Apparatus for digitally scanning colour documents

0001The invention relates to an apparatus for digital sampling of colored Image templates according to the preamble of claim 1.

0002The presently known devices for digital scanning of image templates operate according to two basic principles. Either the to be digitized Image original illuminated by a white light source, then a Color separation, for example by beam parts and color filters, takes place or the Lighting will take place already in the spectral colors red, green and blue, the photosensitive sensor may be monochrome. A disadvantage of all known The method is that this an indirectly proportional to the scanning speed signal have to noise ratio.

0003To improve the signal / noise ratio are well-known TDI sensors. These have a plurality of rows transverse to the direction of movement of Image template are aligned and their shift clocks with movement are synchronized. It is clearly an image strip on the first line mapped and sampled. Synchronized to image motion is the result of pushed first line to the second line and the image resampled and stripes so on. This allows the signal-to-noise ratio can be greatly improved. However, due to the TDI principle that for colored image templates three separate Sensors must be used. This again is relatively complex.

0004The invention is therefore based on the technical problem, a device for to create digital sampling of colored image originals, by which a improved signal / noise ratio with a small number of photosensitive Sensors.

0005For this purpose, the photosensitive sensor is a TDI sensor, the light source is designed such that these adjacent RGB light strips generates, in each case one strip of light one line of the TDI sensor illuminated and the color of the light stripe, is synchronized to the shift clocks the Lines of the TDI-sensor in the sequence RGB is switchable. In this way, by a panchromatic TDI sensor, an RGB image can be produced, which is a much better signal / noise ratio has.

0006In a preferred embodiment, the light source is designed as a LED matrix, by means of which strip R, G, and B light strips can be produced. there are preferably triple-assemblies each stripe of R, G and B LEDs alternately driven. Could, however, a static setting of R, G, and B stripes, wherein the LED matrix synchronized to the shift clocks the TDI line is moved. The advantage of alternately driving the triple arrangement however, is that no masses must be moved. Preferably A large number of such triples LEDs along a TDI line as matrix arranged.

0007In an alternative embodiment, the light source as a white light source with downstream color LCD matrix formed, the permeability of the matrix alternately synchronized with the shift clocks of the TDI line switched becomes.

0008Preferably made upon completion of scanning of all TDI line yet Phase correction to compensate for spatial shifts. These shifts occur in that already in by the movement of each part of the image the adjacent color channel migrates.

0009Preferably, between the light source and the image template lens arranged by means of which the light stripes are displayed on the original image.

0010In a further preferred embodiment, the device is with a Filmbühne formed, through which the original image can be moved, wherein the film stage having a slit-shaped light transmission.

0011In a further preferred embodiment, between the film carrier and the TDI sensor arranged a lens by which the illumined master image is mapped to the TDI sensor or its rows.

0012In an alternative embodiment of the invention, the photosensitive sensor is as TDI sensor formed, wherein the light source is designed such that this juxtaposed RGB light strips generated to the light stripe transversely the lines of the TDI sensor extend. The advantage of this arrangement is that the Light strips must not be switched. However then need for a adequate geometric resolution the light strips very fine and ideally only a few pixels wide.

0013The invention is described with reference to a preferred embodiment explained in more detail. . In the figures:<dl tsize="6" compact="compact"><dt>Fig. 1</dt><dd>is a partial schematic view of a TDI-sensor,</dd><dt>FIG. 2</dt><dd>a schematic representation of a device with an LCD matrix and</dd><dt>Fig. 3</dt><dd>a schematic representation of a device with LED matrix.</dd></dl>

0014In FIG. 1, a TDI sensor 1 is shown schematically with TDI lines 2. there the accumulated charges of a TDI-line 2 in synchronization cyclically from left shifted to the right. Dashed over TDI line 2 are light strips 3 shown. It should be noted that the TDI line 2 with virtually no spacing may be formed, whereas the light strip not need to touch, as long as they cover only the respective line. At a time t₀ this is the drawn distribution of light strips 3 before. After a shift clock of the TDI line 2 at time T₁ is a about a respective color stage right shifted from light Stripe distribution. This is the image strip, the For example, the first TDI line 2 at the time t₀ looks to keep all Times illuminated in red. Clearly, one can say that as a Filmstrips toward A moves the associated light strip 3 moves together.

0015In FIG. 2, the apparatus 10 is schematically shown comprising a White light source 11 to 12 with parabolic reflector and a first lens 13 Generating parallel white light 14. The parallel white light 14 incident on a LCD matrix 15, which of the synchronous by control electronics 16 to the shift clocks TDI sensor 1 is driven, whereby the color of a column of the LCD matrix 15 changes in the order RGB. About another 17 are the optics Light strip on a moving towards T template image 18, for example, a film ready. This exposed image section with the different colors illuminated light strip by means of a further optical system 19 on the each row of the TDI sensor 1 shown. Here is the synchronous Light strip by driving the LCD matrix 15 with the shift clocks of the TDI line changed.

0016In FIG. 3, an alternative embodiment is shown, wherein as the light source an LED array 20 is used, the function of the control electronics can generate alternating R, G and B light strips. In this case, be as in the Embodiment shown in FIG. 2 as many light strips are like TDI line available generated the spatially along the lines RGB and temporally after the pattern RBG change in the shift clock of the TDI line.