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The CASIO Exilim camera used in high speed
recording mode
Andrew Davidhazy School of Photo Arts and Sciences/RIT Rochester, NY By way of introduction I'd like to state that this how a fleeting idea possibly becomes the basis for further "research" and a possible solution to a vexing "problem" in high speed photography especially as illustrated by the Casio Exilim camera. It is presented here acknowledging that no research has been done into whether this was something already suggested by someone else in the world.  The Casio Exilim camera is capable of 300 full frame pictures per second. Quite a feat in itself and useful for many applications. But the camera is also touted as being able to record 600 and even 1200 pictures per second.  How does the camera
accomplish this feat? Well, like all high speed cameras do in a manner
of speaking. The camera gives up "spatial" resolution in order to gain
"temporal" resolution. And so what does this mean?It means that if one needs to transfer fewer data points than are required for a full frame of information one can, instead of transferring all the data associated with one frame, concentrate on a new set of data points (a new "frame") and devote 1/2 the time to one image and the other half of the time to the next one. Effectively this doubles the framing "rate". So what does the camera do to go to 600 pictures per second? It simply cuts the frame into 1/2 and this is called now a 1/2 frame aspect ratio camera. The frames are 1/2 as tall as the full frame and they are dealt with in 1/2 the time as a full frame might be. And how about 1200 pictures per second? Well, the frame is cut in half again and the time available for each quarter frame is 1/4 of the time required for the full frame. So 300 x 4 - 1200 pictures per second. This is how most high speed film cameras achieve similar results. Give up frame size to gain framing rate. In these cases one ends up with rather unusual aspect ratios for the recorded frames. Maybe suitable for photographing arrows or similar objects i flight but usually not too practical for more likely scenes that call for an aspect ratio of maybe 3x4 as in traditional TV format. What to do? Here is a suggestion: Place an anamorphic lens in front of the Casio camera's lens at the time it is being used in the high speed, 600 pps mode and make a recording. What is an anamorphic lens? It is one that shrinks the field of view of a an imaging system in one direction but not the other. In is simplest form it is negative cylindrical lens. Most image forming lenses are convex or positive. Anamorphic lenses are cylindrical and negative (usually) in focal length (if I recall correctly). The anamorphic lens, placed in front of the prime lens and oriented in such a manner that it compresses a scene in the vertical dimension while not affecting the horizontal one, shrinks the vertical field of view to fit, let's say, within the confines of the reduced vertical dimension of the sensor (at 600 pps it is 1/2 as tall as it is full frame as stated earlier). After the record is made each image of the stack of images making up the sequence are resized while unconstraining the dimensions of the image. So an image that in its full frame size could be maybe 2000 x 3000 pixels, when used at 600 pps is reduced in size to 1000 x 3000 pixels. Then each image is uncostrained in proportions and the vertical dimension is "amplified" by digital interpolation to twice its vertical dimension. This then makes each frame taken at 600 pps the same size as one that would be made at full resolution and possibly suitable for easier visual examination than one which has an odd aspect ratio, Further, if the anamorphic component shrinks the files size to 1/4 its normal coverage one can envision :full frame" aspect ratio images that have the "look" of a full frame high speed movie made at 1200 pictures per second! IMPORTANT NOTE: You seldom get something for nothing and that is the case here as well. Obviously the system is "interpolating" image data rather than actually capturing "real" data. Can one trust the interpolation? In my opinion it is often quite acceptable to do this. What other price is there to pay? Well, the images will suffer from a certain degree of optical deterioration associated with photographing through an anamorphic lens element. Will the results be acceptable? This is for each individual to determine for themselves. In some cases no but in some cases yes. In closing I should mention that some cameras accomplish similar modification for full-frame recording rates but not by cutting a frame simply in height but the software allows the user to simply select smaller areas within the full sensor to be sampled or used as the basis for each image of the stack. This simply results in a loss of spatial resolution while keeping the aspect ratio of the individual frames at some desired relationship. One might call this "2nd generation" image splitting! There are many ways to solve a problem. Often this involves compromises. This is very evident though out the field of high speed photography. Now to see if someone already suggested this. Somebody probably already has I bet. But for me this was something to think about this evening. |