Interlaced to progressive scan image conversion

An image processing apparatus that can convert an interlaced signal generated by the 3-2 or 2-2 pull-down process, to a progressive signal without degrading the quality of the image represented by the interlaced signal, even if the interlaced signal contains an ordinary 60-fields/sec signal. The apparatus has a progressive conversion unit 11. The progressive conversion unit 11 generates an intra-field interpolated signal and an a motion-adaptive interpolated signal to convert an interlaced signal generated by the 3-2 or 2-2 pull-down process and containing an ordinary 60-fields/sec signal, to a progressive signal. The unit 11 then determines, for each pixel, whether the intra-field interpolated signal contains a double-image error. If a double-image error is detected, the unit 11 replaces, for each pixel, the intra-field interpolated signal by the motion-adaptive interpolated signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus and an image processing method, both designed to convert a signal to a progressive signal the signal composed of an interlaced signal generated by the 3-2 pull-down process or the 2-2 pull-down process and an ordinary signal interlaced at the rate of, for example, 60 fields/sec.

This application cams priority of Japanese Patent Application No. 2003-311627, filed on Sep. 3, 2003, the entirety of which is incorporated by reference herein.

2. Description of the Related Art

Standard television signals, such as NTSC signals and high-definition signals, are interlaced signals.FIG. 1Ashows the scanning lines for an interlaced signal.FIG. 1Bdepicts the scanning lines for a progressive signal.FIG. 1Cshows a progressive signal obtained by converting an interlaced signal through scanning-line interpolation. InFIGS. 1A,1B and1C, “o” indicates a scanning line and “x” indicates a scanning line interpolted.

InFIGS. 1A,1B and1C, arrow V represents the vertical direction, while arrow t represents the time axis. As illustrated inFIG. 1A, each frame of the interlaced signal consists of two fields that are dislocated from each other in the time axis and the vertical direction. By contrast, the progressive signal is free of field dislocation as seen fromFIG. 1B. The interlaced signal may have an interlace disturbance, such as line flicker, if it has a frequency component that is prominent in the vertical direction of image. The progressive signal does not have an interlace disturbance.

There is a method of eliminating the interlace disturbance. In the method, any scanning line extracted in the interlace process is interpolated by the surrounding scanning lines, as is illustrated inFIG. 1C. This method is known as “progressive transform” or “double-density transform.”

The scanning-line interpolation performed in the progressive transform is motion-adaptive interpolation. That is, as shown inFIG. 2, the inter-field interpolation is carried out, generating a new scanning line. More precisely, for a still picture, an average value of signals PA and PB representing two field pixels adjacent in the horizontal direction is obtained, generating a signal PQ that resets a new pixel x. For a moving picture, on the other hand, the intra-field interpolation is carried out, generating a new scanning line. An average value of signals PC and PD representing two field pixels adjacent in the vertical direction is obtained, generating the signal PQ that represents the new pixel x. If the image is a still picture, the progressive transform can provide an image that has little folding distortion and high resolution. If the image is a moving picture, however, the progressive transform results in an image that has a conspicuous folding distortion and very low resolution.

Assume that the input signal that should be subjected to the progressive transform may be an interlaced signal generated by the 3-2 pull-down process or the 2-2 pull-down process. Then, a method other than the motion-adaptive interpolation may be used. In this case, the progressive transform can provide a high-quality image even if the image moves. Note that the 3-2 pull-down process is a frame-rate conversion shown inFIG. 3. This process is used as a method of converting progressive signals A, B, C, . . . , such as 24-frames/sec film data, to interlaced signals a, a′, a, b′, b, c′, c, c′, . . . of 60-fields/sec, NTSC scheme. InFIG. 3, the prime (′) shows whether the signal pertains to an even-numbered field or an odd-numbered field. Also note at the 2-2 pull-down process is such a frame-rate conversion as illustrated inFIG. 4. The 2-2 pull-down process is employed as a method of converting progressive signals A, B, C, . . . , such as 30 frames/sec film data, to interlaced signals a, a′, b, b′, c, c′, . . . of 60-fields/sec, NTSC scheme.

As seen fromFIG. 3, the original image, i.e., one-frame image, is divided into two or three fields in the 3-2 pull-down process. As can be understood fromFIG. 4, the original image, i.e., one me image, is divided into two fields in the 2-2 pull-down process. Thus, if the 3-2 or 2-2 pattern of the input signal acquired by the 3-2 or 2-2 pull-down process is known, the input signal can be converted to a progressive signal in the 3-2 or 2-2 pull-down process, by performing intra-field interpolation on only the adjacent fields generated from one and the same frame. This can be accomplished no matter whether the image is a still picture or a moving picture. The intra-field interpolation is a process that is different from the inter-field interpolation shown inFIG. 2. Nonetheless, it is similar in that the signal PA for the preceding field or the signal PB for the following field is used as signal PQ that represents a new pixel, thereby to generate a new scanning line. The intra-field interpolation can, therefore, provide images that have little folding distortion and high resolution.

An ordinary 60-fields/sec signal may be inserted by edition into an interlaced signal generated by the 3-2 pull-down process or 2-2 pull-down process. Such an interlaced signal tat contains a 60-fields/sec signal to a progressive signal cannot be converted to an optimal progressive signal by means of intra-field interpolation. This is inevitable because in the ordinary 60-fields/sec signal no field generated from an image exists between two adjacent fields generated from the same image, particularly when the ordinary 60-fields/sec signal represents a moving picture. Consequently, this interlaced signal represents, but a low-quality image. Assume that an interlaced signal obtained by the 2-2 pull-down process and containing a 60-fields/sec signal representing a round object is converted to a progressive signal, as is illustrated inFIG. 5. Also assume that the intra-field interpolation has been performed in the 2-2 pull-down process. Then, the resultant image will include two identical images of the round object, which overlap each other, simply because the ordinary 60-fields/sec signal represents a moving picture of the round object. Obviously, the image is much degraded in quality.

This problem may be solved by the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2000-78535. This technique is to convert a signal into a desirable progressive signal even if the signal consists of an interlaced signal obtained by the 3-2 or 2-2 pull-down process and an ordinary 60-fields/sec signal, without degrading the quality of image. In the technique, one of three signals, which has the smallest absolute value is selected and used as a motion signal K. The three signals are: (i) a succeeding intra-field interpolated signal that is a scanning-line signal identical with the interpolated scanning line for the field succeeding the field of interest in time; (ii) a preceding intra-field interpolated signal that is a scanning-line signal identical with the interpolated scanning line for the field preceding the field of interest in time; and (iii) an inter-frame matching signal that represents the absolute value of the difference between the succeeding intra-field interpolated signal and the preceding intra-field interpolated signal. The motion signal K is applied to obtain an optimal signal. More specifically, the mixing ratio between an intra-field interpolated signal and an intra-field interpolated signal for the field of interest is changed in accordance with the motion signal K. The “intra-field interpolated signal” is composed of the succeeding intra-field interpolated signal and the preceding intra-field interpolated signal. The “intra-field interpolated signal for the field of interest” has been generated by adding the two scanning lines above and below the interpolated scanning line for the field of interest, respectively.

In the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2000-78535, the pixel data items of different fields, i.e., pixel data items acquired at different times, are compared. Any pixel data item pertaining to a moving image inserted therefore changes in value with time. Hence, the intra-field interpolation is predominant. In consequence, any image part other than the inserted image part which can be converted into a desirable progressive signal without degrading the image quality, will inevitably be degraded in quality.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing. An object of the invention is to provide an image processing apparatus and an image processing method that can convert an interlaced signal generated by the 3-2 pull-down process, the 2-2 pull-down process, or the like, to a progressive signal without degrading the quality of the image represented by the interlaced signal, even if the interlaced signal contains an ordinary 60-fields/sec signal. In other words, the apparatus and method can convert both the 60-fields/sec signal and the rest of the interpolated signal to a progressive signal, without degrading the image quality. Note that the interlaced signal has its frame rate adjusted by re-arranging the original-image frames (e.g., frames of film) in a prescribed sequence.

To achieve the object, an image processing apparatus according to this invention is designed to convert an interlaced signal to a progressive signal, the interlaced signal containing a signal converted to have the same frame rate as an image signal that consists of original-image frames arranged in a prescribed sequence. The apparatus comprises: a signal-generating means for performing intra-field interpolation to generate a progressive, intra-field interpolated signal from a scanning line that follows the present field in time and is located at the same position as the interpolated scanning line of the present field, or from a scanning line preceding the present field in time and is located at the same position as the interpolated scanning line of the present field; and a double-image detecting means for determining, for each pixel, whether the pixel of interest, which is contained in the intra-field interpolated signal, is one of pixels that constitute the double image part of the intra-field interpolated signal.

In this image processing apparatus, when the double-image detecting means determines that the pixel of interest constitutes the double-image part, the intra-field interpolated signal generated by the signal-generating means and corresponding to the pixel of interest is replaced by a predetermined converted signal that corresponds to the pixel of interest.

The image processing apparatus may further comprise an interpolated-signal generating means for performing intra-field interpolation to generate a progressive, interpolated signal from scanning lines located above and below the interpolated scanning line in the present field, or performing inter-field interpolation to generate the signal from a scaling line that follows the present field in time and is located at the same position as the interpolated scanning line of the present field, and a scanning line preceding the present field in time and is located at the same position as the interpolated scanning line of the present field. In this case, when the double detecting means determines that the pixel of interest constitutes the double-image part, the pixel of interest, contained in the intra-field interpolated signal, is replaced by a pixel in the interpolated signal and assuming the same position as the pixel of interest.

To attain the object specified above, an image processing method according to this invention is designed to convert an interlaced signal to a progressive signal, the interlaced signal containing a signal converted to have the same fame rate as an image signal that consists of original-image frames arranged in a prescribed sequence. The method comprises: a step of performing intra-field interpolation to generate a progressive, intra-field interpolated signal from a scanning line that follows the present field in time and is located at the same position as the interpolated scanning line of the present field, or from a scanning line preceding the present field in time and is located at the same position as the interpolated scanning line of the present field, and a double-image detecting step of determining, for each pixel whether the pixel of interest which is contained in the intra-field interpolated signal, is one of pixels that constitute the double-image part of the intra-field interpolated signal.

In the image processing method, the intra-field interpolated signal generated in the step of performing intra-field interpolation and corresponding to the pixel of interest may be replaced by a predetermined converted signal responding to the pixel of interest when it is determined, in the double-image detecting step, that the pixel of interest constitutes the double-image part.

The image processing method may further comprise a step of generating a progressive, interpolated signal by performing intra-field interpolation from scanning lines located above and below the interpolated scanning line in the present field, or by performing inter-field interpolation from a scanning line that follows the present field in time and is located at the same position as the interpolated scanning line of the present field, and a scanning line preceding the present field in time and is located at the same position as the interpolated scanning line of the present field. In this case, when it is determined, in the double-image detecting step, that the pixel of interest constitutes the double-image part the pixel of interest contained in the intra-field interpolated signal is replaced by a pixel contained in the interpolated signal and assuming the same position as the pixel of interest.

In the image processing apparatus and method described above, a double image, if any in an intra-field interpolated signal, is detected for each pixel in order to convert the interlaced signal generated by the 3-2 pull-down process, the 2-2 pull-down process, or the like, and containing an ordinary 60-fields/sec interlaced signal, to a progressive intra-field interpolated signal by means of intra-field interpolation. If a double-image is detected, the pixel constituting the double image is replaced by the corresponding pixel contained in another signal generated by means of, for example, motions-adaptive interpolation.

The image processing apparatus and method according to the present invention can perform intra-field interpolation thereby converting a mixed signal consisting of an interlaced signal generated by the 3-2 pull-down process, the 2-2 pull-down process, or the like and an ordinary 60-fields/sec interlaced signal to a progressive intra-field interpolated signal. The apparatus and method can reliably distinguish, for each pixel, the interlaced signal and the ordinary 60-fields/sec interlaced signal from each other. If the intra-field interpolated signal contains a double-image park any pixel that constitutes the double-image part is replaced by the corresponding pixel contained in another signal generated by means of, for example, motions-adaptive interpolation. Thus, both the interlaced signal and the ordinary 60-fields/sec interlaced signal can be converted to a progressive signal, without degrading the quality of image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in detail, with reference to the accompanying drawings. This embodiment is an image processing apparatus and an image processing method. The apparatus and method can convert an interlaced signal to a progressive signal without degrading the image quality, even if the interlaced signal has been generated by the 3-2 pull-down process or the 2-2 pull-down process and contains an ordinary 60-fields/sec signal. In other words, the apparatus and method can convert both the 60-fields/sec signal and the rest of the interlaced signal to a desirable progressive signal.

The image processing apparatus100according to this embodiment is configured as shown inFIG. 6. AsFIG. 6shows, the apparatus100comprises a front image processing unit10, a progressive conversion unit11, a display-driving circuit12, and a display13.

The front image processing unit10receives an image signal from various signal sources. The image signal is, for example, an NTSC signal a PAL signal an HDTV signal from a BS digital tuner, or the like. In terms of signal format, the image signal is an interlaced signal such as a 525i (525-line) signal, a 625i signal or an 1125i signal.

The progressive conversion unit11is designed to convert a 525i signal to a 525p signal (i.e., a 525-line progressive signal), a 625i signal to a 625p signal, and a 1125i signal to a 1125p signal. The unit11can convert an interlaced signal to a progressive signal, without degrading the image quality, even if the interlaced signal has been generated by the 3-2 or 2-2 pull-down process and contains an ordinary 60-fields/sec signal. That is, the unit11can convert both the 60-fields/sec signal and the remaining part of the interlaced signal, causing no image-quality degradation. The progressive conversion unit11supplies the progressive signal, thus obtained, to display diving circuit12.

The display-driving circuit12drives the display13. Driven by the display-driving circuit12, the display13displays the image represented by the progressive signal supplied from the progressive conversion unit11. The display13can be selected from various types of displays such as a cathode-ray tube, a liquid crystal display and a plasma display.

The display-driving circuit12may include a resolution-converting circuit that converts a standard- or low-resolution image to a high-resolution image containing a high-band component that is not contained in the standard- or low-resolution image. Such a resolution-converting circuit is disclosed in, for example, Japanese Patent Application Laid-Open Publication Nos. 7-193789 and 11-55630.

The progressive conversion unit11may have the structure illustrated inFIG. 7. As shown inFIG. 7, the interlaced signal supplied from the front image processing unit10is input, as a present signal, to some components of the progressive conversion unit11. The progressive conversion unit11has field-delaying devices20and21. The field-delaying device20delays the present signal by one field time, thus converting the present signal to a past-1signal. The past-1signal is supplied to the field-delaying device21. This field-delaying device21delays the past-1signal by one field time, generating a past-2signal.

The progressive conversion unit11further has a motion-detecting unit22, a memory23, an interpolated-signal generating unit24of motion-adaptive type, a pull-down detecting unit25, an interpolated-signal selecting unit26, a double-speed conversion unit27, and a pull-down-error detecting unit28. The motion-detecting unit22compares the past-1signal with the past-2signal, detecting a motion if any. That is, the unit22uses the history of motion, which is stored in the memory23and which indicates whether the pixel of interest has moved or not. The motion-detecting unit22supplies the result of motion detection to the interpolated-signal generating unit24. In accordance with the result of motion detection, the interpolated-signal generating unit24performs inter-field interpolation or intra-field interpolation, generating a progressive, motion-adaptive interpolated signal. To be more specific, if the image remains still, not moving at all, the unit24caries out inter-field interpolation in which a new pixel is generated from the average value of any two pixels adjacent in the horizontal direction, thereby generating a new scanning line. If the image is moving, the unit24performs intra-field interpolation in which a new pixel is generated from the average value of any two pixels adjacent in the vertical direction, generating a new scanning line. Thus, the interpolated-signal generating unit24generates a motion adaptive interpolated signal, which is supplied to the interpolated-signal selecting unit26and the pull-down-error detecting unit28.

The pull-down detecting unit25detects a 3-2 pull-down process or a 2-2 pull-down process from the present signal, past-1signal and past-2signal. More precisely, if the input signal is a signal that has been interlaced by the 3-2 pull-down process or the 2-2 pull-down process, a field adjacent to any field must be one that has been generated from the same frame of image. Hence, the unit25can detect either the 3-2 pull-down process or the 2-2 pull-down process, by determining whether the fields have moved with resect to one another. In other words, the unit25correlates the fields, thus detecting a sequence of fields. The signal interlaced by means of the 3-2 or 2-2 pull-down process may contain an ordinary signal. Such an interlaced signal can be used, only if it is determined whether the signal has a value equal or greater than a preset threshold value and it is thereby determined whether the fields are correlated. The pull-down detecting unit25generates a pull-down detection signal that represents the result of detecting the pull-down process. This signal is supplied to the interpolated-signal selecting unit26and the pull-down-error detecting unit28.

The interpolated-signal selecting unit26determines which kind of an interpolated signal should be supplied to the double-speed conversion unit27, from the motion-adaptive interpolated signal, the present signal, the past-2signal and the pull-down detection signal. The input signal may be one that has been interlaced by the 3-2 pull-down process or 2-2 pull-down process. In this case, there must be an adjacent field that has been generated from the same frame of image. Therefore, the interpolated-signal selecting unit26selects and supplies the signal representing this adjacent field (i.e., the present signal or the past-2signal), as an interpolated signal, to the double-speed conversion unit27. The input may not be one that has been interlaced by the 3-2 pull-down process or 2-2 pull-down process. If this is the case, the unit26selects and supplies the signal representing the output signal of the interpolated-signal generating unit24, as an interpolated signal, to the double-speed conversion unit27. The double-speed conversion unit27alternately reads the interpolated signal and the past-1signal at a rate twice as high as the speed of reading the input signal, thus generating a progressive intra-field interpolated signal. The progressive intra-field interpolated signal is supplied to the pull-down-error detecting unit28.

Note that the conventional progressive conversion unit supplies an intra-field interpolated signal to a display-driving circuit, without processing the intra-field interpolated signal at all. The image signal input to the conventional progressive conversion unit may be an interlaced signal that has been generated by the 3-2 or 2-2 pull-down process and that contains a 60-fields/sec signal. If so, the 60-fields/sec signal will inevitably resent two identical images that overlap each other. This would greatly degrade the image quality.

To avoid this, the progressive conversion unit11shown inFIG. 7has the pull-down-error detecting unit28that is connected to the output of the double-speed conversion unit27. The pull-down-error detecting unit28evaluates the progressive intra-field interpolated signal input to it. If the unit28detects a double-image error, it replaces the intra-field interpolated signal with a motion-adaptive interpolated signal. The unit28evaluates the intra-field interpolated signal, for every pixel, in order to detect errors made in the pull-down process. Hence, upon detecting a double-image error, the pull-down-error detecting unit28replaces the intra-field interpolated signal with a motion-adaptive interpolated signal in units of pixels. A double image is detected if the pull-down detecting unit25determines that the input signal is a signal interlaced by the 3-2 or 2-2 pull-down process and if the interpolated-signal selecting unit26uses the present signal or the past-2 signal as a pixel that is to be interpolated.

The pull-down-error detecting unit28may be configured as is illustrated inFIG. 8. The pull-down-error detecting unit28receives a filed-interpolated signal supplied from the doubles conversion unit27. In the unit28, a line-delaying device30delays the field interpolated signal by one-line time. The field-interpolated signal is further delayed by three other line-delaying devices31,32and33, by one-line time in each of these line-delaying devices. As a result, signals A, B, C and D are output from the line-delaying devices33,32,31and30, restively. The signal supplied from the double-speed conversion unit27is used as signal E. These signals A to E have the position relation depicted inFIG. 9. InFIG. 9, the broken lines indicate scanning lines that have been generated by means of intra-field interpolation, and the solid lines indicate the scanning lines for the signal input to the pull-down-error detecting unit28.

For any interlaced signal generated by the 3-2 or 2-2 pull-down process, the lines that lie adjacent to one another in the horizontal direction pertain to the same frame of image. These lines must therefore be greatly correlated. For any 60-fields/sec signal, the lines that lie adjacent to one another in the vertical direction (i.e., lines pertaining to a progressive field-interpolated signal) must be much correlated. Utilizing this fact, the pull-down-error detecting unit28(FIG. 8) distinguishes a signal interlaced by the 3-2 or 2-2 pull-down process from a 60-fields/sec signal.

AsFIG. 8shows, the pull-down-error detecting unit28has absolute-difference calculating units34to37, a one-line, absolute difference average calculating unit38, flip-flop (FF) circuits39to42, an average pixel-value calculating unit43, and a double-image detecting unit53. Each of the absolute-difference calculating units34to37is configured to find the absolute difference between the pixel data items for two adjacent lines. More correctly, the absolute-difference calculating unit34calculates the absolute difference between signals A and B. The absolute-difference calculating unit35calculates the absolute difference between signals B and C. The absolute-difference calculating unit36calculates the absolute difference between signals C and D. The absolute-difference calculating unit37calculates the absolute difference between signals D and E. The one-line, absolute-difference average calculating unit38finds the average of the absolute differences the calculating units34to37have calculated. The average value found by the unit38is supplied to the FF circuit39. The FF circuits39to42supply the average value of the absolute differences for five adjacent pixels, to the average pixel-value calculating unit43. The unit43finds the average value for five adjacent pixels. The average value calculated by the unit43is supplied to the double-image detecting unit53.

AsFIG. 8shows, too, the pull-down-error detecting unit28has absolute-difference calculating units44to46, a two-line, absolute-difference average calculating unit47, flip-flop (FF) circuits48to51, an average pixel-value calculating unit52. Each of the absolute difference calculating units44to46is configured to find the absolute difference between the pixel data items for one line and the line following the next. More correctly, the absolute-difference calculating unit44calculates the absolute difference between signals A and C. The absolute-difference calculating unit45calculates the absolute-difference between signals B and D. The absolute-difference calculating unit46calculates the absolute difference between signals C and E. The two-line, absolute-difference average calculating unit47finds the average of the absolute differences the calculating units44to46have calculated. The average value found by the unit47is supplied to the FF circuit48. The FF circuits48to51supply the average value of the absolute differs for five adjacent pixels, to the average pixel-value calculating unit52. The unit52finds the average value for five adjacent pixels. The average value calculated by the unit52is supplied to the double-image detecting unit53.

The double-image detecting unit53compares the average value supplied from the average pixel-value calculating unit43with the average value supplied from the average pixel-value calculating unit52. The average value supplied from the unit52may be smaller than that supplied from the unit43. This means that the correlation between any line and the line following the next is more prominent than the correlation between any two adjacent lines. In this case, the unit53determines that two identical image, overlapping each other, have been generated. The unit53generates a double-image signal that indicates his decision. The double-image signal is supplied to the output-selecting unit55that is incorporated in the pull-down-error detecting unit28.

The pull-down-error detecting unit28has a two-line delaying device54. The two-line delaying device54receives a motion-adaptive interpolated signal from the interpolated-signal generating unit24and delays this signal by two-line time. The motion-adaptive interpolated signal thus delayed by two-line time by the two-line delaying device54, is supplied to the output-selecting unit55. The unit55receives not only the motion-adaptive interpolated signal, but also the double-image signal from the double-image detecting unit53, a pull-down detection signal from the pull-down detecting unit25and a signal C from the line-delaying devices31. When the unit55receives the double-image signal from the double-image detecting unit53, it replaces the pixels represented by the signal C (intra-field interpolated signal), with the pixels represented by the motion-adaptive interpolated signal and located at the same positions, thereby preventing a double-image error.

A pull-down-error detecting unit28that may be provided in the progressive conversion unit11ofFIG. 7, in place of the circuit shown inFIG. 8, will be described with reference toFIG. 10. As in the detecting unit ofFIG. 8, a line-delaying device60delays, by one-line time, the intra-field interpolated signal supplied from the double-speed conversion unit27. The signal thus delayed is further delayed by line-delaying devices61,62and63, by one-line time in each line-delaying device. Thus, signals A, B, C, D and E are obtained.

AsFIG. 10depicts, this pull-down-error detecting28comprises an average-value calculating unit64, a binary-data generating unit65, a double image detecting unit66, flip-flop circuits67to70, an integrated double-image detecting unit71, a two-line delaying device72, and an output-selecting unit73. The average-value calculating unit64finds the average of the signals A, B, C, D and E. The binary-data generating unit65converts the signals A, B, C, D and E to binary signals A′, B′, C′, D′ and E′, respectively. More precisely, it generates “1” if the pixel data is greater than the average value of the signals A, B, C, D and E, and “0” if the pixel data is smaller than the average value of the signals A, B, C, D and E. The double-image detecting unit66determines that a double-image error has occurred, if a binary-value pattern for five lines is identical to a prescribed pattern.

FIG. 11illustrates a binary-value pattern for five lines. The binary-value pattern may be “1,0,1,0,1” or “0,1,0,1,0” either shown inFIG. 11. This means that the any line and the line following the next are more correlated than any two adjacent lines are correlate. In this case, double-image detecting unit66determines that a double-image error has occurred. The unit66therefore supplies a signal showing the result of decision, to the flip flop (FF) circuit67and to the integrated double-image detecting unit71, too. The FF circuits67to70supply four decision-result signals for the adjacent pixels to the integrated double image detecting unit71. Thus, five decision-result signals for five adjacent pixels are supplied to the integrated double-image detecting unit71. From the five decision-result signals, the unit71determines whether a double-image error has occurred indeed. The integrated double-image detecting unit71determines that a double-image error has occurred if, for example, the binary-value pattern of five adjacent pixels is identical to the pattern of the above-mentioned double image.

The motion-adaptive interpolated signal, thus delayed by the two-line delaying device72by two-line time, is supplied to the output-selecting unit73. The unit73receives not only the motion-adaptive interpolated signal, but also the double-image signal from the integrated double-image detecting unit71, a pull-down detection signal from the pull-down detecting unit25and a signal C from the line-delaying device31. When the output-selecting unit73receives the double-image signal from the integrated double-image detecting unit71, it replaces the pixels represented by the signal C (intra-field interpolated signal), with the pixels represented by the motion-adaptive interpolated signal and located at the same positions, thereby preventing a double image error.

As described above, the progressive conversion unit11of this embodiment converts the input signal, i.e., interlaced signal generated by the 3-2 or 2-2 pull-down process and containing an ordinary 60-fields/sec signal to a progressive signal. To convert the input signal to a progressive signal, the unit11generates an intra-field interpolated signal and a motion-adaptive interpolated signal and determines whether the intra-field interpolated signal has a double-image error in units of pixels. If a double-image error is detected, the intra-field interpolated signal is replaced by the motion-adaptive interpolated signal, for each pixel. Thus, the progressive conversion unit11eliminates the double-image error that would greatly degrade the image quality. Hence, the unit11can convert both the ordinary 60-fields/sec signal and the remaining part of the input signal into a progressive signal without degrading the image quality.

The present invention is not limited to the embodiment described above. Various changes and modifications can be made, without departing from the scope and spirit of the invention.

The above-described embodiment uses the data about five adjacent scanning lines and the data about five pixels adjacent in the horizontal direction, in order to detect a double-image error. Instead, the data about any other number of adjacent scanning lines and the data about any other number of pixels adjacent in the horizontal direction can be used for the same purpose.

In the embodiment described above, the fame rate is 60 fields per second. Nevertheless, this invention can be applied to signals of any other formats, such as a PAL signal that has the frame rate of 50 fields per second.

Moreover, this invention can be applied not only to signals generated by the 3-2 pull-down process and 2-2 pull-down process, but also to signals the frame rate of which has been changed by arranging the frames of the original image in a specific sequence.

As described above, the intra-field interpolated signal is replaced by the motion-adaptive interpolated signal when the pull-down detecting unit25detects a double-image error. Instead, the intra-field interpolated signal may be replaced by any other kind of a signal in the present invention. For example, the intra-field interpolated signal can be replaced by another intra-field interpolated signal.

As has been described, an intra-field interpolated signal or a motion-adaptive interpolated signal can be selected for each pixel in the present invention. This renders it possible to convert an interlaced signal generated by the 3-2 or 2-2 pull-down process and containing, for example, an ordinary 60-fields/sec signal, to a progressive signal, without degrading the image quality. In other words, the invention can convert both the 60-fields/sec signal and the rest of the interpolated signal to a progressive signal, without degrading the image quality.