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Abstract
Many image display applications and printing device s allow only limited number of colours. They have limited computational power and storage to produce high quality outputs on high bit-depth colour image . A dithering technique is called for here in order to improve the perceptual visual quality of the limite d bitdepth images. A dithered image is represented by a natural colour in the low bit depth image colour fo r displaying and printing. This technique obtains low cost colour image in displaying the colour and pri nting image pixels. This study proposes the dithering tec hnique based on Tchebichef Moment Transform (TMT) to produce high quality image at low-bit colour. Ea rlier, a 2 ×2 Discrete Wavelet Transform (DWT) has been proposed for better image quality on dithering . The 2 ×2 TMT has been chosen here since it performs better than the 2 ×2 DWT. TMT provides a compact support on 2 ×2 blocks. The result shows that 2 ×2 TMT gives perceptually better quality on colour image d ithering in significantly efficient fashion.
Highlights
Most colour image printing and displaying devices have limited capability of reproducing dot points
This study proposes the dithering technique based on Tchebichef Moment Transform (TMT) to produce high quality image at low-bit colour
The average error score of colour image dithering based on Floyd Steinberg, 2×2 Discrete Wavelet Transform (DWT) and 2×2 TMT for 40 natural images and 40 graphical images of size 512×512 pixels are shown in Table 3 and 4
Summary
Most colour image printing and displaying devices have limited capability of reproducing dot points. An image dithering approach can display the colour image in limited number of bits where the specific colour at each pixel are defined in colour tables or colour palette. Digital dithering is a process of generating a pattern of dot with limited colour numbers to reproduce a visually appealing result (Yao and Wan, 2010). It diffuses the quantization error in a local area of an image to its neighbouring area. In order to overcome the complexity of DWT, this study proposes Tchebichef moments for efficiency and simplicity to dither colour image. Experimental results show that TMT requires lower computation to dither colour image than DWT. The DWT of function f(x,y) of size 2×2 is given in (7) and (8) as follows Equation 7 and 8:
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