HD SDI
Defined by the SMTE S292M standard, the interface provides a bandwidth of up to 1.485Gb/s and can transmit the common HD resolutions and frame rates as a digital component video stream. The interface will transmit Y Cr Cb component coded (using luminance and color difference signals) image data with a 4:2:2 sampling structure and a bit depth of 10 bit (linear).

HD SDI dual link
This implementation is specified in the SMTE S372M standard. By bundling two S292M (HD SDI) links the available bandwidth is doubled. This can be used to increase the bit depth from 10 to 12 bit per pixel and convey RGB data with a 4:4:4 sampling structure, or instead transmit an additional alpha channel for every pixel when a bit depth of 10 bit is used. This applies to YCrCb and RGB coded content alike. The latest generation of HDCam SR VTRs can also use HD SDI dual link to record RGB data with logarithmic coding via the interface.

HSDL
This is a manufacturer driven interconnect standard that will utilize existing S292M/S372M compatible infrastructure (such as HD SDI routers) to transmit RGB coded images with a resolution of up to 2048x1556 and a frame rate of up to 19 frames per second. The resolution and frame rate can be varied up to the saturation point of the total interface bandwidth which is equal to HD SDI dual link.

The bit depth is usually 10 bit per pixel but employs logarithmic coding (As used by the DPX files in SCRATCH) to resolve more gray scale information in the mid-range of the image. Crucially the HSDL signal looks like a conventional HD SDI signal to all equipment in its path, however, equipment and capture cards need to specifically support HSDL to be able to process images conveyed this way. Also, unlike with S292 derived content the digital black level has been moved from value 64 to value 1 thus slightly increasing the dynamic range of HSDL coded images. The interface is mostly used by film scanners and linear hardware based color correction tools.
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Should you be unsure about the requirements or procedures, or require advice, email apl@assimilateinc.com