GB2183120A

GB2183120A - A device to convert a presentation of a color image to an electrical signal and vice versa

Info

Publication number: GB2183120A
Application number: GB08625672A
Authority: GB
Inventors: Erland Petterson
Original assignee: Victor Hasselblad AB
Current assignee: Victor Hasselblad AB
Priority date: 1985-10-28
Filing date: 1986-10-27
Publication date: 1987-05-28
Anticipated expiration: 2006-10-27
Also published as: FR2589300A1; DE3636593A1; FR2589300B1; JPS62116066A; SE8505056L; SE8505056D0; SE450803B; GB8625672D0; DE3636593C2; GB2183120B

Abstract

A device for converting a color image into an electrical signal comprises a station for presentation of the image in an image plane, a scanning device (7) with at least one light sensitive element arranged to create an electrical signal which represents the brightness of the image in the scanned region and means for moving the light sensitive element over the image plane in a pattern consisting of a number of scan lines covering the image plane, and means for placing exchangeable color filters (34) in front of the light sensitive element in order to obtain a color separation of the image. Each of the color filters is smaller than the image plane and is of a size adapted to generally cover one or a few of said scan lines. A single color filter may be held in front of the light sensitive element (Fig. 2), for manual replacement for successive scans, or a plate (32) may be provided carrying a plurality of filters, the plate being movable with respect to the light sensitive element.

Description

SPECIFICATION A device to convert a presentation of a color image to an electrical signal and vice versa The present invention is concerned with a device for converting a presentation of a color image to an electrical signal, and vice versa.

When transmitting an image long-distance, the image which is to be transmitted is scanned, picture element by picture element, with a predetermined resolution by means of a device which is able to convert the brightness of the picture elements into a modulated electrical signal. When transmitting and receiving color images, the preferred method is to separate the color image into several colors. By means of color filters, the respective colors are separated from the picture in turn and each is then allowed to produce an electrical signal. The receiver receives the respective signals and is allowed to direct reproduction of each of the predetermined colors in turn, one after the other.

Scanning is consequently accomplished in the same number of steps as the number of colors which have been chosen for separation. This makes possible equipment which, except for the color separation and color reproduction, is not generally more complicated than the apparatus which is required for black/white images. The signal for each color even has the same characteristics as signals for black-white images and one may use the same communication channels, e.g. telephone lines.

Even in contexts other than the long-distance transmission of color images one finds apparatuses for conversion of a representation of a color image into an electric signal. One finds, for example, equipment which very much resembles a transmitter and a receiver for long-distance transmission, but which is used locally in electrotyping or other printed media or as the basis for such. Apparatuses exist which produce electrotypes or stencils using an electric signal which is produced on the basis of an image in an apparatus which can be considered to be a picture transmitter.

One may also create an image signal to obtain a non-permanent image presentation on a display.

Such an image presentation may be used for longdistance transmission or locally for information, for checking, or for editing. As is well known, such image presentation may be obtained using a TVcamera providing a signal to a monitor. For such a signal, however, the capacity of such simple transmission lines as telephone lines is not sufficient and in many cases it is preferable to create and transmit the signal using a low frequency, thereupon recording the signal in a memory. The signal is then converted to a high frequency form and is applied to a monitor. In order to create the transmitted signal an image transmitter designed for the purpose is required.

When separating colors it is common to use different color filters in front of the scanning device, which moves across the picture. The color filters must in such case be of the same size as the picture surface chosen for scanning. This leads to relatively bulky color filters and since they must be manufactured with great precision the cost can become considerable. Furthermore, at every place where there is a non-uniformity in the surface of the color filter, a signal will be produced which yields an incorrect image representation.

An object of the present invention is to provide a compact device for color separation in conjunction with signal creation and reproduction which ieads to lower cost for the color filters than is the case in prior art systems and which to a great extent eliminates the risk of incorrect signals due to nonuniformities in the color filters.

A further object of the invention is to provide a device for color separation which makes possible the creation of a color image signal using a continuous process which can be controlled in different ways to accommodate different intended uses.

In accordance with the present invention, there is provided a device for converting a presentation of color image into an electrical signal and vice versa, comprising a station for presentation of the image in an image plane, a scanning device with at least one light sensitive element arranged to create an electrical signal which represents the brightness of the image in the scanned region, means for moving the element over the image plane in a pattern consisting of a number of scan lines covering the image plane, one or more exchangeable color filters disposed in front of the element in order to obtain a color separation of the image so that a plurality of electrical signals can be formed representing the image, each of which relates to a particular color which is separated from the image by means of the respective color filter, and wherein each of the color filters is essentially smaller than the image plane and is of a size adapted to generally cover one or a few of said scan lines and securing means for the above filters are supported by said element moving means, which is arranged to move the color filters together with the scanning element in constant positional agreement with the successive scan lines produced by the motion of the scanning element.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic, partially broken-away, perspective view of an image transmitter embodying the present invention and which can be used for long-distance transmission of pictures or for creation of an image signal for other purposes such as electro-typing; Fig. 2 shows one example of a scanning device used in the transmitter of Fig. 1; and Fig. 3 shows another example of a scanning device.

The image transmitter of Fig. 1 comprises on and in a casing 1 an illumination device 2, a picture holder 3, which is arranged in accordance with the invention, a mirror 5, an objective 6, a scanning device 7 with a picture window 8 and a row scanner 9 as well as a motor 10, a supporting beam 11 on which the mirror 5, the objective 6 and the scanning device 7 are mounted along with a mirror 12 which is rotatabiy mounted by means of a hinge 13. In addition to the illumination device 2, there are provided on the outside of the casing a projection window 14, a key board 15, an electronics unit 16 and an electronic display 17.

The illumination device 2 is hinged and can be raised. Under it there is a circular opening 18 into which a circular socket4 on the picture holder 3 (see Fig. 1) can be inserted. In addition, the picture holder 3 has a picture window 19 which, when the picture holder with its socket is positioned in the opening 18 and the illumination device 2 is in its lowered position, is placed in the light path from the illumination device 2. The light path continues downwards towards the mirror 5 where it is deflected by means of same through the objective 6 and onwards to the scanning device 7. As is shown in fig. 1 the light path can, however, also be deflected towards the projection window 14 by means of raising the mirror 12.

When using the picture transmitter, the picture, which is inserted in the picture holder 3, is projected by means of light from the illumination device 2 via the mirror 5 and the objective 6 onto the picture window 8 of the scanning device 7. There it is scanned the number of times determined by the color separation by means of the row scanner 9 in order to create an electrical signal. This signal can be transmitted to a receiver or can be used in some other mannerforthe purpose of picture reproduction.

A first, simplified embodiment of the scanning device 7 shown in fig. 1 is shown in larger scale and in more detail in fig. 2.

The row scanner 9 comprises a longitudinally extending body which is movable along guides 20 by means of said motor 10. The motor 10 and the guides 20 are supported in a frame 21 with an opening 22 in which the row scanner 9 can move and which generally represents the picture surface.

The image which is to be scanned consists of a projection within the opening 22 of the true film image 4 in the picture holder 3. The projection is accomplished when light from the illumination device 2 passes via the mirror 5 and through the objective 6, as has been described earlier. The picture is consequently projected in such a way that the focal plane is located in the opening 22 at the level of a row scanning member 23 on the row scanner 9. This row scanning member consists of a row of light sensitive elements which, by means of electronic control, can be caused to emit successive electrical signals along the row of elements, so that a line of the image is scanned. As the row scanner moves on the guides 20 the image is scanned line by line until it has been scanned in its entirety.The result of this is a modulated electrical signal which represents all of the picture elements in the image, the resolution ofwhich is determined by the size and separation of the light sensitive elements along the row scanner 9 and also by the speed with which the row scanner moves in relation to the scanning rate along the row scanner, in other words, by the scan line density.

Each light sensitive element emits a signal, the amplitude of which depends only on the intensity of the incident light on the element, without any indication of color. For technical reasons the sensitivity to the light intensity of different colors will vary and it will also vary in relation to the perception of the human eye of the brightness of the different colors, but these conditions cannot be used to create a signal which also indicates color.

As was mentioned in the introduction one must instead separate the image in different colors using color filters and scan the image successively, color by color. A minimum of three colors is required; all colors and nuances of color can be produced by mixing three colors if these three colors are appropriately placed with respect to each other on the technical color circle. Separation into more than three colors also occurs. In color printing it is common to make a separate printing in black, which corresponds to a black and white signal. Such printing is called four-color printing.

Color filters are used for the color separation and in order not to distort the color perception when the image is viewed in the picture window 14 via the mirror 12 it is preferable to place the color filters near the scanning device 7. According to the invention, each of the color filters consists of a narrow plate 25 which, as is seen in fig. 2, is inserted into mounting strips 26 on the row scanner 9.

The color filter plates 25 will therefore, when they are mounted in order on the row scanner, follow the row scanner during scanning. Each color filter plate only needs to be of the same width as the light sensitive elements in the plane 23, which in principle is only the width of one line. For reasons of handling it is however suitable that the plate should have somewhat greater width. Not only does this facilitate handling, it also requires less precision in the mounting of the plate. The length must of course be the same as the length of the row of light sensitive elements.

The required color filters can be combined in a switching device so that it is not necessary for the filters to be handled separately as is the case with the mounting strips 26 as shown. In this case, one possibility is to provide the color filter plate with several areas, each of which has one of the said colors. By pushing the plate into different positions in the strips 26 the different areas can be placed in front of the row of light sensitive elements.

Alternatively, the switching device can be arranged as, for example, a "revolver" device.

The form of the invention shown in fig. 2 represents the simplest embodiment, wherein the color filters are removed and inserted sequentially by hand. The other said form, containing a switching device, which can be automatic, represents a more highly developed embodiment.

An even more highly developed form is shown in fig. 3 and is to be described below.

As is shown in fig. 3, the scanning device 7 (the designations used in figs. 1 and 2 are also used in fig. 3 for common parts) includes the row scanner 9, which is movable along its guides 20. A second guide means 30 is, however, provided in front of the row scanner 9, i.e., on the side from which the light beam from the projection device incides. On a carriage 31 the guide means 30 supports a plate 32, which stands parallel to the light sensitive elements of the row scanner 9. Inserted into openings 33, the plate 32 supports a number of color filters 34. Seven color filters are shown here. As has been mentioned, a minimum of three filters are necessary in order to obtain the desired color separation.In this case the device has been rendered more universal by providing three filters for the separation of positive images and three for the separation of negative images in addition to which one opening 33 is reserved for the creation of a black and white signal. This is intended for black and white pictures and for black print of four-color printing.

In addition, the device contains a driving device, 35,36 for the carriage 31 so that it can be moved back and forth along the guide means 30. Said guide means 30 should contain a screw 35 which meshes with a thread (not shown) on the carriage 31 and which is driven by means of a second motor 36, which is contained in the driving device.

The driving devices for moving the row scanner 9 along the guides 20 and the color separation carriage 31 with the filters 34 along the guide means 30 are arranged for a specific, coordinated driving sequence. This is accomplished by means of rotational control of the motors 10 and 36. As is well known, electric motors are currently available, usually of the stopping motor type, which can be driven in accordance with complicated rotational patterns, usually under the control of a computer.

Such a motor was available for the present scanning device and must, for the embodiment under discussion, at least be arranged for coordinated control of the two carriage devices. How this can be accomplished is well known to a person skilled in the art and requires no further description here.

The control sequence will, however, be explained herein. Two forms of controlling sequences are possible. In the first form the image is scanned in its entirety in the number of complete sequences which corresponds to the number of colors into which the image is to be separated. In such case the controlling sequence is such that the plate 32 follows the row scanner 9 as it moves over the surface of the image with a particular color filter 34 placed directly in front of and following along with the light sensitive elements of the row scanner during the entire sequence.During the next motion of the row scanner 9 over the surface of the image, in orderto register the next color, the plate 32 is moved in the same manner, together with the row scanner but now displaced, so that the next color filter 34 in turn follows the row scanner, placed directly in front of its light sensitive elements. The resulting signal sequence is consequently divided into a number of sub-sequences, each of which represents the complete representation of the entire image corresponding in turn to one of the different separation colors.

Using the other type of control sequence, the row scanner 9 first scans a single line or, alternatively, a smail group of lines, over the image surface for representation of a color whereby the corresponding color filter 34 is placed directly in front of the row scanner. The color separation plate is thereupon moved so that the next color filter 34 is positioned directly in front of the row scanner 9 which now scans the same line or same group of lines which were scanned earlier for the first color.

In this manner the same picture segment preferably a single lines successively scanned the same number of times as the number of colors into which the picture is to be separated by means of successive movement of the color filters relative to the row scanner.

When all of the colors have been represented the row scanner is moved and scans the next line following the same pattern. The resulting signal will consequently be composed of sub-sequences representing a small segment of the image such as a scanning line. Each subsection is in turn divided into the number of scanning sequences which are required to represent all of the separation colors.

For the latter control sequence the driving devices must consequently be arranged so that the driving deviceforthe row scanner, using the motor 10, maintains the row scanner in the different scanning positions while the driving device for the color separation device, using the motor 36, moves the color filters in front of the row scanner 9 so that all of the intended colors are scanned. Thereafter, the motor 10 moves the row scanner one step and the motor 36 attends to moving the color separation device to a new initial position adjusted to the new position of the row scanner in orderto accomplish a new filter motion for scanning the next color sequence.

As has been mentioned, provision is made for seven different separation possibilities: three color filters for positive images, three color filters for negative images, and the possibility to form a black and white signal. The device for moving the color separation carriage is arranged so as to accommodate the following four different scanning alternatives: 1. Color separation into three colors of a positive color image. In this case the driving device moves the color separation carriage with the three color filters for positive images in turn in front of the row scanner.

2. Color separation for creating three color signals and one black and white signal for a positive color image such as for producing electrotypes for fourcolor printing.

3. Separation into three colors for a negative color image.

4. Separation in four colors for a negative color image.

For the apparatus which has been shown and described the control means for the coordinated motion of the row scanner and the color filter plate must be arranged for switching when a change is made for separation during the abovementioned four different relationships. In case 1, the filters which are intended for color separation of positive images are moved in turn in front of the row scanner; in case 2 the position for the black and white signal is also included in the motion sequence; in case 3 the three color filters for color separation of negative images are moved; and in case 4, in addition to the last named filters, even the position for the creation of the black and white signal is included.

When using the equipment with the scanning device as shown in fig. 2, the starting position of the row scanner 9 is at one edge of the opening 22.

When a suitable image 4 has been chosen and inserted into the picture holder 3, the picture holder is placed under the illumination device 2 and is aligned using the projection window 14 until the desired adjustments have been made. The mirror 12 is then lowered whereupon the image is projected into the opening 22 with the focal plane in the plane 23 of the light sensitive elements.

The order in which the colors are represented in the scanning signal is determined in such a way that image reproduction in the receiver can be accomplished in coordination with the scanning in the transmitter. For the first scan, the filter for the first chosen color is inserted into the strips 26 (fig. 2) and the scanning sequence is carried out. The color filter plate 25 is then exchanged for the next one and the next scan takes place. The sequence is repeated until all of the colors have been represented which, as has been mentioned, will be three or more.

The manner in which the embodiment shown in fig. 3 can be used will have been made clear above by means of the description of the way in which the driving devices for the row scanner and the color separation device are arranged for specific control sequences. Scanning in accordance with the first described control sequence is mainly the same as has been described above for the first embodiment.

The only essential difference is that the exchange device for color filters is shown as being an automatic device for changing the color filters as the picture is scanned in the number of complete sequences which are required for color separation.

At the receiving end, the processing of the signal does not differ from that found in the first embodiment. The entire surface of the picture is consequently built up in several steps whereby the colors are added to one another in turn in order to create the complete color picture.

In the automatic embodiment of the apparatus it can suitably be switched between the different described alternatives for the control sequence and the choice of filters.

Using the other control sequence, with construction of the picture segment by segment with all of the colors represented, another reception method is required. Even for reception it is therefore the case that each segment, preferably a single line, will now be produced individually with the various colors being added in turn in order to create a complete segment. Thereafter, the next segment or line is built up until, after the final segment is reproduced, the image reproduction is completed in the receiver.

The form of the scanning sequence which is chosen also determines which type of receiver one must use. For the first type of scanning sequence a black and white receiver can in principle be used and the addition of color can be accomplished after reception. It is, however, likely that a modified black and white receiver would be used wherein the only essential change would be that the succession of completed signals would be registered using different colors. For registration onto a light sensitive material using a beam of light this can be easily accomplished using a color filter changer. For reception according to the second scanning sequence the receiver must be arranged to follow the same control cycle, which would require greater changes compared to a black and white receiver. On the other hand, this control sequence allows for greater precision in the reproduction.One can easily achieve very good precision in the positioning of the different color representations for the various lines since all of the colors are registered line by line.

Using the first mentioned control sequence, however, one encounters greater difficulties in attaining such agreement of position since the scanning and reproduction devices must be moved synchronously several times over the entire image surface. The last described embodiment as shown in fig. 3, with the last described control sequence, will therefore represent the most highly developed and, for certain applications, the functionally most advantageous technology.

Using the invention, each of the color filters consists simply of a narrow plate, the length of which corresponds to the height of the projected image. Since the color filter plate follows along with the row scanner its light sensitive elements are not moved along the surface of the color filter. Only a narrow central portion of the plate needs to be completely correct with respect to light refraction and color. There is therefore no danger of the row scanner passing soiled portions, which can be the case if a plate which is larger in relation to the fixed plate of the row scanner were to be used in accordance with the method of prior art.

Furthermore, the ability to attain very high precision in the reproduction of images is attained using the most advanced embodiment as shown in fig. 3 along with the last described control sequence.

In addition to the advantages described earlier, the reduction of the size of the surface of the color filter is an additional and equally valuable advantage of the invention.

The form of the invention which is chosen will depend on the demands of the system in which the device of the invention is to be used. If the received signal is to be used to produce printing means such as a number of electrotypes or stencils separated by color, three or four complete and color-separated signals are transmitted. In such case even the simpiest form, with manual changing of the color filter plates, can be used. However, the process goes much more quickly and with less likelihood for error if the automatic device is used. For the case in which a photographic color picture is to be produced directly in the receiving apparatus, precision is increased by better indexing of the color separated images if the second said control sequence is applied with successive construction of the image row by row for all of the colors.In such case the automatic device must be used. This is also the case if a signal is to be created for presentation on a display by means of a memory. On a cathode ray tube type display the colors are built up together so that the last mentioned control sequence is most suitable.

As was mentioned in the introduction, the invention may also be applied to other scanning devices than image transmitters. In such case it is adapted to the intended apparatus and can even have a different construction than the one shown without departing from the scope of the invention.

For example, the row scanner described with a row of light sensitive elements along a scan line could be replaced by a point scanner wherein a scan point is moved along a scan line whereupon it is moved to the next scan line and there carries out the same line scanning. Use of such a methodology does not change the device in accordance with the invention since the color filter could even then be longitudinally extending along a line. In the embodiment of the device for automaticaily exchanging the color filters as shown in fig. 3, two separate driving devices for the row scanner and for the color filters have been described, which drive these members in a coordinated manner according to a predetermined pattern. It is however possible to arrange the device in such a manner that a single driving device is provided but that the color filters are connected with this driving device in such a way that they can be moved relative to it. This means that when scanning is carried out using a particular color filter said filter is fixedly connected to the driving device for the row scanner whereas when the color filter is to be changed, a special changing device effects a relative motion between the mounting device for the color filters and the row scanner. The same scanning patterns can be achieved in this manner as when using separate driving devices.

Claims

1. A device for converting a presentation of a color image into an electrical signal and vice versa, comprising a station for presentation of the image in an image plane, a scanning device with at least one light sensitive element arranged to create an electrical signal which represents the brightness of the image in the scanned region, means for moving the element over the image plane in a pattern consisting of a number of scan lines covering the image plane, one or more exchangeable color filters disposed in front of the element in order to obtain a color separation of the image so that a plurality of electrical signals can be formed representing the image, each of which relates to a particular color which is separated from the image by means of the respective color filter, and wherein each of the color filters is essentially smaller than the image plane and is of a size adapted to generally cover one or a few of said scan lines and securing means for the color filters are supported by said element moving means, which is arranged to move the color filters together with the scanning element in constant positional agreement with the successive scan lines produced by the motion of the scanning element.

2. A device according to claim 1 wherein the securing means for the color filters comprise holder elements, which are arranged on a unit adapted to support the scanning element and are arranged to apply the coior filters in a positional agreement with the scanning element's scan line, which is located within the area of said unit.

3. A device according to claim 2 wherein the securing means for the color filters are arranged to secure a single filter and are arranged for manuai changing of color filters.

4. A device according to claim 1 wherein the securing means for the color filters are arranged to secure a plurality of color filters and to exchange these color filters in turn by moving the securing means relative to the scan line of the scanning element.

5. A device according to claim 4 wherein a control means is provided to displace the paths of motion of the scanning element and the color filter securing means in relation to each other during the scanning procedure in a predetermined pattern so that the color filters, during the scanning procedure, are brought into and in turn are held in positional agreement with the scan lines produced successively over the image plane.

6. A device according to claim 5 wherein the control means is arranged to hold a first color filter in positional agreement with the scan line during a complete scanning of the image for the creation of a first complete color separation signal and, thereafter, to hold the next color filter in positional agreement with the scan line during a complete scanning of the image for creation of the next color separation signal until all of the intended color separation signals have been created.

7. A device according to claim 5 or 6 wherein the control means is arranged to hold a first color filter in positional agreement with the scan line during the scanning of one or a limited number of lines comprising only a limited image segment and to, thereafter, hold the second color filter in positional agreement with the scan line for scanning of the same image segment as in the preceding until all color separation signals for said image segment have been created whereupon the procedure is repeated for a second image segment until all image segments into which the image is divided have been scanned with respect to all of the colors into which the picture is intended to be separated.

8. A device according to claim 5 wherein the scanning element consists of a row scanner which, by means of the moving means, is arranged so as to be moved in its transverse direction over the image plane, and in that the securing means for the color filters comprises a plate with a number of openings into which the color filters are inserted, the plate being arranged to move together with the row scanner and to change its position in relation to same so that the different color filters supported by the plate can be changed and positioned directly in front of the row scanner.

9. A device according to claim 8 wherein the row scanner and the securing means for the color filters each exhibit moving means arranged to move the row scanner and the securing means under the direction of the control means in a manner which is coordinated and which is adapted to the scanning and color separation princess.

10. A device according to claim 8 wherein the row scanner and the securing means for the color filters exhibit common moving means and, in addition, an exchange device for changing the position of the color filters in relation to the row scanner.

11. A device for converting a presentation of a color image into an electrical signal and vice versa, substantially as hereinbefore particularly described with reference to the accompanying drawings, and as illustrated in the accompanying drawings.