The effect of a film projector in digital video technology

Good day to all Habravets. Surely, many of you like to go to the cinema, in this amazing and somehow attractive world. Surely, many photographers, videographers, cameramen and editors thought about how to make their final work more interesting and like a movie.

Carried away by photography and video editing, at one fine moment I thought - the resulting picture is too realistic and does not look like a “movie” at all. Having rummaged on the Internet, no solutions to this problem were found, except for the effects of adding all sorts of dust, dashes, hairs and scuffs, like on a film. In addition, watching the latest films in FullHD format, with its very realistic and lively picture, also deprived this cinematic magic. I had to go on an expedition and carry out excavations - a study of the subject area.

Since we are not getting this movie - like magic effect , let's compare our home, digital and analog film projection technologies.

It is definitely clear that the whole thing is the frame rate of the video material. The frequency in a video / movie is the number of frames played per second. The more frames played per second, the more vibrant and realistic the image on the screen. Well, and, accordingly, vice versa, within reasonable limits, because if the frequency, for example, is 1 fps, then this is more like a slideshow.

So what do we have? Digital SLR cameras record video on the order of 30 fps, and (somehow historically) in the cinema this number is 24. “So that's the solution!”, I thought, and ran to remodel my video from 30 to 24 fps . But it was not there! Of course, the difference was noticeable, but it was not like a movie. Even an attempt was made to cut the video into separate and static frames-pictures (so that everything was honest, that everything was like on film - 1 frame and 24 such frames for one second), and gluing them back into the video is not like a movie and that's it here! Digging further.

Now let's take a deeper look at the film projector. Film film projector is a mechanical device in which frames are scrolled, and light from a powerful lamp passing through a film frame and lens system creates an image on the screen. The device, I must say, is very interesting, and, as usual - not very complicated. Feature of the film projector is a shutter device. The obturator blocks the luminous flux during the change of frame when pulling the film to prevent blurry images on the screen. It turns out that the light passes through the positive (film frame) immediately at the moment of its immobility and fixation (positive). What do we have? The frame is fixed - light goes through it, the frame changes - the obturator blocks the light. Usually, a shutter is a disk with slots rotating in front of the projector lamp through which light is transmitted / blocked.

We are trying to put the acquired knowledge into practice. To do this, we cut the video into images again and insert images with darkness between them (that is, the moments when the frame changes and the light is blocked).

It turns out that our "scheme number 1" has the form:1 frame + darkness + 2 frames + darkness + ... and so on. Those. per second, we play 48 separate images.

Result: everything flickers, the overall image is incomprehensible, unpleasant to watch. We continue to dig the subject area further.

It turns out that there is some trick in the cinema. In order to reduce the flickering of the film when changing the frame, a shutter with an additional blade (open + closed sections) is used, such a blade is called blank . As you might have guessed - when the shutter is in the idle zone, the frame change does not occur. This allows you to create a projector flicker frequency of 48 hertz, but play the same 24 frames per second. We put it into practice.

Now our "scheme number 2" has the form:1 frame + darkness + 1 frame + darkness + 2 frames + darkness + 2 frames + darkness + 3 frames + ... and so on. 96 images are played in a second.

Result: Flicker less, the picture can be distinguished, but watching such a video will be very short due to unpleasant flicker. Digging further.

Film projectors have one constant, it is called the obturation coefficient . The obturation coefficient shows the ratio of the duration of the open area of ​​the obturator to the frame change period in the projector. For example, the Soviet film projector 23KPK has an obturation coefficient of 0.57, i.e. during the lifetime of one frame, the duration of its illumination is 57% of the total lifetimeof this frame. In addition, the shape of the shutters can be different: as even, cut sections from the disk from the center in a straight line (as if it looked like a BMW icon), and with all sorts of curved cutouts or slots.

It is also worth noting that the overlap of the light flux with a disk obturator with straight cuts from the center (and indeed any other obturator) does not occur immediately, and not instantly, and not exactly from top to bottom, but in a straight line from the radius of the disk during its rotation. Also, the shutter opens, not immediately, and not exactly from top to bottom. Also, as we know, light has a very high speed (and the speed of opening / closing of the light flux by the shutter compared to the speed of light is negligible), which means that the shutter’s work is completely reflected on the movie screen, although we don’t notice it.

The image output to the monitor also happens frame by frame, with a specific and specific frequency. Of course, creating a simulation of the effect of a film projector in digital technology seems possible when working with images at high frequency. For example (back to our “Scheme No. 2”), playing 400 images for processing only one cycle (1 frame + dark + 1 frame + dark), 120 of which are displayed in a frame, then in 80 images - a neat rendering of a disk shutter simulation - closing and opening the image of the frame, then again 120 pictures show the frame, and close the cycle - 80 images of the shutter to close this frame and open the next frame. And this is only the life cycle of the first frame, as if it were an analog projector. For one second of video, you need to render 9600 of these digital images.

My 4-core PC began to work strangely when playing 250-300 digital images per second. And if you add here another monitor response time (the minimum time for which a pixel changes its brightness), which tends to be different for different models, so that the problem can be solved for most monitors? Solving the problem in a universal way is most likely possible, but most likely not worth it.

Quite an interesting result is the "scheme number 3" of the form:1 frame + 1 frame + darkness + 1 frame + 1 frame + darkness + 2 frame + 2 frame + darkness + 2 frame + 2 frame + darkness. This allowed us to further reduce flicker and increase the brightness of the video stream (and simulate the operation of an instant shutter with a coefficient of 0.66). But at the same time, the number of images played per second began to equal 144. The cinema effect is still far from the effect of its sharpness when changing and noticeable to the eye during perception.

Here it is - the mechanical technology of analog film projection, the effect of which is not so easy to imitate on digital technologies.

Thanks to all. The area is very interesting, like its history, I advise.

Obturator - Wikipedia
Film projector - Wikipedia

Also popular now: