PLEASE DO ADJUST YOUR SET
By: Mick Peaker
Excerpt from article written for Sound+Image magazine, April/May 2013 issue.
Have you bought yourself a new TV recently? Managed to negotiate the in-store friendly bright smiles and even friendlier and brighter advertisement banners? Most likely you picked the TV you liked the look of best, that best suited your bank balance and - being a Sound+Image reader – which got a good review. Hopefully it looks good now you’ve got it home. (Most likely anything would after that old box you’ve been watching.)
Can you make it look even better? Of course you can. But can you make it truly accurate? Probably not - even if you know your way around the TV’s menus and the Brightness, Contrast, Sharpness and Colour settings. Even once you settle on your settings and end the whole process expressing complete satisfaction, chances are that your TV’s image will remain pretty distant from the ideal. Yet that’s where most people stop.
"Yeah…that’ll do! Let’s watch a movie".
THE COLOURFUL TRUTH
So if “that’ll do”, why get a TV calibrated?
Well, here’s the thing. The human brain has an amazing ability to tune itself to whatever audio or visual information the senses are receiving and to accept that as ‘normal’.
The concept may be more familiar in audio terms. Say your best mate has just bought a stonking new hi-fi system. You jump in the car to go and have a listen, and on your way you’re rocking out to the car audio system – a bit of AC/DC, Foo Fighters, maybe even some Zeppelin. You’re not consciously thinking about it, but it’s sounding great. When you settle down at your mates place, he may hit you a little hard with the first few minutes of music, but soon you’re listening to everything from Simon & Garfunkel to Pink Floyd, Dave Matthews to the latest Muse, immersing yourself in the ambience of every kick and snare hit, every little detail to be heard.
When it’s time to go home, you get back in the car, start the engine and…wait a minute…the in-car system now sounds distinctly below par. That’s because your brain has retuned itself while you were listening to your mate’s new system. It now has a new benchmark of what it accepts as good. But don’t worry too much – by the time you get home your brain will probably have tuned itself back again.
It’s much the same with a TV picture. It’s not until we watch a picture that has been properly calibrated that we realize what we’ve been missing. For the vast majority of viewers, overly bright, oversaturated images have become accepted as the norm.
In terms of colour, it’s worth considering that what you are watching is, effectively, somebody’s artwork. When Leonardo da Vinci painted the Mona Lisa, for example, there were certain colours on his palette, and he chose these colours carefully. This is not unlike what a movie director does when he builds the colours and detail into a movie. The available colour gamut is his paint palette. Although there are a number of different colour gamut's, the standard used for today’s HDTV and the Blu-ray content is ITU-R Recommendation BT.709, or ‘Rec.709’ for short. You can be sure that the movie director’s screens were perfectly calibrated to Rec.709.
Now, if an artist wanted to accurately recreate the Mona Lisa, he would need to use the same colours that were available on de Vinci’s palette. Likewise, if your TV is not calibrated to Rec.709, you’re not going to see the same colour and other nuances that the director intended us to see. It is not fidelity, not true to the source. If Leonardo were to see his masterpiece with a fluorescent green background and orange skin tones, chances are he’d get quite grumpy.
Note that some TVs offer a Wide Gamut option – they can display colours outside of the Rec.709 colour space. The wide Gamut can be useful for photographers or graphic designers, who may use a larger colour space, such as Adobe wide gamut RGB, for their work. But it’s not for the movies – it’s simply the wrong palette.
ABOVE LEFT: Rec.709 colour space, as used for Blu-ray and DVD releases. ABOVE RIGHT: Example of Wide-gamut colour space
OUT OF THE BOX
If calibration is so important, then, why aren’t televisions calibrated correctly when you take them out of the box? There are a number of reasons. One is that the cost of properly calibrating each individual screen at a manufacturing level is just not economically viable. Besides, the lighting conditions of the room affect the final outcome of what we see. This needs to be taken into consideration when calibrating a TV – so out-of-the-box perfection just isn’t possible.
Equally relevant is the extremely competitive TV market; Manufacturers want to catch your attention in that brightly lit shop showroom. The infamous ‘store mode’ – unnaturally bright and colourful – used to be the out-of-the-box default for many TVs and is the biggest reason that TVs look different in the store… they’re all wrong!
The calibration process does depend partly on your TV. Check its “Advanced” or “Expert” settings and look for something about White Balance/Greyscale and Colour Management. If your TV has these, there is a good chance it can be very closely, if not precisely, calibrated to Rec.709. Some TVs only offer White Balance/Greyscale controls. Even those alone can get us 90% of the way home.
CALIBRATION: DYNAMIC range
There are a number of variables to consider while calibrating, but the big three are dynamic range, greyscale and CMS. Dynamic range measures how black the blacks are and how white the whites.
The potential dynamic range will vary depending in the quality of the screen, but essentially we’re looking to get the picture as black as possible without losing detail in the dark areas of the picture, and as white as possible without losing detail in the bright areas of the picture.
A pattern, similar to the image below, is used for setting the dynamic range – this is called a ‘pluge’ pattern (Picture Line-Up Generation Equipment). The number 16 marks the reference point for ‘black’ and 235 marks the reference point for ‘white’.
With this pattern, we want to adjust the Brightness up or down until we can just see the bar below 16. If we adjust the Brightness too low, the blacks will be ‘crushed’ and we will lose essential detail in the dark areas of our picture.
Then we want to adjust the Contrast up or down until we can just distinguish the bar above 235. If we adjust the Contrast too high, the whites will be ‘clipped’ and we will lose essential detail in the bright areas of our picture.
Greyscale is how the TV produces the colour grey, from black through to white. This is what gives us light and shade: the black and white detail of the picture. An even gradient from black to white is produced when the primary colours Red, Green and Blue are evenly balanced.
This is where the White Balance controls come into play. Many quality modern TVs will have a two-point High/Low control for each primary colour – ‘High’ for the lighter half of the greyscale, and ‘Low’ for the darker half. Some TVs have a 10-point control in which red, green and blue can be adjusted at 10 individual points, from black to white, along the grayscale, allowing for greater accuracy in adjusting the RGB balance. The image below represents pre and post-greyscale calibration of a Samsung 8000 LED TV (my calibration using a SpectralCal CalMAN 5).
Pre and post Greyscale calibration of Samsung 8000 LED
CMS (Colour Management System) is where we adjust the red, green and blue primary colours and the cyan, magenta and yellow secondary colours. The approach that each manufacturer takes with their CMS controls will vary, but essentially they all adjust x and y co-ordinates and the luminance for each colour to match the Rec.709 colour space.
The images below shows pre- and post-CMS calibration of a Samsung 8000 LED TV.
ALL TOGETHER NOW
Dynamic range, Greyscale and CMS all relate to each other. If one is altered they can all be affected. So during the calibration process it is essential to revisit each step in the process and make adjustments until they are all balanced.
And further, each component in a home cinema system – receiver, video sources – has the potential to alter the video signal. So once the display is properly calibrated, we need to check the signal at each component in the signal path, back to the source, making adjustments along the way if necessary.
The benefits of correct professional adjustment all though the chain can be significant.
Professional calibration can potentially deliver the following benefits and more:
- a sharper, clearer picture;
- detail reveled that was previously missing from the picture;
- realistic colours and flesh tones;
- increase the life of your display;
- decrease the likelihood of ‘phosphor burn’;
- decrease the power consumption of your display.