EP0868817A2 - Amelioration de la finesse - Google Patents

Amelioration de la finesse

Info

Publication number
EP0868817A2
EP0868817A2 EP97940279A EP97940279A EP0868817A2 EP 0868817 A2 EP0868817 A2 EP 0868817A2 EP 97940279 A EP97940279 A EP 97940279A EP 97940279 A EP97940279 A EP 97940279A EP 0868817 A2 EP0868817 A2 EP 0868817A2
Authority
EP
European Patent Office
Prior art keywords
sharpness
signal
ctrl
control signal
enhancing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97940279A
Other languages
German (de)
English (en)
Inventor
Michel Wouter Nieuwenhuizen
Leendert Albertus Dick Van Den Broeke
Maarten Wilhelmus Henricus Marie Van Dommelen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP97940279A priority Critical patent/EP0868817A2/fr
Publication of EP0868817A2 publication Critical patent/EP0868817A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/77—Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/646—Circuits for processing colour signals for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters

Definitions

  • the invention relates to a method of and a circuit for sharpness improvement, and to an image display apparatus and a multi-media apparatus comprising such a sharpness improvement circuit.
  • a first aspect of the invention provides a method as defined in claim 1.
  • a second aspect of the invention provides a sharpness improving circuit as defined in claim 9.
  • Third and fourth aspects of the invention provide an image display apparatus and a multi-media apparatus comprising such a sharpness improvement circuit.
  • the presence of predetermined colors in an image signal is determined to obtain a control signal, and a sharpness of the image signal is enhanced in dependence upon the control signal.
  • the picture quality of TV signals is improved by applying peaking to the luminance channel in dependence upon the color information to enhance the sharpness perception of red and magenta parts in the image.
  • Fig. 1 shows a basic block diagram of a first embodiment of the invention
  • Fig. 2 illustrates a first possible sharpness detection area
  • Fig. 3 illustrates a preferred sharpness detection area
  • Fig. 4 shows a possible realization of a peaking filter
  • Fig. 5 shows a preferred embodiment of an image display apparatus in accordance with the present invention
  • Fig. 6 shows a multi-media apparatus in accordance with the present invention.
  • Fig. 7 shows a preferred embodiment of a color-dependent sharpness improvement circuit in accordance with the present invention.
  • a primary aspect of the invention aims at increasing the perceived sharpness of saturated red, magenta and blue.
  • the circuit increases the luminance sharpness in saturated red and magenta parts of the screen.
  • the visible results are positive (blue is not enhanced, because there is very little detail in blue in natural scenes, so only noise is enhanced).
  • the circuit can easily be implemented in an IC.
  • the camera sensor decomposes the picture into three primary colors: R, G and B.
  • the 1/7 pre-correction is added immediately after the sensor and before the matrixing of the signals into three signals which are suited for efficient transfer: Y, U and V.
  • these signals are de-matrixed into the original R, G and B and displayed on the inherently non-linear CRT.
  • This constant luminance defect is important because the perceived sharpness impression of a picture is predominantly determined by the luminance information. So, if part of the luminance information is transmitted via the chroma channels U and V, the luminance bandwidth will be less than is ideally expected. This results in a blurred image in saturated blue, magenta and red parts.
  • the invention is further based on the recognition that it is possible to improve the picture by means of the following algorithm: detect where there is red, blue or magenta in the picture and improve the sharpness of the color signals locally. Since the chrominance signals are band-limited to approximately 700 kHz, it is no use increasing the high frequencies of the chrominance signals (they are simply not there). Instead, the luminance sharpness must be increased if the enhancement is effected in the YUV domain. While it is conceivable to enhance the sharpness of the color signals in the RGB domain, sharpness enhancement of the luminance signal is preferred for cost considerations.
  • the extra gain is preferably applied for relatively low frequencies (i.e. 700 kHz to 2 MHz, while prior art peaking commonly affects the frequency range between 2 and 4 MHz). This is desired because the information that is lacking starts at approximately 700 kHz. Above 2 MHz, the influence of this feature turns out to be less important. Near the color subcarrier, the effect should be negligible to avoid amplification of cross-luminance effects.
  • the sharpness enhancement of the present invention is preferably used in addition to existing sharpness enhancement algorithms. While the existing algorithms are generally satisfactory for enhancing the luminance sharpness, they are insufficiently effective in red, magenta and blue. As for these colors, the existing algorithms mainly boost noise because they peak at a too high frequency. If this peaking were optimized for (saturated) red, magenta and blue, the corresponding parts of the image would be improved, while the other parts (grey, green and yellow) would become very ugly. Consequently, use of a conventional sharpness enhancement for all colors is preferred and, in addition thereto, the enhancement proposed by the present invention for at least the colors red and magenta.
  • Fig. 1 shows a basic block diagram of a first embodiment of a sharpness improvement circuit SI in accordance with the present invention.
  • a luminance component y- in of an input image signal is applied to a peaking circuit 1 which may comprise a second derivative-obtaining circuit.
  • a peaking signal output of the peaking circuit 1 is multiplied by a control signal CTRL by means of a multiplier 3, and subsequently added to the input luminance component y-in by an adder 5 to produce an output luminance component y-out.
  • the control signal CTRL is derived from input chrominance components u-in and v-in of the image signal by a color detector 7 which detects at least the colors red and magenta, and possibly also the color blue.
  • the chrominance components u-in and v-in are supplied unchanged at outputs u-out and v-out, respectively.
  • Fig. 2 illustrates a first possible sharpness detection area in a color diagram determined by the chrominance components B-Y on the horizontal axis and R-Y on the vertical axis.
  • the colors red (R), magenta (M), blue (B), cyan (C), green (G), and yellow (Y) are indicated at the corners of the color diagram.
  • Fig. 2 shows how the U and V signals span the color plane. If one wants to detect red, blue and magenta, it is clear that a detection area could look like the shaded area. This area can be described as: (B-Y)/2.03 + (R-Y)/l .14 > . 0.
  • the cross-over between detected and non-detected colors is preferably gradual. It is also important that colorless areas are not detected because this would lead to a sharpening of grey-tones, which is not wanted with the color-specific algorithm of the present invention.
  • Fig. 3 illustrates a preferred sharpness detection area, which no longer contains the color blue.
  • Fig. 4 shows a possible realization of the peaking filter 1 of Fig. 1.
  • the input luminance component y-in is applied to a cascade connection of two delay cells 11, 13.
  • An input of the delay cell 11 and outputs of the delay cells 11 and 13 are connected to respective inputs of an adder 21 thru a multiplier 15 multiplying by -0.5, a multiplier 17 multiplying by 1, and a multiplier 19 multiplying by -0.5, respectively.
  • the multiplier 17 may be a direct connection.
  • An output of the adder 21 furnishes the peaking signal output.
  • the peaking circuit of Fig. 4 is a simple -1/2, 1, -1/2 FIR filter.
  • the length of the delay line determines the peaking frequency. This should be chosen to complement the chroma bandwidth of 700 kHz.
  • the optimal peaking frequency is around 1.5 MHz.
  • a delay time per cell of approximately 250 ns was used for a prototype. Probably a slightly longer delay might be chosen for an optimum result.
  • Those skilled in the art may wish to replace the peaking filter of Fig. 4 by other peaking filters.
  • the amount of peaking can be controlled by multiplying the peaking signal with the control signal CTRL. If the control signal CTRL is zero, there is no peaking. If the control signal CTRL is 1, the peaking is maximum.
  • Fig. 5 shows a preferred embodiment of an image display apparatus in accordance with the present invention.
  • the input components y-in, u-in and v-in are clamped by clamping circuits 23, 25 and 27, respectively.
  • the clamped luminance component y-in is applied to the peaking filter of Fig. 4.
  • the clamped chrominance components u-in and v-in are applied to multipliers 41 and 43, respectively, after having been subjected to compensating delays in delay cells 29 and 31, respectively.
  • the outputs of the multipliers 41 and 43 are summed by an adder 45.
  • the compensating delay cells 29 and 31 furnish the output chrominance components u-out and v-out, respectively.
  • the embodiment of Fig. 5 corresponds to formula (1); in an embodiment which corresponds to formula (2), the elements 41-49 have to be replaced by another processor which calculates CTRL on the basis of U and V.
  • the output components y-out, u-out and v-out are applied to a matrix circuit MX which furnishes red, green and blue color signals.
  • the R, G and B color signals are processed by a red processor RP, a green processor GP and a blue processor BP, respectively.
  • Output signals of the color processors RP, GP and BP are applied to a display tube DT.
  • Fig. 5 the actual color detector 7 of Fig. 1 has been drawn in some more detail.
  • the sum of U and V is compared with Vref in the soft comparator 49.
  • this comparator is made with a long-tailed pair, which yields a cross-over region of approximately 250 mV. This is sufficient for a gradual cross-over between detected and non-detected colors.
  • V ref the additional clamp 47 between the U and V adder 45 and the soft comparator 49 is desired for correct DC biasing.
  • Fig. 6 shows a multi-media apparatus in accordance with the present invention.
  • the multi-media apparatus has an input 61 for receiving image signals to be processed by an image processor (IP) 63 comprising a sharpness improvement circuit SI of the type shown in Fig. 1.
  • IP image processor
  • a CD-ROM player 65 is present for providing image and/or data signals II and sound signals S
  • a sound-processing unit (part SND1 of a sound card) 69 receives sound signals from an input 67, and furnishes data signals Dl and sound signals S2.
  • Another processor 73 operates on text signals (TXT) received from a keyboard connector 71.
  • TXT text signals
  • Image and/or data outputs of the devices 63, 65, 69 and 73 are applied to a video unit (graphics card) 75 which furnishes an output video signal to an output 77 to which a monitor (not shown) can be connected.
  • Sound outputs SI and S2 of the CD-ROM player 65 and the sound-processing unit 69 are connected to an output part SND2 of the sound card, whose output is connected to a sound output of the multi-media apparatus.
  • Fig. 7 shows a preferred embodiment of a color-dependent sharpness improvement circuit in accordance with the present invention.
  • the signals Y0, Y4 and Y8 are applied to the low-frequency peaking filter 1.
  • a coring circuit 91 and a switch 93 are placed between the peaking filter 1 and the fader 3 which is controlled by the color-dependent sharpness control signal CTRL.
  • the switch 93 is controlled by a control signal CDS indicating whether the color-dependent sharpness control in accordance with the present invention is desired.
  • a second fader 107 is placed between the fader 3 and the adder 5.
  • the signals Yl, Y2, Y4, Y6 and Y7 are applied to a high-frequency peaking filter 94 which is followed by a coring circuit 95 and a fader 97.
  • a control signal CFS applied to the high-frequency peaking filter 94, a selection is made between a 2.38 MHz peaking frequency and a 3.58 MHz peaking frequency.
  • the detected amplitude AMP is used to control the faders 97 and 107 via comparators 103 and 105, respectively.
  • the purpose of the amplitude-dependent control of the peaking is to prevent spot blooming, resulting in reduced sharpness, from occurring as a result of a too large sharpness enhancement signal.
  • the faders 97 and 107 are controlled by the detected amplitude AMP in such a manner that the output signal will never exceed 110% of the maximum input signal amplitude.
  • Offset voltage sources 107-111 provide three different offset voltages between which a selection is made by a switch 113 in dependence upon the control signals CDS (indicating whether color-dependent sharpness control is desired) and CFS (indicating the peaking frequency of the high-frequency peaking filter 94).
  • CDS color-dependent sharpness control
  • CFS peaking frequency of the high-frequency peaking filter 94
  • the offset voltage selected by the switch 113 is applied to the comparator 103, while a fourth offset voltage is applied to the comparator 105 by offset voltage source 115.
  • These different offsets are desired because the detected amplitude AMP is slightly frequency-dependent, so that AMP should be adjusted in dependence upon CFS. Obviously, if the color-dependent sharpness improvement is switched on, the correction in dependence upon AMP should be adjusted, which explains the CDS-dependent control of switch 113.
  • a further modification between the embodiment of Fig. 7 and that of Fig. 5 is that minimum detection arrangements 117-119 and 121-123 are inserted before the multipliers 41 and 43, respectively.
  • Each minimum detection arrangements comprises a series connection of two delay cells 117, 118 and 121, 122, and a minimum detection circuit 119, 123 which selects the minimum of the received chrominance signal u-in, v-in and the once and twice delayed chrominance signals supplied by the delay cells.
  • These minimum detection arrangements serve to ensure that the color-dependent sharpness control is only effective for sharpening the high-frequency components within a colored object, while undesired overshoots are prevented from occurring at the boundaries of colored objects.
  • the sharpness improvement algorithm was tested on a test signal having several highly saturated red, blue and magenta areas.
  • the first conclusions are: the circuit works well and gives the reproduction of saturated red and magenta a more pleasing effect with both PAL and NTSC signals.
  • the sharpness of saturated parts is increased. There seem to be few cases where there is saturated blue with a lot of details. Most of the blue is water or sky, so that a possible increase of noise is more noticeable in blue than in magenta and red.
  • the detection axis has therefore been changed to some extent, so that less blue is detected. This improved the general picture quality.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Processing Of Color Television Signals (AREA)
  • Color Image Communication Systems (AREA)

Abstract

Dans un procédé d'amélioration de la finesse, la présence de couleurs prédéterminées (R, M) dans un signal d'image (composante de luminance y à l'entrée, composante de luminance u à l'entrée, composante de luminance v à l'entrée) est déterminée (7) de manière à obtenir un signal de commande (CTRL) et la finesse du signal d'image (composante de luminance y à l'entrée, composante de luminance u à l'entrée, composante de luminance v à l'entrée) est améliorée (1-5) en fonction du signal de commande (CTRL).
EP97940279A 1996-10-21 1997-09-26 Amelioration de la finesse Withdrawn EP0868817A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP97940279A EP0868817A2 (fr) 1996-10-21 1997-09-26 Amelioration de la finesse

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
EP96202924 1996-10-21
EP96202924 1996-10-21
EP97200705 1997-03-10
EP97200705 1997-03-10
PCT/IB1997/001159 WO1998018263A2 (fr) 1996-10-21 1997-09-26 Amelioration de la finesse
EP97940279A EP0868817A2 (fr) 1996-10-21 1997-09-26 Amelioration de la finesse

Publications (1)

Publication Number Publication Date
EP0868817A2 true EP0868817A2 (fr) 1998-10-07

Family

ID=26143264

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97940279A Withdrawn EP0868817A2 (fr) 1996-10-21 1997-09-26 Amelioration de la finesse

Country Status (5)

Country Link
EP (1) EP0868817A2 (fr)
JP (1) JP2000502548A (fr)
KR (1) KR19990076726A (fr)
MY (1) MY130988A (fr)
WO (1) WO1998018263A2 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100780724B1 (ko) * 2001-11-14 2007-11-30 주식회사 엘지이아이 디지털 티브이의 선명도 향상 장치

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5267028A (en) * 1988-08-26 1993-11-30 Canon Kabushiki Kaisha Solid state image pickup apparatus having luminance control
JP2722784B2 (ja) * 1990-06-12 1998-03-09 松下電器産業株式会社 カラー撮像装置
JPH07231396A (ja) * 1993-04-19 1995-08-29 Mitsubishi Electric Corp 画質補正回路

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9818263A2 *

Also Published As

Publication number Publication date
JP2000502548A (ja) 2000-02-29
MY130988A (en) 2007-07-31
WO1998018263A3 (fr) 1998-06-18
WO1998018263A2 (fr) 1998-04-30
KR19990076726A (ko) 1999-10-15

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