Calibration and validation of motion picture scans

Abstract

There is herein described a method and apparatus for the calibration and validation of motion picture scans.

Claims

1. A method of calibrating digital images or digital video clips representative of images and/or data stored on or with one or more frames of a film comprising: imaging the film using a film scanner to obtain scanned images or video clips; placing a transparent calibration pattern in front of or behind a film so that a portion of the transparent calibration pattern is imaged through perforations in the film to form an imaged calibration pattern, the width of the calibration pattern being less than the width of the perforations running up and down sides of the film so the calibration pattern is imaged through the perforations; and determining scanner exposure variation using the imaged calibration pattern, wherein each digitized image of a frame of the film has at least some calibration pattern visible through one or more perforation; and wherein the calibration pattern remains in the digitized image of every frame of the film.

2. The method of claim 1, wherein the transparent calibration pattern comprises a transparent substrate.

3. The method of claim 1, wherein the transparent calibration pattern comprises a pattern of at least one or more lines extending through perforations on the film.

4. The method of claim 1, wherein the calibration pattern is in the form of lines extending down the sides of the film.

5. The method of claim 1, wherein the calibration pattern is in the form of a series of co-parallel lines with lines extending down the length of the film through the perforations in the film and also extending transversely across the film from one perforation to another.

6. The method of claim 1, wherein the calibration pattern comprises a series of patterns at right-angles to each other.

7. The method of claim 1, wherein the calibration pattern is capable of being viewed by a user to allow calibration of the motion picture scan.

8. The method of claim 1, wherein the calibration pattern allows both high and low intensity patterns to be calibrated.

9. The method of claim 1, wherein the calibration pattern is viewable at multiple positions in an imaging field.

10. The method of claim 1, wherein the calibration pattern constructs a map of intensity variation across a whole sensor.

11. The method of claim 1, wherein the calibration pattern enhances error corrected film images, digitally enhanced images, soundtracks, or a combination thereof.

12. The method of claim 1, wherein the calibration pattern verifies that scanner intensity exposure has been varied and correctly implemented.

13. The method of claim 1, wherein the calibration pattern determines and corrects scanner color bias.

14. A The method of claim 1, wherein when the film is 35 mm and has no soundtrack, a calibration pattern is mounted on both sides of the film so that there is a measurement on both left and right intensities of an imaging field.

15. The method of claim 1, wherein, when the film is 35 mm and has an analogue soundtrack, then the calibration pattern is mounted on the side of the film without soundtrack.

16. The method of claim 1, wherein when the film includes one set of perforations, the calibration pattern is mounted on the side of the film with the perforations.

17. The method of claim 1, wherein, the calibration pattern is removable.

18. The method of claim 1, further comprising the step of providing a low density test pattern, wherein the low density test pattern is provided when the film is faded and exposed at low intensity.

19. The method of claim 1, further comprising the step of providing a high density test pattern, wherein the high density test pattern is provided when the film is faded and exposed at high intensity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a representation of a clear film leader exposed on an uncalibrated scanner according to the prior art;

(3) FIG. 2 is a representation of the same image shown in FIG. 1 where calibration has been applied to the image portion; and

(4) FIG. 3 is a representation of the images with calibration pattern lines extending vertically and horizontally; and

(5) FIG. 4 is an expanded view of part of the image shown in FIG. 3.

BRIEF DESCRIPTION

(6) Generally speaking, the present invention resides in the provision of a method and apparatus for the calibration and validation of motion picture scans.

(7) FIG. 1 is a view of a clear film leader 10 exposed on an uncalibrated scanner. The light intensity is greatest at the center and then drops at the edges. Perforations 12 are located at the edges. It is apparent in FIG. 1 that the light intensities are varying from the top to the bottom, and left to right. However, if a set of intensity filters are applied to render the image in a manner which highlights intensity differences at high and low intensities, then this variation becomes much more readily apparent.

(8) FIG. 2 shows where calibration has been applied to the clear film leader image of FIG. 1. The differences between FIG. 1 and FIG. 2 clearly shows the inherent variations in exposure across the imaging field.

(9) During the scanning of a motion picture film, the perforations 12 are also scanned. As previously described by the current applicant in EP 12795584.7 and U.S. Ser. No. 14/352,053, which are incorporated herein by reference, information may be placed in the perforations. To overcome the calibration problem the present invention proposes the use of a transparent calibration pattern being placed in front of or behind the film 10. FIG. 3 and FIG. 4 are representations of the image in FIG. 1 with the calibration lines of the calibration pattern extending horizontally and vertically. By proceeding in this manner we are able to view the calibration pattern through the gap formed by the perforations 12. Therefore, by measuring the intensities of the calibration pattern, it is possible to measure the intensities at the (typically) eight perforation areas in a 4-perforation motion picture frame. It is then possible to measure intensities of the light to both evaluate intensity variations, and to apply corrections to the scanned image.

(10) For example, it is possible to use only fresh air as the calibration pattern. It has been found that although only fresh air works well for high intensities, we need to also include low density calibration patterns in the form of lines 14, 16 to accurately handle low intensity variations. The lines 14, 16 intersect through the perforations 12 both vertically and horizontally.

(11) It is important to note that if scans are made where the image capture is not synchronised to the scanner advance (as per EP 12795584.7 and U.S. Ser. No. 14/352,053), then the position of the perforations 12 will move from frame to frame. It is therefore possible to see the calibration pattern lines 14, 16 at multiple positions in the imaging field, and it is possible to construct a very accurate map of intensity variation across the whole sensor. It is the purpose of this invention to enable the calibration tables to be dynamically calculated by using the intensities of the test pattern.

(12) Using calibration patterning lines used outside of the image is possible as the increase in scanning resolution makes it possible to scan larger areas, while still having sufficient resolution to capture all the detail of the film.

(13) The calibration patterns can be red/yellow/green lines, but it should be understood that any number and colour of lines may be used.

(14) The calibration pattern as shown in FIGS. 1 to 4 is less than the width of perforations running up and down the sides of the film. This means that the calibration pattern should always be visible through the perforation 12, even when the film 10 moves slightly from side to side as is typical in a drive system that does not use sprockets.

(15) The pattern forming the calibration lines 14, 16 consist of a number of stripes of different density, four are shown but any number may be used. The total width of the four stripes may typically be around 0.5 mm-2 mm or about 1 mm. The optical density of the stripes may typically be in the range from about 0.5 to 4 and preferably about 0.5, 1.0, 2.0 and 3.5. Given that the present invention uses fresh air also, this gives 5 densities to be used to calibrate from which is a further advantage of the present invention.

(16) The test pattern is typically be enclosed in a glass plate (similar to that used for test samples as viewed under a microscope) and is placed underneath a film gate, typically 2-3 mm underneath the film. Given that the scanner has reasonable depth of fieldwhich is important for an archive scanner as older film will not be flatthe density of the pattern will be measurable even though the image of the pattern will not be sharp. Given that the pattern is in a glass plate, any contact with badly warped film will not be harmful to the film. Further, given that the pattern is in a glass plate, it will remain flat to the camera lens so there will be no exposure variations due to movement or loss of tension.

(17) Each digitised image of a camera frame therefore has at least some the calibration pattern visible through one perforation 12 (e.g. 16 mm) or four perforations (e.g. 35 mm). Software can determine the intensity of the (typically four) stripes of the test pattern and therefore compute the exposure applied by the scanner. Through a calibration process, ideal values for these intensities will be known, and using the intensities of each image we can therefore determine the exposure variation of each image. This enables the user to determine whether the exposure applied to each frame was as intended. If the intent was to scan the film 10 at a constant light, then we can use the computed variation to correct minor changes in exposure or to determine that the exposure variation was unacceptable and hence reject the scan. In the case that the exposure variation was intentionalfor example where light and dark sections of film are spliced togetherthe computed variation serves both to validate that the exposure was varied correctly, and to serve as a historical record of what exposure variation was applied. This information can then be used when the reel is viewed so that the user can see the film with or without the exposure variations applied. Where the scanner uses an unsynchronised advance, then the perforations 12 move relative to the vertical axis of the camera frame. This means that a different section of the calibration pattern will be visible with each successive exposure. This means that we will see the exposure applied at a different vertical section of the frame. We can therefore validate that the exposures at each section are the same, and correct for minor differences encountered. Over even a small reel of film, it is likely that the perforations will move fully from top to bottom of the exposure field, which means that we can therefore compute exposure corrections for the full height of the frame.

(18) Since the test pattern will remain in the digitised image of every frame, we will now have a permanent indicator of the exposure used in every scanned image. This means that scans can now be interpreted according to a universal standard. It also means that we can compensate for minor intensity variations during a scan. Further, it allows us to vary scanner intensities to suit content, yet to preserve a record of such variations in a way that means the information cannot be detached from.

(19) Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. For example, any suitable type of calibration patterns may be used.