Browse Prior Art Database

Extracting Data From Bitmap in Display

IP.com Disclosure Number: IPCOM000099662D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Butler, ND: AUTHOR [+4]

Abstract

In graphics displays, data to be operated on by a graphics engine may be stored in a packed pixel bitmap. This disclosure is concerned with extracting data from a single plane of a pixel bitmap into another pixel bitmap. The technique described enables only selected bits within a pixel to be updated by reconfiguration of the bitmap in memory.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 67% of the total text.

Extracting Data From Bitmap in Display

       In graphics displays, data to be operated on by a
graphics engine may be stored in a packed pixel bitmap.  This
disclosure is concerned with extracting data from a single plane of a
pixel bitmap into another pixel bitmap.  The technique described
enables only selected bits within a pixel to be updated by
reconfiguration of the bitmap in memory.

      Any area of contiguous memory can be thought of as a bitmap.
Within a bitmap a pixel may be represented by 1, 2, 4, 8, etc. bits.
For example, in the 4 bit per pixel case each byte in memory
represents two adjacent pixels in the bitmap, hence 'packed pixel'.
The graphics engine can then operate on the memory according to the
current number of bits per pixel.

      One of the common restrictions of such hardware is that it can
only access whole pixels.  Often, however, an application needs to be
able to update only selected bits within a pixel.  This is because
one bit of a pixel may represent, for example, the red content of the
pixel when it is displayed.  If an application wishes to modify the
red content of an image it will need to extract the relevant bit from
every pixel in the bitmap.  This disclosure describes a method of
extracting the required information using the capabilities of packed
pixel hardware.

      Consider a bitmap in memory which is n pixels wide and 1 deep
and where there are 8 bits per pixel, as shown in Fig. 1.  From this
bitmap we...