Creating a Color Anaglyph from a Pseudo-Stereo Pair of Images Alkhadour W. University of Bradford, U.K. [email protected] Ipson S. University of Bradford, U.K. [email protected] Zraqou J. University of Bradford, U.K [email protected] Qahwaji R. University of Bradford, U.K. [email protected] Haigh J. University of Bradford, U.K. [email protected] ABSTRACT Anaglyphs provide an inexpensive method for the 3D visualization of a scene by superimposing a pair of stereo images in different color planes of single image, for subsequent viewing through colored glasses,. For example, the left image may be viewed through a red filter and the right image through a green or cyan filter. The resulting scene may appear in monochrome (yellow or grey), or in color with possibly some ghosting visible. In this paper we present a method of filtering the color of the anaglyph and controlling the amount of saturation in order to eliminate the ghosting effect while maintaining the 3D visualization. We, also describe the method we use to construct pseudo stereo pair images from two more general views, for use in an anaglyph. Key Words: Anaglyphs, Hue, Saturation, Intensity, Stereopsis, Ghosting. 1. INTRODUCTION method displays the left and right images Stereopsis is the term that refers to the alternatively and views through synchronized combination of images presented to both eyes shuttered glasses, while the third method views to achieve a 3D perception of the world the left and right images at the same time according to Steinman et al [1].Several through polarizing or colored filters. The latter technologies have been developed for 3D anaglyph technique is the simplest and least visualization including glasses independent expensive way to generate and view auto stereoscopic displays, glasses dependent stereoscopic images. An anaglyph is generated Time-Multiplexed stereo rendering and glasses by superimposing a pair of stereo images in dependent Time-Parallel stereo rendering. The different color planes of a single image which first method may use a parallax technique is then viewed through suitable colored glasses within the display to prevent one eye seeing so each eye sees only the appropriate image. the image intended for the other. The second Red and green or red and green/blue are the colors often used in the left and right sides of suggestions for future work are indicated in the glasses respectively. section 6. The 2D anaglyph is viewed as a 3D scene when the red filter blocks the blue/green components 2. Related Problems of the anaglyph image, so the left eye sees only Although anaglyphs provide an inexpensive the red image formed from the left image and means of 3D visualization, there are some in similar way the blue/green filter blocks the drawbacks related to their use. The primary red component of the anaglyph and thus the disadvantage is that, unlike the shuttered or right eye sees only the blue/green component polarizing glasses techniques, the use of a formed from the right image. This technique fixed pair of color filters does not allow the allows the visual cortex to fuse the viewed generation of arbitrary ghost free full-color 3D images so our brain interprets them as a 3D visualizations. Each pixel in an anaglyph gets impression with combined colors resulting its color from both left and right images and from the colors in the superimposed images. the result is grey for equal red/cyan The first anaglyph image was produced in combination and yellow for the equal 1853 by Wilhelm Rollmann in Leipzig and by red/green combination. It is a challenging task to accurately display the colours of the original J.C.D Almedia as mentioned in [2], but it was stereo image into a single pixel in the anaglyph patented in 1891 by Louis Ducos du Hauron. image. The problems which may cause Anaglyphs can be used in many applications degradation of the quality of the anaglyph are, including video games, theatrical films, DVDs ghosting or crosstalk, retinal rivalry or called and in science. In science the depth perception binocular rivalry, and colour merging. has many uses. It can reveal geologic features Ghosting reduces, and might sometimes by improving the visualization quality of geo- prevent the viewer perceiving depth [7]. This morphological maps [3]. It is used in NASA phenomenon occurs when the eye sees the applications such as the 2003 Mars image it is supposed to see and also a part of Exploration Rover Mission [4] and the current the other image which should be totally STEREO mission for solar investigation which blocked from the sight of this eye. This may uses two spacecraft orbiting around the Sun to result in a double image in some parts of the provide the two different views of the sun at scene. Retinal rivalry or binocular rivalry the same time [5]. In medical applications occurs when all colours are not displayed by anaglyphs are used for exploring budding viral the display device. Color merging is the particles [6], and for visualizing the heart in phenomenon which occurs when color 3D using ultra-sound. In this paper we propose components of the left and right images are a method to generate color or monochrome transferred to the same color [8]. anaglyph images from un-calibrated image pairs. This method applies filters to control the 3. Previous Work color content of the left and right components Several methods have been proposed to of the anaglyph to eliminate ghosting effects generate anaglyphs. The Photoshop method while allowing the amount of saturation to be (PS) [8] is the simplest for implementation. In adjusted in order to ensure corresponding this method for every pixel in the anaglyph features are presented to both eyes so a 3D image, the red value is the red color visualization results. In section 2, we discuss component of the left image and the blue/green problems related to generating anaglyphs, in value is the blue/green color component of the section 3 we survey the previous work, in right image. However, for example, if an section 4 we present our method and in section imaged region is red then it will only be visible 5 we show some experimental results. Some to the left eye and will not produce a 3D effect. In the modified Photoshop method (MPS), the resulting colors out of the RGB color range. same technique is followed, but the red and For this reason a clipping process is blue/green anaglyph values are the intensity performed. Although this method takes into values calculated from the left and right color account the properties of the filters, it still images respectively. This produces a grey suffers from ghosting. Analyzing the anaglyph when corresponding left and right anaglyphs that resulted from Eric Dubois image features have equal intensity. The method (Least square) shows that, this method original PS algorithm and its variant the requires the clipping process, but on the other modified PS method don’t take into account hand no ghosting was detected in the tested the transmission function of the filters, as a anaglyph image. While the Midpoint result the generated anaglyph will be the same algorithm is the best for forming anaglyph with regardless of the type of glasses we use. high quality colours and good details, it still Another linear method for generating suffers from ghosting. On the other hand, the anaglyphs was proposed by Dubios [8], who least square method produces anaglyph image took into account the fact that the color which is a bit dark with less details, and this transmission properties of the glasses in the can be solved by applying gamma correction, computation of the anaglyph. Based on a least but the advantage of this method is that, there squares approach, another method was is little ghosting. Finally, the PS method is the proposed by Zhang and Mcallister [9]. This simplest method for executing, but it suffers takes into account the spectral distribution of ghosting and poor colour quality representation the display primaries and the transmission as shown in [8]. From the previous comparison function of the filters in attempting to improve we found that none of the previous described the quality of the anaglyph. In [8] Sanders and methods can produce colour anaglyph without McAllister introduced a method to create any ghosting or region merging. anaglyph which depends on minimizing the This motivated some researchers to find distance between colour channels visible methods to solve the ghosting problem and through the glasses. In [10] a study generating generate anaglyph with better quality. In [11], colour anaglyph takes into account three the authors proposed three methods to produce functions: the transmission properties of the anaglyphs with high quality and minimize the filters, the spectral density function of the undesired ghosting artifacts. They achieved display primaries and, the color metric this by employing the following three methods, properties of the human visual system. This Stereo Pair Registration, Colour Components attempted to generate anaglyph images which Blurring, and Depth Map Manipulation and are as similar as possible to the original stereo- Artificial Stereo Pair Synthesis. In [12] the pair images. authors proposed a new method for panorama The work in [8] demonstrates some of the visualization, which is based on a colour problems which afflict the generation of anaglyph technique. This new method has the anaglyphs with high color quality. They used a advantage, of providing binocular depth cues, stereo pair of images of an Indian mother and over the classical panorama visualization her daughter of size 443 x 389 pixels, to test method which provides only monocular depth the performance of the three algorithms PS cues.