Shaded picture signal processing system and method

• US 4,366,507 A
• Filed: 01/19/1981
• Issued: 12/28/1982
• Est. Priority Date: 01/17/1980
• Status: Expired due to Term

• Current Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Mori, Sumio
• Primary Examiner(s): BRITTON, HOWARD W
• Application Number:
  US06/226,281
• Time in Patent Office: 708 Days
• Field of Search: 358/280, 358/282, 358/283, 358/284, 358/138, 364/515
• US Class Current: 358/3.26
• CPC Class Codes: H04N 1/40087 Multi-toning, i.e. converting a continuous-tone signal for reproduction with more than two discrete brightnesses or optical densities, e.g. dots of grey and black inks on white paper

Abstract

A shaded picture signal processing system and method which produces recorded pictures of high quality with a small number of gradation levels with the resolution of the picture maintained nearly unchanged. False contours appearing as quantization distortion are removed by dispersing noise of equal magnitude to the false contours throughout the whole picture or a specified portion of the picture so that the false contours cannot be detected by the human eye.

Claims

1. A shaded picture signal processing method for obtaining an output picture signal by quantizing an input picture signal having gradations of p bits per picture element into gradation levels of q bits per picture element with said input picture signal formed in a block of m×

n picture elements, comprising the steps of;

calculating a quantized value x_qij by quantizing in q bits per picture element x_ij in a spatial address (i, j) in said block;

calculating a higher quantization value x_uij by adding predetermined quantization step data to said quantized value x_qij ;

calculating a quantization error e_ij which is a difference between said picture element x_ij and said quantized value x_qij ; and

providing a threshold pattern in m×

n matrix form in correspondence to said one block;

selecting one of said quantized value x_qij and said higher quantization value x_uij in response to a comparison of said quantization error e_ij with a threshold c_ij at a spatial address (i, j) in said threshold pattern to output an output picture signal y_ij of q bits per picture element corresponding to said spatial address thereby to reproduce halftones.

3. The system as claimed in claim 1 or 2 wherein said quantization step data is set to 2.sup.(p-q).

4. The system as claimed in claim 1 or 2 wherein said threshold c_ij in said threshold pattern is fixed independent of input picture signals.

5. The system as claimed in claim 1 or 2 wherein said threshold pattern is varied according to the magnitudes of said picture elements x_ij in said block so as to be suitably variable for blocks.

2. A shaded picture signal processing method in which an input picture signal is formed in a block m×

n picture elements, comprising the steps of;

calculating an average value x from picture elements x_ij of said block;

dividing said block into a region A in which picture elements x_ij ≧

average value x and a region B in which picture elements x_ij <

average value x;

calculating average values x₁ and x₀ of said picture elements x_ij in said regions A and B;

calculating quantized values x_1q and x_0q by quantizing in q bits said average values x₁ and x₀ ;

calculating higher quantization values x_1u and x_0u obtained by adding said quantized values x_1q and x_0q to predetermined quantization step data;

calculating quantization errors e₁ and e₀ which are differences between said average value x₁ and said quantized value x_1q and between said average value x₀ and said quantized value x_0q ;

providing a threshold pattern in m×

n matrix form in correspondence to said block; and

obtaining an output picture signal y_ij in which each picture element comprises q bits corresponding to a spatial address (i, j) in said threshold pattern by selecting one of said quantized value and higher quantization value by comparing said quantization error with a threshold c_ij in said spatial address, wherein, when said spatial address (i, j) is in said region A said quantization error e₁, quantized value x_1q and higher quantization value x_1u are employed and when said spatial address is in said region B, said quantization error e₀, quantized value x₀ q and quantization higher value x_0u are employed; and

outputting one of said quantized value x_1q and quantization higher value x_1u, and said quantized value x_0q and quantization higher value x_0u to reproduce halftones.