Showing papers on "Quantization (image processing) published in 1974"

Seismic data compression methods

Abstract: This paper discusses two ways of compressing seismic data prior to long‐distance transmission for display. A Walsh transform technique and an analogous time‐domain method eliminate redundant seismic information allowing data sets to be compressed with little visual degradation. The basic approach consists of using an average 3-bit code to describe data in such a way as to minimize information loss; the method also uses the Walsh transform to achieve further compaction through sequency bandlimiting. A second technique is entirely a time‐domain operation and does not use transforms. The Walsh method, however, produces larger compression ratios than the time technique before serious image degradation occurs. Both schemes have six basic parts: bandlimiting, quantization, encoding, decoding, interpolation, and band‐pass filtering; they differ only in band limiting and interpolation. Band limiting sequencies in the Walsh domain is very similar to, but not the same as, alias filtering and resampling in time. Red...

Colour image coding using linear transformation and block quantization

Abstract: A bandwidth compression and redundancy r e d u c t i o n scheme was i n v e s t i g a t e d i n a d i g i t a l c o lour image t r a n s m i s s i o n system employing a l i n e a r t r a n s f o r m a t i o n and b l o c k q u a n t i z a t i o n technique. Colour images were represented by the N.T.S.C.'s Red, Green, Blue and Y, I , Q Rec e i v e r Primary and Transmission Co-ordinate systems r e s p e c t i v e l y . The Y, I and Q s i g n a l s were assumed to c o n s t i t u t e a homogeneous GaussMarkov random f i e l d modelled by an exponential c o r r e l a t i o n f u n c t i o n of the form R(x,x',y,y') = exp[-a|x-x'| $|y-y'|], where a, 8 a r e the c o r r e l a t i o n c o e f f i c i e n t s i n the h o r i z o n t a l and v e r t i c a l d i r e c t i o n s , r e s p e c t i v e l y . L i n e a r transformations employed were the d i s c r e t e F o u r i e r and Hadamard tr a n s f o r m a t i o n s . In the b l o c k coding scheme, b l o c k s i z e s of 8 x 8 and 16 x 16 p i c t u r e elements were used and i n the q u a n t i z a t i o n s t r a t e g y , both optimum uniform and optimum non-uniform q u a n t i z e r s were considered. The F o u r i e r and Hadamard coding schemes were evaluated i n terms of the mean square e r r o r between o r i g i n a l and r e c o n s t r u c t e d images, and by s u b j e c t i v e preference. Based on the t h e o r e t i c a l r e s u l t s , the Hadamard transform was s u p e r i o r to the F o u r i e r transform f o r b i t assignments below approximately 1.0 b i t s per p i c t u r e element ( b i t s / p e l . ) , on each of the Y, I and Q s i g n a l planes. The experimental r e s u l t s showed the Hadamard coded images to be s u p e r i o r to the F o u r i e r coded images from both the mean square e r r o r c r i t e r i o n and from a s u b j e c t i v e e v a l u a t i o n of the processed images. P i c t u r e s coded w i t h b l o c k s i z e s of 16 x 16 p i c t u r e elements were su p e r i o r