Image transmission system

• US 5,038,202 A
• Filed: 07/11/1989
• Issued: 08/06/1991
• Est. Priority Date: 05/13/1987
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Ooishi, Tsutomu, Ishikawa, Masaaki, Ishikawa, Yasunori, Suzuki, Koichi, Shimura, Hiroshi, Murayama, Noboru, Kuwata, Koji
• Primary Examiner(s): Shepperd, John W.
• Application Number:
  US07/378,059
• Time in Patent Office: 756 Days
• Field of Search: 358/13
• US Class Current: 348/396.1
• CPC Class Codes: H04N 7/148 Interfacing a video terminal to a particular transmission medium, e.g. ISDN

Abstract

An image transmission system includes a modulating part for independently modulating a luminance signal and two kinds of color difference signals and a demodulating part for independently demodulating the modulated luminance signal and the two kinds of modulated color difference signals. The demodulating part includes a signal correcting part for shifting at least one of the modulated luminance signal and the two kinds of modulated color difference signals by a predetermined number of picture elements in a scanning line direction to correct an error introduced by the modulation.

Claims

1. An image transmission system for transmitting an input color image data in a compressed and encoded form, said image transmission system comprising:

first converting means for converting said input color image data into a luminance signal and two kinds of color difference signals;

first modulator means for modulating said luminance signal into a modulated luminance signal; and

second modulator means for independently modulating said two kinds of color difference signals into two kinds of modulated color difference signals, said second modulator means modulating at least one of said two kinds of color difference signals according to a second modulation system different from a first modulation system used by said first modulator means, wherein said second modulator means uses an advanced adaptive delta modulation as said second modulation system, said advanced adaptive delta modulation having three modes of describing whether a first of two successive samples is greater than, equal to or smaller than a second of the two successive samples of one of said two kinds of color difference signals, said three modes comprising a first mode of indicating that said first sample is greater than said second sample, a second mode of indicating that said first sample is smaller than said second sample, and a third mode of indicating that said first and second samples are equal to each other,

said modulated luminance signal and said two kinds of modulated color difference signals being transmitted as said input color image data in the compressed and encoded form.

2. An image transmission system for transmitting an input color image data in a compressed and encoded form, said image transmission system comprising:

first converting means for converting said input color image data into a luminance signal and two kinds of color difference signals;

first modulator means for modulating said luminance signal into a modulated luminance signal; and

second modulator means for independently modulating said two kinds of color difference signals into two kinds of modulated color difference signals, said second modulator means modulating at least one of said two kinds of color difference signals according to a second modulation system different from a first modulation system used by said first modulator means, wherein said second modulator means includes;

(a) density buffer means for outputting a buffer value,

(b) adder means,

(c) subtracting means for subtracting the output buffer value of said density buffer means from an input density value to output a resulting difference value DF,

(d) first threshold output means for outputting a threshold value T,

(e) comparator means for comparing the difference value DF and the threshold value T and for producing an output signal of a first logic level when the difference value DF is greater than the threshold value T, an output signal of a second logic level when the difference value DF is smaller than -T which is complementary to the threshold value T, and an output signal of a logic level different from a logic level of an immediately preceding output signal when the difference value DF is less than or equal to the threshold value T and is greater than or equal to -T,

(f) second threshold output means for outputting a threshold value Ta,

(g) first counter means for counting a number of first logic levels of the output signal of said comparator means, and

(h) second counter means for counting a number of second logic levels of the output signal of said comparator means,

said first and second counter means outputting counted values thereof which determine the threshold value T to be read out from said first threshold output means and the threshold value Ta to be read out from said second threshold output means,

said first counter means being reset to zero when said second counter means receives the output signal of said comparator means having the second logic level,

said second counter means being reset to zero when said first counter means receives the output signal of said comparator having the first logic level,

said second threshold output means outputting the threshold value Ta to said adder means to be added to the output buffer value of said density buffer means,

said threshold value Ta read out from said second threshold output means being equal to zero when the counted value of one of said first and second counter means is zero and the counted value of the other of said first and second counter means is one,

said output signal of said comparator means being output as one of said two kinds of modulated color difference signals,

said modulated luminance signal and said two kinds of modulated color difference signals being transmitted as said input color image data in the compressed and encoded form.

3. The image transmission system as claimed in claim 2 wherein said first and second threshold output means are constituted by first and second tables, respectively, each of said first and second tables prestoring predetermined threshold values T and Ta.

4. The image transmission system as claimed in claim 3 wherein said first and second tables prestore said predetermined threshold values T and Ta independently for said two kinds of color difference signals.

5. An image transmission system for transmitting an input color image data in a compressed and encoded form, said image transmission system comprising:

first converting means for converting said input color image data into a luminance signal and two kinds of color difference signals;

first modulator means for modulating said luminance signal into a modulated luminance signal; and

second modulator means for independently modulating said two kinds of color difference signals into two kinds of modulated color difference signals, said second modulator means modulating at least one of said two kinds of color difference signals according to a second modulation system different from a first modulation system used by said first modulator means, wherein said second modulator means includes;

(a) first density buffer means for outputting a buffer value,

(b) first adder means,

(c) subtracting means for subtracting the output buffer value of said first density buffer means from an input density value to output a resulting difference value DF,

(d) first threshold output means for outputting a threshold value T,

(e) comparator means for comparing the difference value DF and the threshold value T and for producing an output signal of a first logic level when the difference value DF is greater than the threshold value T, an output signal of a second logic level when the difference value DF is smaller than -T which is complementary to the threshold value T, and an output signal of a logic level different from a logic level of an immediately preceding output signal when the difference value Dr is less than or equal to the threshold value T and is greater than or equal to -T,

(f) second threshold output means for outputting a threshold value Ta,

(g) first counter means for counting a number of first logic levels of the output signal of said comparator means, and

(h) second counter means for counting a number of second logic levels of the output signal of said comparator means,

said first and second counter means outputting counted values thereof which determine the threshold value T to be read out from said threshold output means and the threshold value Ta to be read out from said second threshold output means,

said first counter means being reset to zero when said second counter means receives the output signal of said comparator means having the second logic level,

said second counter means being reset to zero when said first counter means receives the output signal of said comparator having the first logic level,

said second threshold output means outputting the threshold value Ta to said first adder means to be added to the output buffer value of said first density buffer means,

said threshold value Ta read out from said second threshold output means being equal to zero when the counted value of one of said first and second counter means is zero and the counted value of the other of said first and second counter means is one,

said output signal of said comparator means being output as one of said two kinds of modulated color difference signals

said modulated luminance signal and said two kinds of modulated color difference signals being transmitted as said input color image data in the compressed and encoded form,

the image transmission system further including;

a transmission path through which said modulated luminance signal and said two kinds of modulated color difference signals are received;

demodulator means for independently demodulating said modulated luminance signal and said two kinds of modulated color difference signals received through said transmission path into a reproduced luminance signal and two kinds of reproduced color difference signals; and

second converting means for converting the reproduced luminance signal and the two kinds of reproduced color difference signals into a color image data approximating said input color image data.

6. The image transmission system as claimed in claim 5 wherein said second modulator means comprises thin-out means for thinning out said two kinds of color difference signals into two kinds of thinned out color difference signals before modulation thereof, and said demodulator means comprises interpolator means for interpolating the two kinds of reproduced thinned out color difference signals into said two kinds of reproduced color difference signals before demodulation thereof.

7. An image transmission system for transmitting an input color image data in a compressed and encoded form, said image transmission system comprising:

first converting means for converting said input color image data into a luminance signal and two kinds of color difference signals;

first modulator means for modulating said luminance signal into a modulated luminance signal; and

second modulator means for independently modulating said two kinds of color difference signals into two kinds of modulated color difference signals, said second modulator means modulating at least one of said two kinds of color difference signals according to a second modulation system different from a first modulation system used by said first modulator means, wherein said second modulator means includes;

(a) first density buffer means for outputting a buffer value,

(b) first adder means,

(c) subtracting means for subtracting the output buffer value of said first density buffer means from an input density value to output a resulting difference value DF,

(d) first threshold output means for outputting a threshold value T,

(e) comparator means for comparing the difference value DF and the threshold value T and for producing an output signal of a first logic level when the difference value DF is greater than the threshold value T, an output signal of a second logic level when the difference value DF is smaller than -T which is complementary to the threshold value T, and an output signal of a logic level different from a logic level of an immediately preceding output signal when the difference value Dr is less than or equal to the threshold value T and is greater than or equal to -T,

(f) second threshold output means for outputting a threshold value Ta,

(g) first counter means for counting a number of first logic levels of the output signal of said comparator means, and

(h) second counter means for counting a number of second logic levels of the output signal of said comparator means,

said first and second counter means outputting counted values thereof which determine the threshold value T to be read out from said first threshold output means and the threshold value Ta to be read out from said second threshold output means,

said first counter means being reset to zero when said second counter means receives the output signal of said comparator means having the second logic level,

said second counter means being reset to zero when said first counter means receives the output signal of said comparator having the first logic level,

said second threshold output means outputting the threshold value Ta to said first adder means to be added to the output buffer value of said first density buffer means,

said threshold value Ta read out from said second threshold output means being equal to zero when the counted value of one of said first and second counter means is zero and the counted value of the other of said first and second counter means is one,

said output signal of said comparator means being output as one of said two kinds of modulated color difference signals,

said modulated luminance signal and said two kinds of modulated color difference signals being transmitted as said input color image data in the compressed and encoded form.

8. The image transmission system as claimed in claim 7 wherein said demodulator means comprises third threshold output means, second adder means, second density buffer means, third counter means for counting a number of first logic levels of the output signal of said comparator means received through said transmission path, and fourth counter means for counting a number of second logic levels of the output signal of said comparator means received through said transmission path, said third and fourth counter means outputting counted values thereof which determine a threshold value Ta to be read out from said third threshold output means, said third counter means being reset to zero when said fourth counter means receives the output signal of said comparator means having the second logic level, said fourth counter means being reset to zero when said third counter means receives the output signal of said comparator having the first logic level, said third threshold output means outputting the threshold value Ta to said second adder means to be added to an output buffer value of said second density buffer means, the output buffer value of said second density buffer means being output as one of said two kinds of reproduced color difference signals.

9. An image transmission system for transmitting an input color data in a compressed and encoded form, the image transmission system comprising:

first converting means for converting said input color image data into a luminance signal and two kinds of color difference signals;

first modulator means for modulating said luminance signal into a modulated luminance signal;

second modulator means for independently modulating said two kinds of color difference signals into two kinds of modulated color difference signals, said second modulator means modulating at least one of said two kinds of color difference signals according to a second modulation system different from a first modulation system used by said first modulator means, said modulated luminance signal and said two kinds of modulated color difference signals being transmitted as said input color image data in the compressed and encoded form, wherein said first modulation system is a differential pulse code modulation and said second modulation system is an advanced adaptive delta modulation, said advanced adaptive delta modulation having three modes of describing whether a first of two successive samples is greater than, equal to or small than a second of the two successive samples of one of said two kinds of color difference signals, said three modes comprising a first mode of indicating that said first sample is greater than said second sample, a second mode of indicating that said first sample is smaller than said second sample, and a third mode of indicating that said first and second samples are equal to each other;

a transmission path through which said modulated luminance signal and said two kinds of modulated color difference signals are received;

demodulator means for independently demodulating said modulated luminance signal and said two kinds of modulated color difference signals received through said transmission path into a reproduced luminance signal and two kinds of reproduced color difference signals; and

second converting means for converting the reproduced luminance signal and the two kinds of reproduced color difference signals into color image data approximating said input color image data,

said demodulator means including signal correcting means for shifting at least one of the modulated luminance signal and the two kinds of modulated color difference signals by a predetermined number of picture elements in a scanning line direction before demodulation thereof.

10. The image transmission system as claimed in claim 9 wherein said signal converting means shifts the two kinds of modulated color difference signals by the predetermined number of picture elements.

11. The image transmission system as claimed in claim 10 wherein said second modulator means comprises thin-out means for thinning out said two kinds of color difference signals into two kinds of thinned out color difference signals before modulation thereof, and said demodulator means comprises interpolator means for interpolating the two kinds of reproduced thinned out color difference signals into said two kinds of reproduced color difference signals before demodulation thereof.