DV’s in-context mastering25 January 2007
In-context mastering, in which clients grant approval to HDTV and mobile video output within the grading suite, may come a step closer if technology developments at Sweden’s Digital Vision bear fruit, writes Adrian Pennington.
In-context or ‘digital multi-format mastering’ is the major R&D focus for the image processing developer and a topic on which it plans to elaborate further at NAB.
“As broadcasters and facilities are required to deliver more and more formats they need a data processing rather than video processing system,” explained company president, Simon Cuff. “We have good technology for producing the best pictures for any given bandwidth, but what’s lacking for d-cinema, mobile, HDTV or HD-DVD applications is an encoding and mastering environment where you can look at the output format in the context it’s going to be delivered.”
Swedish based commercials and film post producer Chimney Pot has researched the idea with Digital Vision claiming that its clients are excited by the idea of having iPods in the grading suite so that approval for iPod video output can be made at the same time as the TV output.
“It’s not as simple as creating a universal master of uncompressed 2k 10-bit or HD 4:4:4 and automatically building deliverables from that,” says Cuff. “The reason that that’s not going to give you best quality is that you’ve already committed to the grade, compression, grain and aperture correction and you can’t unpick from that.”
Each format he says requires its own ‘audition’ or adjustment to aperture correction or vignetting for example to enable different creative looks. “Vignettes behave very differently on a small screen,” adds Cuff. “You want to make sure your eye is drawn to the right bit of action when you’re looking at 2 inch by 1 inch screen.
“Say you’ve graded for cinema and crushed the blacks and whites to create a 10-bit master. You can’t then retrieve that information when it comes to HDTV delivery and you want to lift detail out of the shadows to optimise the image for a lighter environment or digital screen.”
HD DVD and Blu-ray compression involve 4:2:0 sampling which Cuff noted is highly susceptible to noise and information loss when encoding. For films encoded for theatrical distribution using 4:4:4 or wavelet JPEG2000, grain is often desirable.
“It’s reasonable to think that when shooting digital film or HD formats you don’t need grain reduction, but actually on all digital formats you need it more and more. You have to manage grain differently for each format, sometimes subtracting, sometimes adding it back in, so ideally you need grain management before the grade but at the same time ensuring it doesn’t interfere with compression.”
Digital Vision’s solution is to retain the master as a 16-bit or 10-bit log side by side with metadata so users can master to every single format and unpick the settings.
“We’re working on ways of viewing 4:2:0 when in a 16-bit or 10-bit 4:4:4 mastering environment so you can look at an image and recalibrate spacial and pixel resolution to different delivery targets from within the mastering format.”
The firm claims it has customer demand for such technology in HD-DVD and d-cinema as well as its traditional grading markets. “Broadcasters are asking how they can move their archive into online or mobile delivery formats retaining quality in as automated a manner as possible,” he said. “Deliverables are going to be key to the success of the forward thinking facility.”