The MSC Camera.
Depth of Field Enhancement for the Light Microscope.
A Proposal to Digital Camera OEMs.
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Comments on the Ricoh Patent.
The Ricoh patent (US5172236, 1990) derives from a background of earlier patents for automatic focus determination in which the lens is focussed back and forth, and the images falling on a single CCD array are analysed with the object of returning the lens to the position where the amount of detail detected in the image is at a maximum. The Ricoh patent differs from these in that selected images, discarded after analysis by the auto-focus devices, are in the Ricoh description stored in memory and composited together after segmentation to form a single image displaying larger areas of focus. This is substantially equivalent to the segmenting and compositing part of obtaining "enhanced depth of field" images described in the MSC Camera outline.
Essentially the same idea has been in use by the laser confocal scanning microscope people since the early eighties. The LCSM method of image procurement is different (photomultipliers rather than CCD arrays), but the principle of matting together the sharpest parts of an axial series of images to give a single image of apparent large depth of field is in principle the same as Ricoh's patent and the relevant part of the MSC proposal, and underlies the thinking of most if not all compositing software in that it is impossible to matte together images from the same object space unless they share a common axis. Whether the Ricoh method of CCD image acquisition (as compared to the photomultiplier method of the LCSM people) is considered a sufficiently inventive step may prove to be open to argument.
Given that simultaneous acquisition of all of the images to be composited is the essential prerequisite of real-time operation, it is clear that the Ricoh patent as it stands could not become the basis of a real-time enhanced DoF camera. It could only be used to image an object space in which there was no subject movement.
The clearest evidence that the Ricoh inventors are still thinking in terms of sequential focus on a single CCD array is shown in col.2, lines 7-11 and lines 18-20 of the full Ricoh patent.
In col. 3, lines 10-11, they refer to their image pickup portion which "may include a charge coupled device (CCD)". Note the use of the singular. If image multiplexing and the real-time operation which it makes possible had been envisaged by the inventors, plural CCD arrays would have figured in their description at this point.
The patents which have referred to the Ricoh patent in the succeeding ten years have been examined and do not impact on the principles outlined in the MSC proposal.
The Olympus Patent.
This patent includes, as one of the embodiments of a deep-focus camera concept, the use of beamsplitters to replicate the prime image. The relevant parts of this patent, with comments, will be posted in this space at a later date.
In the meantime, those who are interested to read the patent will find it in the records of the US Patent Office under the number:
US5148502: Optical image input/output apparatus for objects having a large focal depth.
Issued/Filed Dates: Sept. 15, 1992/Oct. 9, 1991.