| US4484073A | 1984-11-20 | |||
| US4876452A | 1989-10-24 | |||
| US4527060A | 1985-07-02 | |||
| US4916316A | 1990-04-10 | |||
| US4571493A | 1986-02-18 | |||
| US4767927A | 1988-08-30 | |||
| US4582988A | 1986-04-15 |
| 1. | A method for reading an image sheet containing stored image information with stimulating radiation, whereby the stimulating beam is made to scan the sheet line by line, and the light which is generated by the stimulating beam and emitted from the image sheet is measured and converted to correspond to the image information, c h a r a c t e r i z e d in that the scanning beam is interrupted at a certain frequency, and the emitting light is correspondingly measured periodically in synchronization with the scanning, and whereby the interruption frequency is essentially higher than the line frequency. |
| 2. | A method according to Claim 1, c h a r a c t e r i z e d in that the length of the turn off cycle of the scanning beam is so dimensioned that a significant part of the afterglow of the light emission caused by the previous effective cycle of the stimulating beam has time to fade out during the turnoff cycle. |
| 3. | A method according to Claim 1 or 2, c h a r a c t e r i z e d in that the oncycle and the turnoff cycle of the stimulating beam are approximately equally long. |
| 4. | A method according to any of the preceding Claims, c h a r a c t e r i z e d in that the emitting light is received, and measured at least once also during the turn off cycle. |
| 5. | A method according to any of the preceding Claims, c h a r a c t e r i z e d in that the scanning beam is turned off at least 100 times, for instance, approximately 1000 times during one line. |
5 The object of the present invention is to provide a method for reading visual information stored on an image sheet t with a stimulating beam, whereby the stimulating beam is made to scan the sheet line by line and the light generated by the stimulating beam and emitting from the image sheet 10 is measured and converted into a signal which corresponds to visual information.
Such a method is particularly used in connection with X-ray photography for reading so-called RIM plates (radiation 15 image plates) . Such a method and device is disclosed, for instance in U.S. patent 4,527,060.
The reading of the RIM plate is carried out in such a way that a very small laser point is conducted on the surface
20 of the RIM plate, and the radiation thus generated is collected by a light-conducting member in a light multiplier, the signal from which is further processed to obtain visual information. The laser beam is made to scan the surface of the RIM plate by using a turnable mirror
25 controlled by a galvanometer. The mirror moves the laser point in a reciprocating movement across the RIM plate, while the plate is moved in a linear direction.
The luminescent substances on the RIM plate comprise an 30 after-glow property which impairs image contrasts, however, particularly with respect to the image points subsequent to the highly irradiated spots.
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The purpose of the following invention is to reduce this r 35 drawback and thus simultaneously improve the contrasts of the image being read. In order to obtain this object, the invention is characterized by that which is disclosed in appended Claim 1.
An essential feature of the invention is thus that the stimulating beam, generally a laser beam, is interrupted ' at a certain frequency and the light emitting from the RIM plate is measured and analyzed in synchronization with the interrupting of the stimulating beam. The light is always measured while the laser beam is on, and also is preferably measured at least once between the image points, that is, while the laser beam is off.
In this connection, it should be mentioned that it is known in the art that the laser beam is always turned off for the time of .the return trace, in a manner similar to the reception of a television signal. However, this interruption naturally does not eliminate the problem mentioned above, which is caused by after-glow.
In the following, the invention is described in more detail in an exemplary manner and with reference to the accompanying drawing in which: Fig. 1 represents schematically the device for the reading of the RIM plate, and
Fig 2. represents the functions related to the description of the method according to the invention.
Reference number 1 of Fig. 1 denotes the laser source which emits laser beam L via turnable mirror 2 to RIM plate 3 which is to be read.
The light emitting from the surface of the RIM plate is collected by light-conducting member 5 and guided via filter 6 to light multiplier 7, from which the signal is taken to processor 8 of the system.
According to the invention, laser beam L is interrupted in the control of processor 8 at a certain frequency, for instance, approximately 1000 times per each line or the turning cycle of mirror 2. Galvanometer 10 which turns mirror 2 as well as the linearly moving carrier 4 of RIM plate 3, is controlled by processor 8.
The digital information formed by processor 8 which corresponds to the visual information of RIM plate 3, is transferred to memory 9 where it can be further outputted in a suitable manner.
It is obvious that the system can further comprise other parts, such as amplifiers, additional optical members, etc., which have been omitted from figure 1, however, since they are not essential from the point of view of the invention.
The image contents with respect to one line are represented in principle in Fig. 2, point a. Point b represents the state of laser beam L; that is, the beam is switched on and off several hundred times during one line.
Point c represents a measured signal or a signal of light multiplier 7, when the signal is always measured once per the state of the laser beam, that is, once while the laser beam is on and once while the laser beam is off. Point d represents, respectively, the signal of light multiplier 7 when two measurements are taken per each state of the laser beam.
The portion of after-glow in the signal coming to the light multiplier can be compensated by subtracting the portion of after-glow of the previous image points from the signal which is measured while the laser is on, the latter portion of which can in turn be determined by the signal which is measured while the laser is off. Because the after-glow is gradually attenuated, the accuracy of compensation naturally improves as the number of measurements during each state of the laser beam is increased.