The EIZO CG2700X UHD colour accurate monitor

I took delivery of my demo CG2700X Eizo monitor over the weekend and ran it through its paces; suffice to say I am pretty impressed.  

It’s a 27” IPS (so modern LCD) 3820x2160 res panel (so not full-4K) but good for TV, and notably smaller than the 31” FSIs and EIZOs so might fit on a QC desk better than the big guys.

So, first thing is to make a matching profile for the Klein K10A tri-stim probe; I've often written before how a photometer is only as good as the profile you make for it with a spectroradiometer - a CR250 in my case.

Interestingly the spectral power distribution is different from the engineering sample I had half a day with over the summer - Eizo tell me they changed the polariser for production units.

So, for calibration I profiled the display in it's native state (so no gamut imposed by the monitor, all colours as saturated as it will make them).

From that (which is 17^3 - around five thousand colours) I made a rec.709 LUT - 100Cd/m²

Rather splendidly, even though this is a brand new model, ColourSpace was able to talk to the patch generator inside.

It is a single-panel LCD so will not have the dark, inky-blacks you’re used to from a Sony HX-310 or Eizo Prominence (but you could buy a dozen of these displays for the price of one of those!).

In terms of wide-colour-gamut/HDR it has decent emulation for HLG and DolbyVision, topping out at about 550Cd/m² (unlike the full 1,000Cd/m² you expect from an Eizo Prominence or Sony HX-310). So could be used for edit/QC/ingest etc. for those standards, but probably not for final grade/mastering.

first column is 10-bit values, second column is light levels

Cages - still important for broadcast QC types; It has three sets of markers; they can be independently sized and positioned. It has presets for all the common aspect ratios and action/graphics safe areas, but you can set them as you want. You can set all line widths from one to six pixels and choose the colours independently.

I’m not sure if it could be any more flexible?! Aside from circular cages, that is!

My demo unit is safely in a flight case and you guys were on the list for offering it to for assessment; you’re welcome to have it for a few days and I will arrive with it to demo some footage.

Canon's 4k Native IPS television monitors

I had an excellent half day with Canon's UK imaging display guys to look at their DP-V series 4k native displays. To my shame I had assumed that they would be like the HP Dreamcolor or Eizo ColorEdge series monitors which are advertised as being suitable for film and TV work but as I've often said; "..an SDi BNC and a preset called Rec.709 does not a broadcast monitor make"!

In the case of those two manufacturers they assume that taking their print-prep graphics display and making it SDi capable is all that's needed; forget proper RGB linearity and a controlled white-point. In the case of the HP they still advertise it at 250Cd/m² for white (four times what it should be - you can't grade with that) and every time I've had an Eizo to play with I've found the same. Even employing a LUT to tame something like that is a bad idea as having to take 250Cd/m² down to a more sensible 80Cd/m² means you've lost two stops (12dBs, two significant bits) of dynamic range; not what anyone wants.

So - native 4k displays using LED-backlit IPS-LCD and not OLED. Every display technology suffers issues and although I think the poor inherent RGB tracking of OLEDs is entirely addressable in a LUT (which is why I love the Boland BVB25 for colour-accurate TV work) OLEDs are noisy once you get very close to black thus limiting their dynamic range (fine for 10-bit TV work; but for 16-bit HDR film imagery, not so much - yet!). Canon has consequently chosen IPS-style LCDs (with a level-modulated LED backlight). The LED backlight is the same technology as that used in the Dolby PRM-4220 grading monitor which is how they achieve the high dynamic range with a possibility of >1000Cd/m² for specular highlights in HDR 16-bit video. I got to see the originators of this technology, Brightside, back in 2005. 

So, proof of the pudding etc - I profiled the 24" edit suite variant and it was very close to the Rec.709 spec (the fact that I left LightSpace set for a 2.2 gamma whilst the monitor has a true BT.1886 gamma for HD rasters may be to blame). With 4k source material the results look great.

 I started at 2k to see how it did

 At 4k I can only manage 25 FPS at best!

Zooming in on the frequency grating shows aliasing, but only on the camera pics, I couldn't photograph it with my 10Mpix camera without catching aliases in the camera's OTF.

Getting closer gets a bit better, but to the eye the resolution is astounding

 

The Sarnoff ladies at true-4K

 

I profiled the display at 17-points so 5,000 measurements take around two hours with the Klein

 

Looks pretty good for greyscale performance, and I suspect if I set LightSpace's gamma correctly it would be better

The coloured dots are rec.709 and the big cube is the gamut of the display; it covers the colour space nicely.

 

 

The Engineer's Bench podcast - "TV Colour 3 - using LUTs for calibration"

Hugh and Phil go over the practice of using a 3D LUT (look up table) to get OLEDs & LCD televisions closer to the Rec.709 gamut.



Find it on iTunes, vanilla RSS, YouTube or the show notes website.

Using a monitor LUT to try and tame domestic TVs for grading rooms

The venerable old Rec.709 colour space was first proposed in 1990 for HD Television and we still work to it today and the assumption is that pro/broadcast monitors will faithfully translate the Y, Cr, Cb data that comes down a video cable to the R, G, B pixels on the display surface.

For a Sony BVM-series monitor merely doing the following will ensure correct 709 operation;

1. Set the overall black level using PLUGE so that dark areas of the picture are faithfully reproduced.
2. Set the peak-white of the monitor to around 80Cd/m2
3. Check the colour of the white point so that it sits as near to 6504 kelvins as possible
4. Check the 10% grey point for the same colour; track up to peak white and ensure the colour temperature remains constant
5. Check the saturation by putting the monitor into blue-check mode and match the blue coming through the luminance path to the blue coming via the Cb channel.
6. Go back and do it all again as the controls interact somewhat.

However - along with the £18k BVM monitor at the front of the grading suite you also expect a high-end domestic TV for the producer and director to look at and of course they don't want to see any differences! So; here are a couple of monitors we profiled today;

Panasonic TX-50AS500B LED-backlit LCD TV

LG 55EC930V-ZA OLED TV

I used the following to profile these two televisions;

• Klein K10A photometer - my colour probe of choice
• Fuji IS-mini patch generator / LUT
• LightSpaceCMS software to drive the Fuji and read the Klein

Looking at the results would suggest that both displays are almost bang on; in fairness I did try and get them as close as possible using their built in colour-tweaks. The other things to pay attention to is to disable all the dynamic modes; TVs increasingly try and tweak themselves based on picture content or even ambient light and although those things may be great for watching a movie it's hopeless for TV post-production usage. 

It's not just the overall gamut that affects the look of pictures, you have to pay attention to the gamma of the profiles. This is not the same as the 2.2 / 2.4 gamma used between cameras and monitors, rather the relationship between low and high levels for the RGB channels and ideally it should be linear.

LG OLED - although it seems more linear overall it has a strange separation in the blacks.











Panasonic colour gammas - not ideal!  Funny non-linearity in the blacks and poor colour tracking in the mid-tones.









So, once the displays are profiled (it takes around an hour and a half to read the 4900 points that make up a 17-point LUT) you can examine the resulting "cubes" that can be downloaded into the LUT (the Fuji in our case) to make the TV look as close to Rec.709 as possible.

The LG-OLED cube shows that the monitor is capable of displaying almost the entire colour-space but there is a bit of a lump missing from the yellow and the magenta ends. This doesn't mean that those colours aren't available, only that the LUT is having to do the work in transposing the colours in those parts of the gamut with the attendant loss of dynamic range.

Interstingly; that was the first thing the colourist noticed on real pictures "...the magenta in the blacks looks a bit off".

The Panasonic's derived monitor LUT shows a different story; clearly the dynamic range of an LCD is much more modest than the OLED.

To turn the profiles into LUTs you have to use the "convert colour space" in LightSpace. Selection of Peak Luma, or the alternative Peak Chroma, defines the parameters the LUT is generated with - Peak Luma maintains the peak Luminance of white, while Peak Chroma will drop the Luminance if required to prevent colour channel clipping, if the peak Y value of a colour channel is greater than that of whites.

Once converted you can export the LUT in a variety of formats for use in other manufacturer's converters. One nice touch is that if you "select all" LightSpace will write out a folder of LUTs in every format it supports; takes around a minute and means you can hand a USB stick to the customer without any worry of incompatability. 

So - once loaded into the Fuji both TVs were now a darn sight closer to the look of the Sony BVM monitors. The problem is that you're in a dimly lit room with the golden eyes of a highly-paid colourist and it's remarkably difficult to get them to be happy if there are ANY discernible differences. The one chap I was talking to today did finish the conversation with "...still, if you could get a £2k TV to look exactly like an £18k monitor we would never buy £18k monitors!"

Once final point - the client had bought an AJA LUT to use - loading the derived LUT into the AJA looked no different from the Fuji from a colour point of view but it did show banding in the Cr channel - like it is only an 8-bit LUT; I need to chase the further.

Digital path & SDi does not colour-accurate pictures make...

Recent years have seen many prosumer camcorders with HDMI outputs so that you can get access to the uncompressed RGB sensor output rather than having to make do with the H.264 (typically) encoded Y, Cb, Cr data (from the flash or disk-based recorder). This makes lots of sense and has given rise to HDMI -> SDi converters like the ones Mr. Blackmagic sells;

These take any HDMI 1.4 resolution (all the way to 4k UHD - 3840 x 2160 at a maximum of 30P in 4:2:2 colour space) and convert to single-link (1.5G, 3G or BM's home-brewed 6Gbit/sec) SDi. Excellent, you'd think; and they are so long as you only use them for video-type sources - camcorders etc. Don't assume they are of any use in turning the output of your computer into SDi!

So, here's the test rig; my Macbook Pro 15" running Mavericks with a Thunderbolt -> DVI breakout connecting to the HDMI input of the BM converter.

 

The SDi output is fed to my trusty Tektronix WFM7100-series and I'm running a known-good recording of 10-bit, 1080 50i 100% EBU colour bars on the 2nd display.

Now let's take a look at the state of the bars; not pretty - the luminance response is all over the place with a very funky gamma that has really gone awry in the bright parts of the picture. The blue colour-difference channel is not so bad, but the Cr (red colour difference) is really crushed in the cyan end of it's response; look at the vector display (top-left).

That's not to say that the pictures don't look good on the monitor; but they aren't colour accurate in the way they need to be if you're using this as a method of profiling an SDi display - and I have seen people use this method with Light Illusion to derive the colour space of a display and then generate a LUT to make the display look how they want.

So, my first thought was, head over to the display profile and see if it's just using the wrong RGB numbers; OS-X and Windows both support standard profiles like Adobe RGB or sRGB which are more suited to print and web graphics prep but not necessarily our beloved broadcast Rec.709 colour space. Imagine my horror when I realised that the colour display profile that OS-X had used was the one that shipped with the Blackmagic! How did they not even get that right?!

To be fair even the 709 profile that comes with the OS is wrong; the take-away is don't use these kinds of gadgets if you need accurate colourimentry. For XBoxes or just getting a high-quality desktop feed as SDi they are fine, but not if accurate broadcast pictures are needed.

Sony PVM-A250 OLED - some colour measurements

I have a pair of new PVM-A250s in ahead of an install and wanted to test a couple of things out. My first one was to see if the monitor does the right things between it's studio swing-range HD/SDi 4:2:2 input and it's full-range HDMI 4:4:4 inputs. Aside from a slight shift in luma (big Y) the difference is minimal (and definitely not the usual 601/709 matrix-mismatch you see on other monitors).

Y, Cr, Cb 4:2:2 HD/SDi input, peak white field before calibration - out of the box these monitors are a tad blue and a bit too bright.








R, G, B 4:4:4 HMDI input, same source.


We're running these over many hours to see if they drift at all. Will add some more to this post next week with those results.

What's the best setting for Gamma with Rec.709 video?

I've been calibrating TV displays for around twenty-five years and have always leaned on the BBC practice of setting peak white at 80Cd/m2 and the white point at 6504k. For all the decades of standard definition work a gamma of 2.2 has been used. This is required because television cameras don't have a linear transfer characteristic and to make a black-white ramp match (i.e. it looks the same on the monitor as well as to the naked eye) you have to invert the gamma response of the camera at the display end. 

If you get this wrong you wind up with blacks and whites matching but all the shades in between don't - pictures either appear washed-out or all the detail is crushed out of the dark areas of the picture depending on which way you get it wrong.

When Rec.709 came along in the early nineties (for HD television) they changed a few things; new colour primaries, new luminance transfer function, wider gamut etc. They also made a subtle change to the definition of gamma. Like sRGB (the Adobe colour space for graphics working) and Rec.601 the "scene-referred" gamma of 2.2 is specified (in 1992 TV cameras were still tube'd devices) but the display gamma is governed by a complicated transfer law which many people have taken to be closer to a gamma of 2.4. However, a straight power curve of 2.4 is correct only if the display has a zero black level and an infinite contrast ratio, which no real-world display has. The new BT.1886 specification (from 2011) is complex and its precise recommendations vary depending upon the white level, and especially the black level, of the display.

However, if you don't want to bother with a precise BT.1886 calculation a 'best approximation' of this would be a gamma of 2.2 in the low end of the curve rising to a gamma of 2.4 at the high end. In fact it's worse than that - it's linear for the first 10% of the range.

So, what's a colour-calibration guy to do? Once again Charles Poynton comes to the rescue - he's forgotten more things about colour than most of us ever knew and I take his advise whenever possible.

Colors change appearance depending upon absolute luminance, and upon their surroundings. A very dark surround at mastering will “suck” color out of a presentation previously viewed in a light surround. A colorist will dial-in an increase in colorfulness (for example, by increasing chroma gain). The intended appearance for an HD master is obtained through a 2.4-power function, to a display having reference white at 100 Cd/m2 – but that appearance will not be faithfully presented in different conditions! The key point concerning the monitor's gamma is this: What we seek to maintain at presentation is the appearance of the colors at program approval, not necessarily the physical stimuli. If the display and viewing conditions differ from those at mastering, we may need to alter the image data to preserve appearance. In a grading environment, you might set the consumer's display to 100 Cd/m2, matching the approval luminance. However, ambient conditions in an editing environment are somewhat lighter than typically used for mastering today. The lighter conditions cause a modest increase in contrast and colorfulness, beyond that witnessed at content creation.

So, it seems the choice is this - 2.4 gamma in well-controlled grading/mastering conditions (particularly if your monitor has good dynamic range; OLED or Dolby reference monitor) and 2.2 in brighter editing rooms with lower-end LCDs.

Colour results from a Sony PVM-2541 TriMaster OLED monitor

Having spent a bit more time with the Klein K10-A probe I profiled the Sony monitor we hired to practice on.

Here you can see the colour gamut for the displayed compared to the Rec709 colour space for television.

It is an excellent match with the green extremity being a tiny bit mis-matched. I would not expect to see this from either a CRT or LCD monitor.

The white curved line is the "black body locus" and is where physicists define the colour of white.

1. Gamut measurements


White Field
Video  x    y    Y      
255  .313 .336   136.45 

Red Field
Video  x    y    Y      
255  .639 .332   28.35 

Green Field
Video  x    y    Y      
255  .296 .603   99.75 

Blue Field
Video  x    y    Y      
255  .149 .060   9.47 

EBU Overlap Gamut Value:  98.4%

2. Gamma measurements

White Field
Video  x    y    Y      
235  .313 .334   110.99 
207  .313 .334    83.10 
180  .314 .336    58.14 
153  .315 .337    37.74 
125  .317 .338    22.35 
 97  .319 .341    11.39 
 70  .324 .347     3.50 
 43  ---- ----     0.39 
 16  ---- ----     0.01 

Red Field
Video  x    y     Y  
235  .640 .332    24.30 
207  .641 .332    17.79 
180  .642 .332    12.87 
153  .645 .332     7.72 
125  .651 .333     4.20 
 97  .664 .332     1.88 
 70  .671 .325     0.65 
 43  ---- ----     0.09 
 16  ---- ----     0.01 

Green Field
Video  x    y     Y      
235  .296 .603    81.12 
207  .297 .603    57.73 
180  .297 .604    39.60 
153  .297 .604    25.74 
125  .297 .608    14.55 
 97  .297 .614     6.97 
 70  .296 .638     2.27 
 43  ---- ----     0.26 
 16  ---- ----     0.01 

Blue Field
Video  x    y      Y      
235  .149 .060     8.19 
207  .149 .059     5.73 
180  .149 .059     3.89 
153  .148 .058     2.39 
125  .147 .056     1.29 
 97  .143 .053     0.54 
 70  ---- ----     0.18 
 43  ---- ----     0.02 
 16  ---- ----     0.01 

You can see that the colour of white through grey tracks very well until you get to within 15% of black; you can generally accurately read the luminance level down to sub 1Cd/m2 but colour measurements become too noisy down there. The K10-A seems to perform better than our DK PM5639 in this respect.

Some notes on monitor calibration software

Last week I was at a customer's site calibrating monitors and because it was before midday the colourist wasn't there. So - knowing that in the past I'd set the white point on their displays to 80Cd/m2 and 6504k (as per BBC spec!) I balanced them thus.

Later in the day I got a very heated message from the production manager; the colourist wasn't happy and he wanted me back in there to match the Sony BVM to his 55" plasma "...which looks a lot better - much closer to correct". I asked him what standard he wanted the Sony set to and of course he had no idea.

Also - I've had a few people getting very excited about VirtualForge by SpectraCal; it's a test signal generator for a Mac with SDi o/p. The trick is that it talks over the network to their other product CalMan which can talk to the various USB-attached photometers (the XRite etc). They make great play of the fact that this in now a closed-loop where the test patterns can be changed automatically by the probe software. Presumably it still has to tell you what adjustments to make to the display and so how that is any better than you looking at the measurement and make the changes is beyond me.

It makes sense if you have a Sony probe attached to a Sony monitor - the monitor cycles though the various test patterns and reads the probe; it then tweaks the monitor's settings and you hopefully wind up with a properly calibrated displays. Having to have two computers and two bits of software (as well as a network) seems convoluted.

I'll stick with my trustee PM5639s (I have LCD and CRT probes for them) and the occasional hire of a PhotoResearch PR655 when I really need a spectralradiometer over a photometer.

• Test signals for monitor calibration aren't hard - 10% gray, 50% grey, 100% peak white, various saturated colour fields, 100% bars and PLUGE allow you to do anything to a monitor that doesn't need the covers taking off and you getting down to component level.
• Cheap USB photometers that claim to cover different display technologies are plain wrong; LCDs, CRTs, Plasma and OLED all have different metamerisms - a spectralradiometer is the only gadget that is display-technology agnostic.
• Computer monitors and TVs are not grading displays - the MacBook Pro that I'm typing this on is calibrated using Apple's colour tool to D65 but when I point the PM5639 at it the colour temperature is 7340k at 220Cd/m2 (how wrong can it be for grading work?!)
• LUTs can only decrease the dynamic range of a display device - never improve it. The best thing is to get the display calibrated before you start applying LUTs (and then only to simulate the look of a film stock etc).

Colour calibration isn't hard, but it requires understanding the nature of colour and vision and not just spending $395 on a bit of software.

Oh - BTW I carry all my test signals around on a little BlackMagic Hyperdeck. It's battery powered, fits in my rucksack and does proper 709 colour space between it's HD/SDi and HDMI outputs.

Colour calibration probes for less than a grand?

I'm often asked if the kind of colour calibration gadgets you can pick up on Tottenham Court Road are of any use in setting up monitors for film or TV grading – I’ve played around with a couple of those sub-£1k colour probes and although they are OK for getting your monitor in the ballpark for print-prep they aren’t suitable for film and TV usage for the following reasons;

• Luminance level – Computer displays tend to sit white at 200Cd/m2 or even higher so the probe must be able to work over that range. The white level we use in TV is 80Cd/m2 and some film guys prefer 60Cd/m2 (delta-E increases a luminance goes down). This means the probe which (at best) is a ten bit (but probably eight bits) is operating over a fraction of it’s range when used for setting up a monitor for TV grading which means it’s now only a five or six bit probe. There is no way on earth it can measure better than the ½ GND that you need for calibrating for TV & Film.
  
• Metamerism – Photometers (of which this is one) rely on the relative metameristic performance of the display – CRTs are different from LCDs in this respect. That’s why our £5k photometer (Phillips PM5639 in case you’re asked) says on page one of the manual “...only for CRTs, not for LCDs” – I’ve sat a CRT next to an LCD and had quite different colours on both displays and the probe says they’re the same – it’s a limitation of photometers but the Huey claims to be able to do both CRTs and LCDs – not sure how it gets around this as it’s not a calibration issue, it’s physics baby! You need a spectroradiometer to be able to accurately measure both kinds of displays and they start at £15k!
  
• Colour space – computers monitors tend to be set up for RGB working and not for the colour-space we use in TV (rec 709) with a white point at 6500k.
  

So I think these things are worse than useless – they give you a false sense of security for no actual worth.

ITU Rec 601 vs Rec 709 colourspace

Every superhero knows that in transitioning from standard definition television to high def we've adopted a different matrixing function for component to/from RGB conversion. The numbers for (old-skool) Rec 601 are thus;

Y = 0.299R +0.587G +0.114B
Cb = 0.564(B-Y) + 350mV
Cr = 0.713(R-Y) + 350mV

And the new kids on the block (Rec 709);

Y = 0.213R +0.715G +0.072B
Cb = 0.539(B-Y) + 350mV
Cr = 0.635(R-Y) + 350mV

So, not only has the weighting of the colours that make up the luminance path changed but the weighting of the colour difference signals is different. I've heard varying accounts of why they felt the change was necessary - I think it's probably to do with cameras and telecines (now be entirely CCD-based as opposed to the ubiquity of tubes when 601 was being formulated) and display devices (are we going to be able to buy a tube'd monitor by the end of this year?!). The new values better reflect the tri-stimulus nature of human vision and are less bound by the very noisy response of the blue-tube in image acquisition devices of yester-year.

However, one of the upshots of this is that digital devices that can receive an SD/HD-SDi bitstream have to be able to switch in the appropriate matrix. If that isn't the case then you'd notice a green cast on pictures if you switched between standards (going from HD to SD) or a magenta error going the other way. In the case of a monitor you'd have to re-calibrate the white point to D65.

The reason this has cropped up is that a facility (where I've just started to offer them colour calibration advice) has noticed that a monitor that was lined up correctly for HD working is showing the wrong colourimetry when being sent an SD feed. It's gone green (and not with envy! - oh, and that isn't the facility in case you're wondering!). It's a JVC DTV1700 series monitor which (although a cheapie at <£2k) has an EBU-phosphored tube (so you can calibrate it to 6500k at the white point). It looks like JVC's input card doesn't do the matrix switch. So, I'm wondering what other monitors do - I was sure the Sony BVM-D range did (but those monitors started in the mid-teen thousands of pounds). Any comments from people who've hit this before? As an aside the image (right - click it!) is from a very good Tektronix poster entitled Understanding Colors and Gamut - I have many copies (along with the equally exciting Understanding High Definition Video!) - give me a yell if you want one.

"The perils of colour-space conversion" - an article for the Root6 Dr. Watson newsletter

At work we produce a newsletter which I sometimes do a technical piece for - so forgive the slightly client facing tone of this piece!

An important aspect of the production/post-production chain is maintaining correct colourimetry. If the director of photography or the lighting-cameraman want that certain shade of red to be correctly delivered to the viewer then attention needs to be paid to the correct representation from the camera (be it standard or high definition or even film) through all transfer operations (potentially going between resolutions, YUV/RGB colour spaces and bit depths) to the final display surface (be it a CRT, LCD or even cinema screen). In truth colour-space management for film is a complex issue best handled by specialists like Filmlight (who are represented in the UK by Root6) and is perhaps beyond the scope of some technical notes in a newsletter! That said there are many points worth making if you are acquiring or delivering for high definition television and worried about going between colour spaces.

The CIE Chromaticity diagram (first published in 1931!) shows the gamut of human vision – essentially any display surface is a subset of this diagram and will be a triangle with red, green and blue apexes and white (actually monochrome – as the luminance of the image is reduced it tends through grey to black) in the centre. In the case of “illuminant D” (AKA “D6500” or “EBU phosphors”) – the standard definition colour standard used since the sixties in Europe we enjoy a slightly wider red range than our colonial cousins but every gamut (television, film or print) is a poor compromise on what your eyes can handle. This is where the problem begins – you have a very critical instrument at your disposal to see these differences.

Part of the problem is that all of our machines acquire images in the RGB space (TV cameras, Telecines, graphics workstations etc.) but for the most part we post-produce in a YUV space (with the exception of Sony’s new HDCam SR format, an RGB high-definition VTR) which represents an immediate lowering of the colour space. This has been the case for a long time and is well understood. Manufacturers have agreed a common “matrix” for transcoding. To make the luminance portion of the component signal the following is used:

y = 0.299 * r + 0.587 * g + 0.114 * b

Well, this is the case for standard definition (AKA “601”), but for high-def (AKA “709”):

y = 0.213 * r + 0.715 * g + 0.072 * b

Which, even if you’re not so into the maths, will give different values for the luminance (the overall level and hence look of the picture). This makes it doubly important that you get your cameraman to record some colour bars at the head of each rushes tape and that your editor checks alignment on his scope before he starts adding captions etc. The best of breed digital picture instruments are from Tektronics who Root6 are pleased to represent.

If you find you have a colour space issue (particularly going between standard and high definition formats) then the Belle Nuit Montage test chart is a good starting point. It can highlight all the common transcoding errors – be it the limited 8-bit range of old D1 videotape to some of the sub-sampling issues associated with HDCam. You can download the file at various resolutions from their website and by injecting it at the start of your workflow any inadequacies are quickly revealed and can be corrected.