One of the main reasons for the expansion in DI workflows, not just for feature film work, but for generic post-production, is the ability for DI systems to be almost totally agnostic when it comes to the input image format.

However, some systems are more agnostic than others, and it is here that things can, and do, go wrong, and is one of the main reason's I have thus far favoured the Quantel iQ Pablo and SGO Mistiak for DI work - they are genuinely image format agnostic!

Image format issues can come in a variety of shapes and sizes - literally - with different resolutions, different bit depths, different file formats, different frame rates, interlaced/progressive, etc. However, most such issues are readily understood, and even if the DI system of choice is not able to automatically work with the various differences, the differences tend to be so obvious that the operator can take steps to manually correct the problem.

However, there is an image issue that has been largely ignored as its effects can be hard to spot initially, until the very end of the process chain, when the problem becomes all to obvious.

The problem stems from the merging of traditional video images with IT or date centric images, but has nothing to do with the 'physical' attributes of the image, as listed above as resolution, bit depth, etc...

The problem is with the setting of an image's black and white point for display.

The above diagram graphically illustrates the problem, although as the central DI system is shown as an iQ Pablo the problem is actually dealt with automatically, but it's the only system I have found, to date, that does understand and deal with the issue!

To help understand what the problem is, imagine you are working with Dual Link HD in RGB 4:4:4, but through equipment limitations are monitoring via single link HDSDI output in YUV 4:2:2. The input signal has black & white points set to 4-1019, while the monitoring signal has black & white set to 64-940, which means the signal you are working with to do the grading is not showing the full image detail.

On top of this the monitor will have been setup using a PLUGE signal to set its display black to 64, so even if the monitor signal can be set to allow over range information, the monitor will still not show it.

After this potential issue has been resolved, there then comes the different needs of the various deliverable formats - Single Link HD, Dual Link HD, DPX data files, SD Video, all of which expect different black & white points...

A lot of fun and games that have been overlooked in many systems and setups.