continuous shading of computer graphics is used as an interpolation method.

Gouraud shading is most often at the corners of each triangle of light and linear triangle covered by computing the resulting color for each pixel by interpolating surfaces triangle is used to obtain continuous light. Gouraud shading, flat shading and Phong shading is considered better than the much less processing is required, but generally results in a multilateral track.

Phong shading than, Gouraud shading strength and weakness lies in its projection. The corner count expensive light color values ​​from samples interpolating, corner than a mesh screen space covers more pixels, so as to reduce the processor Phong shading calculations performed for each pixel of light is intense. However, the highly localized light effects will not be rendered correctly, and in the middle of a polygon is a highlight, but does not spread to the top of the polygon, then it will not be clear in rendering a Gouraud; A highlight is on top of a polygon Conversely, if, it will be rendered correctly on the summit, but all through the neighboring polygon interpolation method will be spread across unnatural.

Figure 4: Comparisions of Flat shading and Gouroud shading

 

  1. Phong shading: Phong shading 3D computer graphics shading the surface as an interpolation technique shows. It also called Fong interpolation or normal vector interpolation shading. In particular, the rasterized polygon normals across the surface of the interpolated normals and interpolates and calculates a reflection model based on pixel color. Interpolation and Fong Fong Fong shading also can refer to specific combinations of reflection model.

Gouraud shading Phong shading correction and the shading of a smooth surface provides a better approximation. Phong shading a smooth surface normal vector is different. Phong reflection model, such as the small specular highlights that when applied to a reflection model Fong interpolation method works better than Gouraud shading.

Figure 5:Visual illustration of the Phong equation: here the light is white, the ambient and diffuse colors are both blue, and the specular color is white, reflecting a small part of the light hitting the surface, but only in very narrow highlights. The intensity of the diffuse component varies with the direction of the surface, and the ambient component is uniform (independent of direction).

Specular highlights are found in the middle of a large polygon Gouraud shading with the most serious problem occurs. The specular highlights peak based on the color of the polygon vertices and Gouraud shading interpolates are absent, specular highlighting will disappear from the interior of the polygon. This problem is fixed by Phong shading.

 

Figure 6: Comparisions between flat shading and phong

Shading

Figure 7: Comparisions between flat, gouroud and phong shading

IV. CONCLUSION

Image processing is the wide area use in everywhere like in medical, video games, visual effects etc. Rendering is the method for view digital images and process them. Shading is use in image rendering. In this paper we represent the shading techniques and show the comparisons between them. Now conclusion of this paper is, Phong shading is better than other shading techniques like as flat shading and gouroud shading. In the further technologies we discuss the upcoming shading techniques.

 

V. ACKNOWLEDGEMENT

The first guide is thankful to Brahdutt Bohra for instructive suggestions, and also wants to thank the Dr. Surender yadav. The blessing, help and guidance given by him time to time shall carry me a long way in the journey of life.

REFERENCES

[1] Feng Ling, Ling Yang. “Improved on Maximum intensity projection”. 2009 International Conference on Artificial Intelligence and Computational Intelligence .978-0-7695-3816-7/09 $26.00 © 2009 IEEE DOI 10.1109/AICI.2009.202.

[2] Heung-Yeung Shum and Sing Bing Kang. “A Review of Image-based Rendering Techniques”.

[3] Mandakini Kaushik, Kapil Kumar Nagwanshi, Dr. Lokesh Kumar Sharma. “A Overview of Point-based Rendering Techniques”. International Journal of Computer Trends and Technology- volume3Issue1- 2012. ISSN: 2231-2803.

[4]Brian V. Funt, Mark S. Drew, and Michael Brockington. “Recovering Shading from Color Images”. ECCV’92, Second European Conference on Computer Vision, pp. 124-132, May, 1992.

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