I'm the process of recreating on-screen graphics, and up scaling them, but I have now discovered an issue that needs resolving.
Often when I create a new project and add text, the colour is always set to 235 for each colour. I have now discovered that this the result of Broadcast Safe colouring.
Looking at my reference footage, the colours are all variating with contrasts and finding an a appropriate range to work in is proving difficult, as I tend to use the full colour spectrum, and making an image look flat makes the recreation process a little difficult.
I would like to know, was the rule of Broadcast Safe colouring an important guideline for on-screen graphics 20 years ago, or is this just a new guideline because of LCDs and HDTVs?
16-235 level space for RGB and Luminance and 16-240 level space for Cr and Cb colour difference signals have been around since digital component TV carriage was developed in the early 80s. They are defined in the CCIR/ITU 601 spec for SD and ITU709 spec for HD. The relationship between RGB and YCrCb is different for HD and SD - hence the different specs. (SD Y=0.59G+0.30R+0.11B, but in HD it's different with more G and less R and B in luminance)
In broadcast video systems, black is at 16 and white is at 235. Full level RGB are at 235, zero level RGB are at 0. (Or the 10 or 12 bit equivalents)
However if you are designing on a PC and aren't really broadcasting your content then you are probably as well sticking with 0-255, and any 16-235 content you import from a PC capture solution (or rip from a DVD etc.) should be scaled somewhere in your import path (it may happen automatically)
The reason we have 16-235 not 0-255 for broadcast video stems from the days when digital broadcast kit existed as islands in predominantly analogue systems. Analogue signals were often the sources (and in some, even HD, studios there are still analogue connections - such as analogue triax on LDK HD cameras...) and as such they had all the joyous analogue imperfections of transients and spikes that overshoot white and undershoot black. If our analogue to digital conversion had clipped these transients at 0 and 255 we would have lost some of the analogue signal, and when we converted back to analogue again at the other end we could have had nasty ringing and other artefacts introduced by the process.
We don't really use the term 'Broadcast Safe' to describe video levels (it's more used to describe the graphics safe area that you keep content out of - these days we're 16:9 safe in the UK domestically for most output so in 5% top / 5% bottom and 10% left / 10% right). Levels are usually described as 'Legal'
Legal and legaliser are the terms I come across far more frequently in studio/OBs and general editing. Safe always refers to 'safe areas' in these areas in the UK. Global software releases often use non-UK terminology - often US stuff creeps in.
Is it safe? = Can you see it without any danger of it being cropped (i.e. is it within a graphic safe area?)
Is it legal/Has it been legalised? = Are the colours within the accepted range for broadcast?