Digital Devoid's Blog

Archive for July, 2009

Temporal Resolution

by on Jul.30, 2009, under Image Processing

If a scene changes over time, it is dynamic in the third dimension. The frame rate represents a sequence of images captured over time. The response time of our retinal sensors plays an important role in our perception of motion. Cones and rods use pulse trains to signal the brain, the rate of which is controlled by our exposure to brightness. When the brightness varies faster than the pulse rate, the so called “flicker frequency” is reached. Because the pulse rate of the retinal sensors increases with a greater luminance, so too does the flicker frequency. Beyond the flicker frequency the eye can no longer follow the image changes accurately. This is the frame rate of the eye. Our vision beyond the flicker frequency distorts the field of view creating “alias” temporal frequencies. Our temporal resolution varies from one individual to another, ranging from 10Hz to about 70 Hz and centered around 40 Hz for most of us.

Our temporal frequency response is exposed to frames per second in film and fields per second in video.  (continue reading…)

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Temporal motion interpolation

by on Jul.23, 2009, under Education, Image Processing

Intrinsically, there is a misfit when projecting footage at 24 FPS when the same was captured at 30 FPS. The faster acquisition shutter speed or narrower shutter angle (shorter exposure) of 30 FPS will produce sharper imagery than the desired longer exposure of 24 FPS. In order to simulate opening up the camera shutter angle, applying an appropriate amount of motion blur may be in order. Indeed, some of the “film look” we consider desirable is simply the softness (motion blur) due to the camera’s shutter being open for a longer period of time.

Fortunately, any sophisticated process designed to get from one progressive frame rate to another without “throwing” out frames will provide options to soften imagery by varying degrees. Digital Devoid has developed four distinct methods of motion compensated frame rate interpolation. Each method is available for use through FP Transfer 2K and DP Transfer 4K and is selectively used by us to best resolve imagery when translating from one frame rate to another. (continue reading…)

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Aspect ratio

by on Jul.18, 2009, under Image Processing

One is constantly bombarded by assertions that computers, video and film are incompatible because their respective aspect-ratios are different. This is the myth. The confusion arises because different parts of the concept are conflated. Not only does one need to consider the medium aspect-ratio; one has to consider shape of the pixel, or the pixel aspect-ratio.

Computers and video- and to some degree film- share the same medium aspect-ratio. This is easily verified.  Simply measure the physical size of the computer or video monitor, and you will find that the ratio of the width to the height of the screen is 4 by 3 (1.33:1). An entire cine frame, known as Full Aperture, comprises an aspect-ratio of 1.33:1. Film shot at Full aperture affords a one-to-one correspondence in picture area when transferred to video.

The analogy differs when moving video images to film where the source and target medium aspect-ratios differ. (continue reading…)

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How to optimize tape-to-film transfers

by on Jul.12, 2009, under Image Processing

The diversity of tape to film footage to which Digital Devoid has been exposed enables us to share some hands-on insight with you. We encourage you to review these pre-production notes when planning for a simultaneous film and video release. We are not shying away from problematic transfers; to the contrary, our reputation in the industry is built upon our unique abilities to embrace and resolve the most complex tape to film scenarios through software development.

Scan conversion is primarily concerned with changing the number of lines and fields/frames in a picture sequence. Real-time video standards converters perform satisfactorily in the interlaced video realm where the temporal and spatial distortion is largely disguised by the high refresh rate of the interlaced TV display. However, in progressive scan film projection, these same distortions are immediately apparent. (continue reading…)

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The “beep”, audio 2-pop on film

by on Jul.10, 2009, under Education

We get many questions concerning 2-pop on movie spots. Aside from an audible “beep” heard before the start of picture, what exactly is 2-pop?

To create a release print of a film project two negatives are used, a picture negative and a sound negative. The two negatives are matched up, married, and printed together to create the final release print. A single “beep” frame, called 2-pop, is added to the soundtrack in order to synchronize the sound negative with the picture negative during the printing process.

2-pop is one frame ONLY, of tone, located EXACTLY 2 seconds before the first frame OF PICTURE.

The fact that there are 2 seconds between the 2-pop frame and the first frame of picture seems to create a lot of confusion in some of our clients in the production community. Contrary to what many believe, there are NOT 2 seconds between the 2-pop frame and the start of SOUND. There ARE, however, 2 seconds between 2-pop and the first frame of PICTURE.

This means for example, that if sound is meant to start half a second before picture, then the 2-pop frame will actually occur 1.5 seconds before first frame of sound modulation. If sound is meant to start .5 second into the spot, after picture starts, 2-pop frame will be 2.5 seconds before first frame of modulation.

Leave us a comment if we can help clarify this further!

– Robert

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