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Realtime Aspect Ratio Conversion for PC Graphics Emulation

IP.com Disclosure Number: IPCOM000062440D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Blackard, JW: AUTHOR [+3]

Abstract

By modifying the bit map of a PC color graphics image, it is possible to map the color graphics image to a monochrome display of higher resolution and maintain the proportionate shapes of geometric objects in the image. A PC color graphics image is 640 X 200 pels (picture elements) with a pel aspect ratio of approximately 2.1:1. The high resolution monochrome display which was used for the emulation is an all-points- addressable (APA) display with a square pel ratio and a 720 X 512 pel image. The problem is to modify the color graphics image and map it to the high resolution monochrome display with an aspect ratio of 1:1 so that geometric objects, such as circles, produced on the lower resolution display will maintain their proportionate shape when transferred to the high resolution screen.

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Realtime Aspect Ratio Conversion for PC Graphics Emulation

By modifying the bit map of a PC color graphics image, it is possible to map the color graphics image to a monochrome display of higher resolution and maintain the proportionate shapes of geometric objects in the image. A PC color graphics image is 640 X 200 pels (picture elements) with a pel aspect ratio of approximately 2.1:1. The high resolution monochrome display which was used for the emulation is an all-points- addressable (APA) display with a square pel ratio and a 720 X 512 pel image. The problem is to modify the color graphics image and map it to the high resolution monochrome display with an aspect ratio of 1:1 so that geometric objects, such as circles, produced on the lower resolution display will maintain their proportionate shape when transferred to the high resolution screen. This problem is solved by changing the aspect ratio of the image to the square 1:1 ratio characteristic of the high resolution monochrome display. Since the color graphics image was produced for a display with a 2.1:1 aspect ratio, the correction is made by duplicating each horizontal scan row of pels. The result is a square aspect ratio of 2:2, as required. The new image has a 640 by 400 resolution which is then centered on the 720 by 512 monochrome display screen. The advantage of this approach is that, while not correcting the aspect ratio perfectly, it provides a fast and simple way for remapping the image onto a h...