Browse Prior Art Database

MULTI-RESOLUTION DECOMPOSITION FOR ZOOMING BI-LEVEL IMAGES

IP.com Disclosure Number: IPCOM000007703D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-16
Document File: 3 page(s) / 264K

Publishing Venue

Motorola

Related People

Zaffer Merchant: AUTHOR

Abstract

One area of growing interest is the ability to send a printed document containing dithered (half-tone) images, such as in newspaper articles and reports, from a fax machine to a wireless device equipped with a monochrome or color LCD screen. Because the display resolution of small portable devices is expected to be much less than that used to repre- sent a fax document (1768x2288 pels) techniques for scrolling, panning and zooming will need to be employed to traverse the document. Dithered or half tone images in fax documents when zoomed start to lose their visual quality and sometimes are scarcely discernible. A method is proposed that allows zooming of images while actually improving the vis- ual quality ofthe zoomed image.

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ml MO7VROLA

V Technical Developments

MULTI-RESOLUTION DECOMPOSITION ~FOR

ZOOMING BI-LEVEL IMAGES

by Zaffer Merchant

ABSTRACT

  One area of growing interest is the ability to send a printed document containing dithered (half-tone) images, such as in newspaper articles and reports, from a fax machine to a wireless device equipped with a monochrome or color LCD screen. Because the display resolution of small portable devices is expected to be much less than that used to repre- sent a fax document (1768x2288 pels) techniques for scrolling, panning and zooming will need to be employed to traverse the document. Dithered or half tone images in fax documents when zoomed start to lose their visual quality and sometimes are scarcely discernible. A method is proposed that allows zooming of images while actually improving the vis- ual quality ofthe zoomed image.

INTRODUCTION

  Continuous-tone grey-level images are commonly used in computers and included in newspapers, arti- cles, reports and documents. In computers equipped with LCD screens it is relatively common to be able to display up to 256 shades of grey color. However, most printed media do not render the image using colors that are shades ofgrey but instead use a tech- nique called half-toning. In half-toning a grey pixel is represented using a block of pixels where the vis- ual perception of various shades of grey is achieved by different distributions of only black and white pixels (no grey) in the block; the shades of grey are achieved at the expense of increasing the resolution of the document in pixels.

  One area of growing interest is to be able to send a printed document containing half-tone black and white images, such as newspaper articles and reports, from a fax machine to a wireless device equipped with a monochrome or color LCD screen. In addition, because the display resolution of small portable devices is expected to be much less than that used to represent a fax document (1768x2288

pels), techniques for scrolling, panning and zooming will need to be employed. The simplest and most commonly used technique for zooming a dithered image is downsampling and upsampling-delete sam- ples when zooming out and re-insert the samples when zooming back in. #However, dithered or half- tone images in fax documents when zoomed start to lose their visual quality and sometimes are scarcely discernible. Instead what is proposed is a multi- resolution representation of the image using a wavelet decomposition into subbands.

  Subband coding can be viewed as a decomposi- tion of an image into an orthogonal multiresolution representation where each successive level in the decomposition results in a low-pass component which is...