Image signal processing apparatus

An image signal processing apparatus of the present invention is an apparatus to process image signal, wherein an input image signal is corrected and made into a sharp and visually preferred image signal through such composition that an outline correction signal which has been non-linearly processed corresponding to the outline section of the input image signal is formed, the formed outline section correcting signal is added to the delayed image signal to be output.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image signal processing apparatus to 
process an image signal. 
2. Related Background Art 
There is already known an image signal processing apparatus which improves 
the image quality of TV image receiver as the image signal processing 
apparatus. 
As the method to improve picture quality of TV image receiver, there is 
known the method to improve picture quality by improving the frequency 
characteristics of the image amplifying circuit or by the system of delay 
type outline correction circuit. 
FIG. 1 indicates the example of the basic composition of the conventional 
outline correction circuit. 
In FIG. 1, the input image signal receives adjustment of brightness and 
contrast at the brightness/contrast adjusting circuit 1 and then it is 
supplied to the outline signal forming circuit 2 and delay circuit 3. 
At outline signal forming circuit 2, the signals corresponding to the 
outline section of the image among all the input signals of the image are 
extracted and they are supplied to the gain control circuit 4 at the later 
stage. 
Gain control circuit 4 is so constructed that it can control the gain of 
the outline signal which is supplied by the operating unit not shown in 
the drawing and the outline signal with thus controlled gain is supplied 
to the adder 5. 
To the adder 5 is also supplied the image signal whose brightness and 
contrast have been adjusted by the brightness/contrast adjusting circuit 
1, after being delayed for preset time by the delay circuit 3 and by 
further addition of the outline signal supplied by the gain control 
circuit 4 and the image signal supplied by the delay circuit 3, the image 
signal with corrected outline is output at the said adder 5. 
FIG. 2 shows an example of the composition of horizontal outline correction 
circuit while FIG. 3 is the drawing to indicate the signal waveform of the 
unit with the composition shown in FIG. 2. 
In FIG. 2, image input signal (A) gives the image signal output to which 
the outline signal shown in FIG. 3(G) has been added by the delay circuit 
7, 10, 13, coefficient multiplier 6, 8, 11 and adder 9, 12, 14. 
However with the aforesaid conventional outline correction circuit, when 
certain correction amount is set, the same outline correction is made 
irrespective of the brightness level (dark part, bright part) of the image 
signal and consequently, should the outline be over-emphasized, outline 
emphasis becomes too remarkable at dark scene producing glittering image, 
while at the bright scene, particularly where white letter etc. is 
produced, Braun's tube becomes in the state of blooming and such 
phenomenon as white collapse occurs, resulting in the deterioration of 
picture quality. 
Further more, in the case of the TV receiver, when signal processing is 
executed when the signals are in analogue state in the modulation of 
scanning speed of electron beam of image receiving tube by the outline 
signal formed by the input image signal, in order to improve sharpness of 
the image, it is unavoidable that the system becomes costly due to 
employment of many delay lines, differential circuits etc. and performance 
becomes unstable due to the fluctuation of temperature, humidity or 
degeneration occurring with elapse of time. 
A method to emphasize the outline of the image by digitalizing the image 
signal, has been proposed by Japanese Patent Application Laid-Open No. 
59-23974. 
However in the case of such conventional method, a delay circuit where 
plural number of delay signals each of which is deviated in timing by one 
horizontal scanning period is employed, the correlation of plural number 
of delay signals output by the said delay circuit is calculated and the 
signals corresponding to such correlation are output, thus plural number 
of costly line memories are required, resulting in the increase of cost 
and besides, since outline emphasis is made corresponding to such 
correlations by calculating the correlation between image signals in each 
horizontal scanning period, such problem occurs that sufficient outline 
emphasis can not be made depending on the contents of the image. 
SUMMARY OF THE INVENTION 
The objective of the present invention is to provide the image signal 
processing apparatus which can solve the aforesaid problems. 
An object of the present invention is to provide the image signal 
processing apparatus which can correct the image signal into such image 
signal as having visually preferred picture quality. 
For such object, the present invention takes an embodiment of the present 
invention wherein; 
the image signal processing apparatus is presented which comprises the 
means for inputting an image signal, forming and outputting the outline 
part correction signal having been given with non-linear processing 
corresponding to the outline part of the input image signal, delay means 
for inputting an image signal and delaying and outputting the input image 
signal and adder means for adding the outline part correction signal which 
has been output by the outline part correction signal generating means to 
the image signal output by the delay means. 
Still other object of the present invention is to provide an image signal 
processing apparatus which can execute outline emphasis processing of the 
image in proportion to the image signal. 
For such object, the present invention proposes an image signal processing 
apparatus as an embodiment, comprising; a non-linear means for inputting 
image signal, non-linearly processing the input image signal and 
outputting it, outline part signal forming means for forming the signal of 
outline part from the signal to be output by the non-linear means; delay 
means for inputting the image signal and delaying the input image signal 
so that it should synchronize with the timing at which outline part signal 
corresponding to the image signal is output by the said outline part 
signal forming means and for outputting it and the adding means for adding 
the outline part signal output by the output part signal forming means on 
the image signal to be output by the delay signal and output the result of 
such addition. 
Still another object of the present invention is to provide an image signal 
processing apparatus which can execute outline emphasis processing of the 
image signal without relying on the correlation of the images. 
The image signal processing apparatus of the present invention which 
processes an image signal, comprises analogue/digital conversion means for 
inputting the image signal, forming the image data by sampling the input 
image signal by the preset sampling frequency and digitalizing it and for 
outputting such image data; delay means for delaying, for preset period, 
the image data output by the analogue/digital converter means and for 
outputting such data; correction data generating means for forming the 
correction data according to the image data corresponding to the 
difference between the image data output by the analogue/digital 
conversion means and the image data output by said delay means and for 
outputting such correction data; adding means for adding the image data 
output by the delay means to the correction data output by the correction 
data forming means and for outputting such data and the digital/analogue 
conversion means for converting the image data output by the adding means 
into analogue signal and for outputting it. 
Still another object of the present invention is to provide an image signal 
processing apparatus which can display the image with high degree of 
sharpness. 
The image signal processing apparatus of the present invention which 
processes an image signal comprises; analogue/digital conversion device 
for inputting the image signal, for forming image data by sampling the 
input image signal by the preset sampling frequency and digitalizing it 
and for outputting such data; delay means for delaying, for preset period, 
the image data output by the analogue/digital converting means and for 
outputting such delayed data; the correction signal generating means for 
forming correction signal using the image data corresponding to said 
differential value according to the difference between the image data 
output by the analogue/digital conversion means and the image data output 
by said delay means and for outputting such correction signal; 
analogue/digital conversion means for converting the image data output by 
the delay means into analogue signal and for outputting it and the display 
device in which the formation speed of said scanning line is modulated by 
the correction signal output by the correction signal generating means at 
the time when the scanning line corresponding to the image signal output 
by the digital/analogue conversion means is formed. 
The objects of the present invention other than the above and their 
characteristics shall be made clear by the detailed descriptions of the 
form of the invention in reference to the drawings that follow hereunder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention shall be described in reference to the embodiment. 
FIG. 4 shows the composition of the outline correction circuit representing 
the first embodiment. In FIG. 4, element 1 is bright contrast adjusting 
circuit, 2 is profile signal formation circuit, 3 is delay circuit, 5 is 
adder and 15 is non-linear circuit. 
In FIG. 4, the input image signal is supplied to the brightness/contrast 
adjusting circuit 1 to execute adjustment of brightness and contrast. The 
image signal A which is given by such adjustment of brightness and 
contrast is fed to the non-linear circuit 15 and delay circuit 3 and the 
image signal F which has been delayed by 3 is supplied to adder 5. 
Non-linear circuit 15 has the non-linear characteristics as shown in FIG. 
5A and assuming that the stepped waveform image signal as shown in FIG. 5B 
is supplied to the said non-linear circuit 15, the image signal having the 
waveform as shown in FIG. 5C is output by the said non-linear circuit 15. 
As stated above, the image signal given out by the non-linear circuit 15 
has such characteristics that, as shown in FIG. 5C, the signal level is 
compressed for the signal indicating the dark area of the image (i.e., the 
area where signal level is small) and the signal indicating the bright 
area of the image (i.e., the area where signal level is large), while the 
signal level is expanded for the signal indicating the area where the 
brightness of the image is medium (i.e., at around the area where signal 
level is medium). 
The image signal indicated in FIG. 5C is supplied to the outline signal 
forming circuit 2 and outline signal E as shown in FIG. 5D is output by 
the outline signal forming circuit 2 and fed to the adder 5. 
At adder 5, by adding the outline signal E supplied by outline signal 
forming circuit 2 and the image signal F delayed for certain time by the 
delay circuit 3, the image signal G of which the outline is emphasized as 
shown in FIG. 5E is output. 
As stated above, by providing the non-linear circuit 15 prior to the 
outline signal forming circuit 2, it is possible to suppress the amount of 
outline emphasis for the signals representing the dark part and bright 
part of the image and realize the optimum outline emphasis in a wide range 
from dark scene to the bright scene of the image and thus glittering in 
the dark scene or blooming (smashing of white or blurr) in the bright 
scene etc. are prevented and at the scene where the brightness is normal, 
an appropriate emphasis of the outline obtained. 
In FIG. 1, the elements which are equivalent in the composition to those of 
FIG. 1 are given the same code number. 
Hereunder is described another embodiment of the present invention. 
FIG. 6 is the drawing to show the composition of the outline correction 
circuit of such other embodiment. In FIG. 6, element 15 is a non-linear 
circuit; 20 is an amplifier, 21, 22 are differential circuit; 22 is 
reversal amplifier; 24 is delay circuit and 25 is adder. 
In FIG. 6, image input signal A (see FIG. 7B) is given the signal waveform 
as shown in FIG. 7C by the non-linear circuit having the charateristics 
shown in FIG. 7A, amplified by amplifier 20, supplied to the outline 
signal forming circuit 26 which is composed of differential circuit 21, 23 
and reversal amplifier 22 and the signal with such waveform as shown by 
FIG. 7C is formed by the said outline siganl forming circuit 26. On the 
other hand, input image signal A is delayed by the delay circuit 24 and 
supplied to adder 25. 
As stated above, the output signal M of the outline signal forming circuit 
26 (see FIG. 7E) and output signal N of delay circuit 24 (see FIG. 7F) are 
supplied to adder 25 and by adding these two, the image signal P (see FIG. 
7G) which had been given the outline correction is obtained. As shown in 
FIG. 7G, according to the present embodiment, overshoot (c in the Figure) 
and preshoot (b in the Figure) are added to the input image signal and 
thus it is possible to display the image with even better sharpness. 
As described above, under the outline correction system for improvement of 
picture quality of TV receiver, the degeneration of apparent picture 
quality caused by the change of the size of the signal input, for example, 
over-emphasis of the outline in the dark scene or blooming phenomenon in 
the bright scene is suppressed and in the ordinary case, dynamic outline 
correction is automatically executed such as sufficient outline emphasis 
and as the result, it is possible to always display the image of preferred 
quality. 
Hereunder is described the second embodiment of the present invention. 
FIG. 8 is the drawing to show the composition of the outline correction 
circuit representing the second embodiment of the present invention. In 
FIG. 8, element 11 is the input terminal of image signal; 12 is the 
low-pass filter (LPF) for limiting the hand width to digitalize image 
signal; 13 is the analogue/ditigal (A/D) converter to change analogue 
signal into digital signal; 14 is the converter table to change digital 
signal into other digital signal which has the non-linear chracteristics 
and is composed of RAM (random access memory) to enable rewriting of the 
value of conversion table (non-linear characteristics). 
Element 15 is the control unit to supply the data for rewriting the value 
of the aforesaid conversion table 14 in order to obtain the outline 
emphasis preferred by the operator. 
Element 16 is the difference detection data processing circuit which 
compares the present image data with the image data one sample period 
prior thereto, forms the differential value data and when thus formed 
differential value data are smaller than the preset differential value 
level or when the polarity of the differential value data is reversed, 
adds the data of the same value but with reversed polarity to the said 
differential value data at the timing one sample period delayed; 17 is the 
adder circuit to add the differential value data output by the said 
difference detection data processing circuit 16 to the image data delayed 
by the delay circuit 11 to be stated later; 18 is the limiter circuit 
which prevents the image data output by the said adder circuit 17 exceed 
the black level peak (i.e., minimum value) or white level peak (i.e., 
maximum value), 19 is the digital/analogue (D/A) converter to convert the 
image data output by the said limiter circuit 18 into analogue signals; 20 
is the low pass filter to limit the image signal to be output by the said 
D/A converter 19 within the desired band width and 21 is the delay circuit 
to delay the image data by one sample period. 
In FIG. 8, the band width of the image signal input by input terminal 11 is 
limited within the desired range by LPF12 and then it is converted into 
digital signal by A/D converter 13 and supplied to the difference 
detection data processing circuit 16. 
The difference detection data processing circuit 16 receives the present 
image data supplied by the said A/D converter 13 and the image data one 
sample period prior thereto which have been delayed by one sample period 
by the circuit 21 and the differential value data are comparatively 
detected. 
As shown in FIG. 10, differential value data C (except the part marked by 
diagonal lines in the figure) is obtained by subtracting the present image 
data A from the image data B which have been delayed by one sample period. 
(T.sub.1, T.sub.2, T.sub.3, T.sub.4 and T.sub.11 . . . T.sub.14 in the 
figure indicate the timing of sampling). 
Differential value data obtained from difference detection data processing 
circuit 16 of FIG. 8 are given non-linear conversion according to the 
conversion table 14. Non-linear conversion characteristics of the said 
conversion table 14 are such that, as shown in FIG. 9, when the level of 
the differential value data is lower than D.sub.1 in the figure, it is 
converted into the conversion value data indicating "0" and when the level 
of the said differential value data is higher than D.sub.2 in the figure, 
they are converted into the conversion value data indicating the preset 
level. 
Non-linear characteristics of the conversion table 14 use the RAM (random 
access memory) so that the composition can be changed in such way that 
they fit the outline emphasis level preferred by the operator according to 
the instruction given by the control unit 15. 
When the differential value data formed by the difference detection data 
circuit 16 and conversion table 14 (FIG. 10C) are lower than the preset 
differential value level or their polarity is reversed, the data with the 
same level but with the reversed polarity to such differential value are 
added thereto at the timing one sample period later and they are output at 
the difference detection data processing circuit 16. 
In other words, the difference detection data processing circuit 16 outputs 
the differential value data added with the part marked by diagonal lines 
in FIG. 10C. Such differential value data C are supplied to the adder 
circuit 7 while to such adder circuit 17 are already added the image data 
B having been delayed for one sample period by the delay circuit 21 and by 
addition of these two data, the image data D which are emphasized of the 
outline are formed and they are supplied to the limiter circuit 18. 
At the limiter circuit 18, the image data are so limited that they become 
in between the white peak level (i.e., the maximum value of image data) 
and the black peak level (i.e., the minimum value of image data or when 
the said image data include the data obtained by digitalizing the 
synchronized signals, the value level which is lower than the pedestal 
level shown by the image data but within the range where synchronization 
does not become unstable) and thus limited data are output, converted into 
analogue signal at D/A converter 19, limited by LPE20 for their band and 
are output as the image signals with emphasized outline. 
FIG. 11 shows the signal waveforms at various units when the image signals 
having medium range frequency band and rising radically are input into the 
device shown in FIG. 8, while FIG. 12 shows the signal waveforms at 
various units when the image signals having the frequency band lower than 
the image signals indicated in FIG. 11 and rising moderately are input. As 
shown in FIG. 12, outline emphasis is not made on the moderately canning 
image signals and therefore there is no change of deterioration of picture 
quality. 
As explained above, by employing such composition that after digitalizing 
the image signals, the differential value between the present image data 
and the image data one sample period before is detected and outline 
emphasis is given according to the level of thus detected differential 
value, a high quality outline emphasis can be made at low cost without 
relying on the correlation between the horizontal scanning periods of the 
image signal. 
Hereunder is described the embodiment 3 of the present invention. 
FIG. 13 is the drawing to show the schematic composition of the TV image 
receiver to which the present invention has been applied, which represents 
the third embodiment of the present invention while FIG. 14 is the timing 
chart to describe the performance of the composition of the said FIG. 13. 
In FIG. 13, the element 31 is the image signal input terminal; 32 is the 
low pass filter (LPF) which, at the digitalization of the input image 
signal, limits the said image signal into the desired band; 33 is the 
analogue/digital (A/D) converter and 34 is the delay device to delay the 
digital signal output by said A/D converter 33 which comprises for example 
a memory. 
Element 35 is the subtractor to obtain the differential value between the 
digital signal formed at the said A/D converter 33 and the digital signal 
formed one sampling period before; 36 is the data conversion unit to 
convert the difference value output by the said subtractor 35 based on the 
conversion data memorized at the conversion table 37 which is stated 
later; 37 is the conversion table memorizing the conversion data used for 
non-linear conversion of the difference value output by the said 
subtractor 35, the said conversion table being composed of RAM (Random 
Access Memory). 
Element 38 is the control unit to instruct rewriting of the conversion data 
to be memorized by the said conversion table 37 in order to obtain the 
picture quality designated by the operator; 39 is the digital/analogue 
(D/A) converter to convert the signal having been given non-linear 
conversion by the said data conversion unit 36 into analogue signal; 40 is 
the low pass filter (LPF) which limits the band of the signal output by 
the said D/A converter 39 into the desired band; 41 is the adder to add 
the signal output by the said LPF40 and the sawteeth wave signal for 
horizontal deflection; 42 is the digital/analogue (D/A) converter to 
convert the digital signal delayed by delay device 34 into analogue 
signal; 43 is the low pass filter (LPF) to limit the band of the signal 
output by the said D/A converter into the desired band; 44 is the 
deflection coil to deflect the electron beam modulated by the image 
signal; 45 is the image receiving tube (CRT) to display the image 
corresponding to the image singal. 
Hereunder is described the performance of the composition shown in FIG. 13. 
In FIG. 13, the image signal input by the input terminal 31 is limited to 
the desired band by LPF32 and converted into digital signal by the A/D 
converter 33 which functions in synchronization with the sampling timing 
(T.sub.1, T.sub.2, T.sub.3 . . . in the figure) shown in FIG. 14 and the 
image data output by the said A/D converter 33 (see FIG. 14a) are supplied 
to the subtractor 35 and delay device 34. 
Then, the differential value (see FIG. 14(c)) between the signal being 
output by A/D converter 33 and the signal delayed for one sampling period 
by the said delay device 34 (see FIG. 14(b)) is output at the said 
subtractor 35. 
Differential value data output by the said subtractor 35 are the data 
non-linearly converted by the data conversion unit 36 based on the 
conversion data memorized by the conversion table 37. 
Here, the characteristic example of non-linear conversion according to the 
conversion table 37 of FIG. 13 shall be identical with the characteristics 
shown in FIG. 9 of the aforesaid embodiment 13. 
As shown in the aforesaid FIG. 9, non-linear conversion characteristics of 
the said conversion table 37 are such that when the level of the 
differential value data supplied is larger than the preset value (D.sub.2 
in the figure), conversion value data of preset level is output. 
The said conversion table 37 is composed of RAM stated above and it is so 
arranged that the conversion data which determines the non-linear 
characteristics according to the instruction of the control unit 38 of 
FIG. 13 can be rewritten and it is possible to set the conversion data 
according to the instruction of the operator. 
As the aforesaid data conversion unit 36, the differential value data 
non-linearly converted according to the conversion data memorized by the 
said conversion table 37 are added to the differential value data 
non-linearly converted as aforesaid, delayed by one sampling period and 
having the signal waveform with reversed polarity (see FIG. 14(d)). 
As aforesaid, the signal formed at the said data conversion unit 36 is 
converted into an analogue signal by D/A converter 39, its band being 
limited by LPF40 and added with the sawteeth wave signal for horizontal 
deflection at adder 41 (see FIG. 14(e)) and supplied to deflection coil 
44. 
On the other hand, the image data being output by the said delay device 34 
is converted into analogue signal by D/A converter 42, its band being 
limited by LPF43 and supplied to CRT45 while the electron beam modulated 
by the image signal output by the said LPF43 is horizontally deflected by 
the said deflection coil 44. 
As aforesaid, by modulating the scanning speed of electron beam of CRT, the 
difference in brightness becomes clearer at the part where the brightness 
components of the image signal radially change and thus the shapness of 
the image indicated by CRT increases. 
As shown in the present embodiment, by so constructing the system that the 
input image signals are processed digitally, the action timing of the 
device is controlled to be synchronized with the sampling block and the 
action becomes extremely stable while by rewriting the contents of 
conversion table memorizing the conversion data for setting the non-linear 
characteristics which determine the sharpness, the picture quality 
designated by the operator is easily obtained. 
In the case of the TV signal receiver used in recent years, employment of 
digital system has considerably advanced and therefore it is possible to 
increase the sharpness of image displayed on CRT by a simple composition 
without increasing the cost, only by addition of delay device 34, 
subtractor 35, data converter 36, conversion table 37 and control unit 38 
etc. as shown in FIG. 13. 
As described above, according to the present embodiment, it is possible to 
provide a TV receiver which can display the TV image of high sharpness 
with stability by a simple and low cost composition.