cinematography

profilechoid
TheCamera-BasicDigitalConcepts.pdf

The Camera FTV 122E: Digital Cinematography

Professor Soraya Sélène

Film (Analog) and Digital

Film (Analog) and Digital

*Film records an image by varying the density of silver or dye of the film emulsion in a continuous gradient from clear to opaque, black to white.

* Digital builds an image with numbers in a binary format. Detail is limited to a scale with discrete numbers of values, determined by the number of bits being used.

Digital Concepts

Digital Concepts

◈ Pixels and Chips ◈ Resolution ◈ Exposure / Dynamic Range ◈ Gamma and Log ◈ Video vs. Data, Raw vs. De-Bayered ◈ Video Scanning – Interlace or

Progressive ◈ Compression ◈ Color Space ◈ ACES ◈ Bit Depth ◈ Color Sampling

Pixels and Chips

◈ PIXEL The PIXEL (“PICture Element”) is the building block of digital image, represents one sample of picture information

Pixels are grouped into fixed arrays of straight rows and columns

Digital Sensor • Analog-to-digital conversion (A/D conversion) – sensor converts light into voltage • Analog voltage is sampled, and converted to digital code value. This determines

brightness. • Color is determined by the chip design in the camera

Pixels and Chips

◈ CHIPS Three-chip design – three 2/3”-size chips, one each for measuring red, green, and blue light

Single-chip design – one large chip, tiny red, green and blue filters over each sensor on the chip in a ”mosaic” pattern

Most widely used mosaic filter pattern is the Bayer pattern

Three Chip Design

Three 2/3”-size chips, one each for measuring red, green, and blue light

Single Chip Design

One large chip, tiny red, green and blue filters over each sensor on the chip in a ”mosaic” pattern

Resolution

◈ The more pixels used to display an image, the finer the detail

◈ Resolution is the measure of the finest detail visible in a displayed image, defined by the number of pixels recorded in the image raster

◈ Camera resolution defined by the number of lines of pixels (scan lines) it records.

HD 1080, or 1920x1080 (columns (pixels per line) x lines)

2K = 2048 pixels per line

4K = 4096 pixels per line

Exposure & Dynamic Range

◈ Film Dynamic range, range of usable f-stops

◈ Film – gradual “rounding off” of values at either end of tonal scale (highlights and shadows), perceived extension of the dynamic range

◈ Digital “clipping”

Gamma: Log/Lin

◈ Film have a logarithmic response to exposure, S curve

◈ Shooting in LOG to emulate the “film look” – approximates a film gamma, resulting in a wider dynamic range and greater shadow detail

Video Scanning – Interlace or Progressive

Compression

◈ Intraframe codec – processes each frame individually, only removing redundant info from within that particular frame

◈ Interframe codec – uses a series of frames, or groups of pictures (GOP), to compress the image data. Interframe compression compares consecutive frames within each GOP to remove redundancy from frame to frame

More efficient, higher compression ratio Can create challenges in editing and postprocessing (due to multiframe dependency)

◈ Compression ratio – compares the amount of data in the original noncompressed signal to the compressed version. The lower the compression ratio, the higher the quality of the image (2:1 vs 4:1 compression)

Color Space

◈ Device-independent vs device-dependent (Film)

◈ Color gamut – range of colors a system can record or display

◈ CIE (Commision Internationale de L’Eclairage) XYZ color space has been industry standard device-independent reference.

◈ Chromacity diagram – represents the full range of human vision. Triangles within this colored shape approximates the gamut of digital cinema

ACES (Academy Color Encoding System)

Bit Depth

◈ Bit depth determines the number of levels available to describe the brightness of a color

1-bit system – only 0 and 1, black and white

8-bit – 256 steps, or numbers from 0-255 (255 shades of gray)

10-bit – 1024 steps, displays more subtle tones (more number of steps assigned to highlight values)

◈ 10-bit log standard for recording digital images back to film.

Color Sampling

Camera Systems and Formats

Sensors and Aspect Ratio