Method to rotate a bitmap image 90 degrees

Details Method to rotate a bitmap image 90 degrees Method to rotate a bitmap image 90 degrees

1989-12-20

1992-05-05

Brier, Jeffery A.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340750, G09G 106

Patent

active

051111926

ABSTRACT:
An algorithm for rotating an image 90 degrees starts with an array or r rows and c columns of pixels. Each column of the pixel array is partitioned into words of w pixels each, and the rows, the columns, the words in each column, and the pixels in each word of the pixel array are all numbered starting at zero. Let v= r/w , where r/w is the smallest integer greater than or equal to r/w. Similarly, let h- c/w . The algorithm stores words of the original pixel array into a linear word organized memory as follows: it circular right-shifts each word i of column j by (j)mod w pixel positions and then writes in parallel this modified word into word address vj+i of the memory. The algorithm fetches words of the stored pixel array from this memory rotating this pixel array 90 degrees as follows: it reads a whole word in parallel such that each pixel p of this word comes from pixel p of word address wvi+v((p+j+1)mod w)+ wv-j-1/w) and then circular right-shifts this word by (j+1)mod w pixel positions, thereby delivering word i of column j of a 90 degree rotated version of the original pixel array.

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IEEE CG&A, The Image Prism: A Device for Rotating and Mirroring Bitmap Images, Cary Kornfeld, AT&T Bell Laboratories.

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