Apparatus for digitally scanning colour documents

p0001The invention relates to an apparatus for digital sampling of colored image originals according to the preamble of claim 1.

p0002The presently known devices for digital scanning of image originals operate according to two basic principles. Either the image to be digitized original is illuminated with a white light source, then a color separation, for example by beam parts and color filters, takes place or the lighting has been in the spectral colors red, green and blue instead, the photosensitive sensor may be monochrome. A disadvantage of all known processes is that they have an indirectly proportional to the scanning signal to noise ratio.

p0003To improve the signal / noise ratio are well-known TDI sensors. These have a plurality of rows that are orientated transversely to the movement direction of the original image and their shift clocks are synchronized with the movement. It is clearly displayed and scanned an image strip on the first line. Synchronized to image motion the result of the first line is shifted to the second line and the image strip scanned again and 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.

p0004From the <patcit id="pcit0001" dnum="EP0796005A2"><text>EP 0796005 A2</text></patcit> is an apparatus for digital sampling of colored image originals known comprising at least one photosensitive sensor movable relative to the original image, the movement being synchronized with the scanning, and a light source, the photosensitive sensor is a TDI sensor, wherein the light source is formed such that these adjacent RGB light strips generated, the light strips are transverse to the lines of the TDI sensor. The light source is constructed as a white light source being arranged before the sensor is a suitably structured RGB color filters.

p0005The invention is therefore the technical problem of creating a device for digital scanning of colored image originals by means of which an improved signal / noise ratio with a small number of photosensitive sensors.

p0006For this purpose, the photosensitive sensor is a TDI sensor, wherein the light source is designed such that these adjacent RGB light strips generated, wherein one light strip illuminates one line of the TDI sensor and the color of the light stripe, is synchronized to the shift clocks of the rows of the TDI sensor, can be switched in the order of RGB. This RGB image may be generated by a panchromatic TDI sensor having a much better signal / noise ratio.

p0007In a preferred embodiment, the light source is designed as a LED matrix, by means of which strip-shaped R, G, and B light strip can be produced. Here preferably triple-assemblies each stripe of R, G and B LEDs are alternately driven. Could, however, a static setting of R, G and B stripes, wherein the LED array synchronized to the shift clocks of the TDI line is moved. The advantage of alternately driving the triple arrangement is that no masses must be moved. Preferably a plurality of such triples LEDs along a TDI line as the matrix are arranged.

p0008In an alternative embodiment, the light source is constructed as a white light source with a downstream color LCD matrix, the permeability of the matrix alternately synchronized is switched to the shift clocks of the TDI line.

p0009Preferably takes place after complete scan of all the TDI line nor a phase correction to compensate for local displacements. These shifts occur in that by the movement travels each part of the image already in the adjacent color channel.

p0010Preferably, a lens disposed between the light source and the image original by means of which the light stripes are displayed on the original image.

p0011In a further preferred embodiment, the device is formed with a film stage, the image on the original is moved, wherein the film stage has a slot-shaped light passage.

p0012In a further preferred embodiment a lens is arranged between the film gate and the TDI-sensor, by means of which the illuminated by original image on the TDI sensor or the line is imaged.

p0013The invention is explained in more detail with reference to a preferred embodiment. . In the figures:<dl id="dl0001" 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>

p0014In the <figref idrefs="f0001">Fig. 1</figref> is shown with TDI line 2 schematically shows a TDI sensor. 1 The accumulated charges a TDI line 2 are synchronously intermittently shifted from left to right. Dashed over TDI line 2 are light strips 3 shown. It should be noted that the TDI line 2 can be formed with almost no distance, whereas the light stripes do not necessarily touch, as long as they cover only the respective line. At a time t₀ lies before the drawn distribution of light strips. 3 After a shift clock of the TDI line 2 at the time t₁ there is a about a respective color level-shifted to the right light Stripe distribution. This is the image strip, the beispielswei se the first TDI line 2 at the time t₀ looks, always red illuminated at all times. Clearly, one can say that as an image strip in direction A moves the associated light strip 3 moves together.

p0015In the <figref idrefs="f0002">FIG. 2</figref> is schematically shown the device 10, comprising a white light source 11 with parabolic reflector 12 and a first lens 13 to produce parallel white light 14. The parallel white light 14 incident on an LCD matrix 15, which synchronously by an electronic control unit 16 to the shift clocks of the TDI is sensor 1 is driven, thereby changing the color of a column of the LCD matrix 15 in the order RGB. About another 17 optical light strips are mapped onto a moving towards T template image 18, for example a film. This exposed image section is displayed with different colors illuminated light strip by means of a further optical system 19 on the individual lines of the TDI sensor. 1 It synchronously the light strip is changed by driving the LCD matrix 15 with the shift clocks of the TDI line.

p0016In the <figref idrefs="f0002">Fig. 3</figref> is an alternative embodiment is shown, wherein an LED array 20 is used as a light source that can generate a function of the control electronics alternately R, G and B light strips. In this case, such as in the embodiment of<figref idrefs="f0002">FIG. 2</figref> so many streaks of light as TDI line available are produced which vary spatially along the lines RGB and time according to the pattern in RBG shift clock of the TDI line.