Colourimetry, Rec.709 and HDR video; a presentation.

A couple of weeks ago I was up in Glasgow doing a presentation at Root6 Scotland's PlatformOne event. Gerry shot some video so here it is (in case it's useful). 

The PDF of the notes is here, the URL of the YouTube clips is https://youtu.be/sFpDE8fKlco

The damage 100m of good-quality coax does to a 1080i signal.

I've posted measurements of the degredation that cables does to video signals before; see here, but I was grabbing a couple of screen caps for an industry colleague and here they are.

Boland's new hi-brite 7" camera/on-set monitor

It seems to be a thing for small on-set/camera monitors that they should have a hi-bright mode when being used in non-edit environments. The Boland BVB7a is an excellent little monitor and can be powered from the camera's 12v battery feed as well as coming with a DC PSU. It can take SDi (single or dual-link) as well as HDMI and composite (yes!). I shot a little video of me profiling it's colour capabilities.

BM UHD/4k converters - some gotchas

https://www.blackmagicdesign.com/products/miniconverters/techspecs/W-CONM-17

I've used a few of these guys recently - Blackmagic's quad HD/SDi input to HDMI 2.0 output for taking the UHD / 4k (either tile or 2SI standard) and making something that will display on a 4k domestic TV.

They seem to work quite well, but here are a few things that I had to get around;

1. Firmware - I had two identical ones and I initially tested both with Quad-SDi out of Avids at UHD (3840x2160 at 25 & 30P) - all good. But when I started a 4k project (4096x2160 at 24P) only one worked - the other showed nothing on it's HDMI output. Eventually discovered only one of them had current (v.7 as of May 2016) firmware!
2. Power cycle if colour space wrong - both have periodically decided they are going to mistranslate Y, Cb, Cr -> R, G, B - power cycling fixing it; hopefully the next firmware update will stop this?
3. Four signals are always interpreted as UHD; if the Avid is running an HD project the four SDi feeds out of the back are all identical and the converter has no way of knowing it's not quad-link. The Tektronix 8200-series and the Canon VP3010 monitor both have to be told (and I set presets for just this) but the BM converter needs to see three or fewer signals to realise it's only a 1920x1080 raster. In the case of this job setting up two macros on the video router (one to route all four, one to send a non-used input to i/p's B, C, & D of the BM).
4. Glad I'm rocking a MacBook Pro! I would not have been able to update the firmware otherwise as I've yet to move on from Windows 7 - and the workshop PC is still 32-bit Windows 7!

The Engineer's Bench Podcast - tops tips for video

Next in our tips series - broadcast video.
Go to the website for a PDF of the notes.

https://youtu.be/18QR4E1yzKI



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

Tech Breakfast – “Encryption”, Soho Screening rooms, London

A presentation I gave; starting with the fundamentals of cryptography (difference between symmetric and public-key etc), I talked about encryption techniques used in the Enigma machine (with a genuine, working example) through to HDCP and the other forms of content protection used in our industry: 

• Symmetric vs Public-key crypto 
• Examples – DES, AES/Rijndael etc 
• HDCP, Blueray and the MPAA etc 
• PCoIP – security of KVM extenders 

Notes are here
http://www.engineersbench.com/phil/Public/Root6-misc/TechBreakFast_March2016_Crypto.pdf

Crypto - March 2016 Root6 Tech Breakfast notes & Ross Anderson

You can grab my notes here, event details http://www.root6.com/news/tech-breakfast-encryption/

Also - good watching on YouTube:

A review of Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography by Michael S. Tooms

All of my colourimetry comes from doing it; my theoretical knowledge isn't that great as I didn't study it at university and the colour training at the Beeb, although entirely appropriate to what a TV engineer needs was just that; TV-centric.

Over the last ten years I would credit the following industry colleagues for widening my understanding and appreciation of colour reproduction;

1. Martin Euredjian of eCinema Systems was a colourist and telecine engineer before he started making reference-grade LCD monitors - Root6 sold them for a while (around a decade ago) and Martin was very generous in his product training. He opened my eyes to the problems of metameristic failure between different display technologies.
2. Martin Parsons of Image Eyes who used to be the head of colour at MPC; like me he's now a colour-gun-for-hire but I always enjoy getting his take on things and since he 's done an awful lot of calibration he knows when it's appropriate to maybe go slightly off standard to match two displays and keep the colourist happy.
3. Steve Shaw is the proprietor of LightIllusion where I have bought probes, LUT boxes and of course LightSpaceCMS which really is the best calibration package out there. In terms of speed and accuracy nothing comes close.  Steve is very gracious with his knowledge and runs a good forum on his website as well as being a prolific presence on Lift, Gamma, Gain.

I recently was recommended Michael S. Toon's book Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography.  I picked this up at Amazon to read on the iPad Kindle app and like most academic volumes it comes in around sixty quid.

So - as mentioned, my background is the CIE1931 chromaticity chart and how that then relates to Rec.601, 709, the DCI-P3 colour space and Rec.2020 (the proposed colour space for UHD TV which is as yet no available on any current-model monitor).

Any practical skills I have with colour come from;

1. Calibrating and matching TV cameras ("racking" or "shading" in the USA) for studio shoots.
2. Calibrating and matching TV monitors - firstly in tape edit suites (it was always common practise to have two grade-1 monitors; the record monitor and the preview monitor).

So I think I have a good eye for quickly spotting how two displays differ - I can match two monitors or cameras pretty quickly but like most people I don't have perfect colour memory (and don't let any colourists tell you that they do!).

The first things the book set me straight on was the history of colour research before the CIE1931 diagram. Before cinematography and early colour TV experiments the concerns of industrial colour science was mixing of paints and pigments. An important consideration in colour mixing is being able to predict new colours from the volumetric mix of two pigments and the early colour models (Munsell and Guild & Wright) tried to reflect this with a choice of primaries at 460, 530 and 650nm giving rise to constant lines of "just noticeable difference" - JND - on their chromaticity charts.

However - the negative lobes associated with the gamma (green) and rho (red) responses mean that an all-encompassing colour chart should place the primaries outside the spectral-locus which gives rise to non-consistent lines of JND and a grey-scale definition in video colour spaces that seems to be at odds with the equal-energy point in the centre of the CIE1931 chart that gives us our white mix.

one of the worksheets that are available for download with all the empirical data used in the book tabulated and plotted

So I have no hesitation about recommending this book; it is readable and has enough maths so that you never think there is an slight-of-hand going on. For me it has filled in the holes that bothered me in my knowledge of colourimetry. If all the changes that are going on currently in the industry (principally Rec.2020 and the XYZ colour space) are something you have to deal with then this provides and excellent bedrock of colour knowledge.

Free Tektronix UHD/4k info posters

Get 'em here & here!

The Engineer's Bench podcast - "Top Tips; Audio"

Hugh and Phil talk about some tips and get-out-of-gaol-free cards with respect to broadcast audio.
Go to the website for a PDF of the notes.

https://youtu.be/QJO0Z4DuDFc


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

Shooting & editing HDR via Avid using CLog gamma

We've got BVE2016 coming up and one of the things Root6 will be showing is an HDR workflow via Media Composer using Canon monitors.

HDR is still a bit of a crap-shoot as far as standardisation is concerned with the BBC/NHK system, Dolby Vision, Sony's SLog3 and Canon's camera-native CLog. The principle of using an alternate gamma so that you concentrate the bit-depth where you want the extra range is well established;

The hope is that all of these manufacturers will coalesce around ST.2084 which (amongst other things) defines how you handle the specular highlights; those very bright parts of the picture which give a real addition to the look of the pictures. These are typically defined to be >500 Cd/m² which is MUCH brighter than broadcast white! The idea is that the last bit of dynamic range (10th bit - all values above 512) represent the highlights and everything up to 50% is akin to the usual video dynamic range. You calibrate the monitor such that 50% is set at 100Cd/m² and just hope that the colourimetry of the highlights tracks RGB-wise!

So - Root6's own Dave Skeggs and I set off around Soho and London Bridge to capture some night time and daytime footage. We were using a Canon C300 mk.2 set to UHD (3840 x 2160) at 25P (no interlaced fields at UHD and no high framerates at that resolution unfortunately). We set the colour space to an optimistic Rec.2020 and gamma to Clog. In that mode the camera shoots 410mBit/s XAVC codec MXF files.
We've been using Media Composer v 8.5 on an HP Z840 workstation & the new Avid/BlackMagic DNXio video hardware; we had to update the firmware to get it to generate quad-link SDi. Although HDMI works it is nobbled down to eight-bit and so would not be suitable for this test. I would put a link to the video but none of the video sharing sites support HDR and neither does the screen of your tablet/laptop/TV! I took all the monitor photos with my Fuji bridge-camera in a very bright office; you'll have to take my word for it!

Notice the headlights of the taxi - you can see details inside the light!

exactly the same frame; notice the dark details in the trees against the night-sky.

 Of course on Media Composer's GUI display you get the CLog gamma rendered as if it was Rec.709 and so it looks very washed out and lacking in detail

You can have Avid flatten the gamma of source clips so that it looks OK on the GUI - that doesn't affect sequences that the clip mas been used in.

 

Quite a large range of alternate gamma and colour spaces

 It shows up in the bin-view which is useful

 

So now clicking the source window and setting the monitor to regular HD gamma (BT. 1886 fact fans) shows you what the same material shot on a "regular" camera would look like; very little detail in the blacks and none in the whites.

 

 Root6's own DOP; Dave "is that in focus?" Skeggs

I'd forgotten how limited a normal video-camera's dynamic range was. The Canon monitors top out the specular highlights at 400Cd/m² which is somewhat less than a Sony BVM-X300 (1,000 Cd/m²!) but for €10k less than the Sony (and losing only a stop-and-a-half of specular highlights) the Canon 30" UHD/4k IPS panel represents superb value. I was a bit disappointed that the camera tops out at 29.97P at >2k resolution so I couldn't see how nice fluid video motion looked at high res; everything has a jerky film-look to it.
Steve Shaw at Light Illusion has a very good article exploring some of the fundamentals of HDR.

They broke multicast PING in El Capitan (well, kinda!)

I've written in the past about how much I rely on the multicast PING for getting the basic network settings out of a piece of equipment (that's has come back from a customer in some unknown state). Imagine my horror when I discovered they've broken it in OS-X v 10.11 El Capitan.

 So, here's the setup, piece of gear connected directly via an Ethernet interface to my laptop (with a hard-set IP address). Ordinarily using;

PING 224.0.0.1

would force the equipment to respond with it's IP address. Then it's easy to change your laptop's IP to be on the same subnet and you're in (like Flynn). No worries that the computer and equipment are on different subnets, multicast PING forces it to respond.

It appears I'm not the only one to notice this. See here on Apple's support site.

So here's the answer; you can see the effect "No route to host", then I attach to a pocket-router with only the Amulet box on it and by attaching to it over WiFi (it's a router, no need to worry about "wrong" IP subnets) I can PING and determine the Amulet is on 192.168.6.102

I can only assume that by now having an ARP table in the way (the pocket-router) we have a source of H/W address to IP conversion. When there was just a cable between the devices and hard-set IP addresses multicast relies on the second device to answer the broadcast PING with it's H/W address in the return packet. I can only assume that OS-X 10.11 ignores that and instead does an ARP equiry of the router to match the H/W and IP addresses?

It's not a big deal as I do carry one of those little pocket routers in my rucksack as they are supper useful for lots of things;

• Isolating yourself from an (untrusted) client's network
• Isolating an untrusted machine from your network whilst working on it
• Making wired-only demo equipment wireless to aid in customer demos
• A source of IP addresses when lashing up an ad-hoc network.

Blackmagic iOS app works with Barnfind!

Super-impressed with how open Barnfind are over other manufacturers. I wrote before about how they work with Blackmagic control panels, but today for a demo I pointed the BM app at the BF chassis and it's all good.

Audio over cat6a cable?

My podcast-partner in crime, the mighty Hugh Waters asked me how often I run audio signals over twisted-pair data cable in media facility builds. Has has a customer who is eager to do it this way.

I’ve done it a few times and it’s fine with a few considerations.

1. Earthing is still important and since IT people have no idea about proper grounding it can be an issue. If it’s a cat6a install in a TV facility done by me I’d have no worries, but the average IT install might have issues. But as four twisted pairs with individual screens cat6a is ideal for audio. It’s the other parts of the facility I’d worry about,
2. RJ45s don’t have the same DC/LF performance as a good old B-gauge (or Bantam) connector; if the circuits are going to be patched often I’d be wary – mechanically they aren’t great next to traditional audio connectors, 
3. From a wiring perspective; how do you nicely terminate into XLRs from a piece of cat6a?
4. Track shuffling is hard,
5. AES – just fine. Cat6a has an impedance of ~100Ω per pair, ideal for twisted-pair AES. Same observations as 1, 2 & 3.

There you go. I did work at one facility where the engineer had got obsessed with structured cabling and did everything he could over cat6 – analogue video (via baluns), audio, RS422 etc. He liked the idea that you could patch an offline i/o with two RJ45s (stereo i/o on one and video i/o and remote on the other). It didn’t work well and I put in proper cabling and patching after a year.

Sometimes convenience blinds you to fitness for purpose.

Extending wireless networks; some gotchas

Visiting the family over Christmas and of course there are the tech-support duties. One of which was making a wireless network extend further through an old house with very thick walls. In the small amount of time I had there wasn't the option of running network cables to some strategic points where additional WiFi access points could be installed so I invested in a couple of Netgear wireless extenders. 

I've used these before and been impressed; fast throughput and lots of features. They are proper NAT routers and you can use them as firewalls between ethernet network segments or extend an existing wireless network. In that mode (and it's a small switch that sets that mode) the ethernet ports become wired outlets for the WiFi network; intended for set-top boxes that can't be connected via a cable. They can turn a USB drive into a NAS drive and all this for less than twenty quid!

The only downside is that they have a single radio and so can only repeat a network on the channel that it arrives as. In a relatively WiFi-free environment you'd think this wouldn't be a problem, but I didn't figure on how rubbish the provided BT HomeHub 3 is! 

Since they have a flip-out antenna I figured I'd place one downstairs and one upstairs as close as possible to the room with the aDSL router and see how I got on. 

• It is a cheap, plastic, single-board gadget
• It has no external antenna or even socket for one
• You have to use it as the BT mothership monitors for their own secret sauce

What I discovered after two days of frustration is that it is entirely intolerant of other devices sharing it's channel. The Netgears can only repeat on the channel they receive on and so I was off to a non-starter. I would work for a few hours an then both of the Netgears would drop off the network and a round of re-booting (and half an hour for them to all settle down again) told me that this was not a reliable configuration for non-technical users.

So - after a bit of chin-scratching I came to this configuration;

• Netgear no.1 is wired to the BT hub and set for Access Point mode; it's re-serving the connection with a new IP range and (crucially) a new WiFi channel some distance from the BT hub.
• Netgear no.2 is set for wireless extender mode and is located at a mid-point in the house repeating the signal from no.1

This has been stable for more than a day now (I've insisted that my boys use the furthest repeated network) with only minimal speed loss (typ. 8 mbits^-1 against 10mbits^-1 at the BT) so I'm going to run away and hope!

Colourists are the last people who should have a say on monitors!

I was recently in a decent grading room - Dolby PRM 4220 monitor and I was demo'ing a Boland BVB25 OLED display. The demo unit had come back from a try-out at another customer's and I hadn't had a chance to check it's calibration (Rec.709, illuminant-D yada yada...) and so I grabbed the colour probe kit and calibrated it whilst chatting to the engineer and colourist. Once done I looped it off the Dolby to see how they compared and they were quite different! The Dolby was sat-up, over-saturated and a bit red-in-the-whites. The conversation went;

Colourist:"It doesn't match my Dolby",
Me:"…you just watched me calibrate the monitor for Rec.709",
Colourist:"It's wrong",
Me: "Is the Dolby set for Rec.709?",
Colourist: "No, I feel that when I export Quicktimes for customer approval how I have the monitor set now matches what they see better"

 I also have the same convesation about black levels endlessly. An online editor had a go at me because I'd left his monitor "too crushed in the blacks" - here is a frame from his timeline;

It is a continuous battle to persuade people that monitor calibration is NEVER a matter of opinion, rather it is defined by measurable technical standards and when I calibrate a display it is correct. Your material may well not look how you want it, but don't corrupt your monitoring pathway to make your project look good.
Often I'll ask the colourist what standard they want the monitor calibrated for; it's rare that they know what I'm talking about, but they'll often venture an opinion that their display is currently "too cool" or something (quite how they know without a reference I'm not sure?).

I suppose a lot of this is down to the fact that colourists are people who have to be very confident in their ability and are paid handsomely for what they do. However, they have to realise that their mojo doen't extend to how their monitors are set up. When I demo a monitor my heart sinks when someone says "we'd better let the colourist have their say" - monitoring is not about creative magic, it's about compliance.
This December I've calibrated over thirty customer broadcast displays; I've been there/seen that more than you!

Gotchas with updating firmware over RS232

I've recently been upgrading Boland BVB25 OLED monitors over their RS232 serial ports; aside from needing a USB/serial adaptor (I use the Keyspan which mimics an old PC serial UART) you also need a null-modem cable (i.e. where Tx and Rx are swapped over). You can tell if a null-modem cable is required by the sex of the connector on the back of the equipment. A 25-way or 9-way D(male) indicates a DTE ("Data Terminal Equipment" - a PC or terminal) and a female connector a DCE ("Data Communication Equipment") - a modem in RS232 speak. So, if the gear is a DTE then you need a F-F cable and by definition is has to be a cross-over (AKA "null modem" cable. I've banged on about this in the past, and there is also the consideration of handshaking; does you gear/app need the hardware pins (DSR, DTR, DCD etc) or does it use software flow-control (XModem etc). Hugh and I did a podcast on the subject if you need to brush up on your serial comms.

Anyway, because RS232 is such a low level way of doing things it's often the case that the receiving UART in the equipment can get direct memory access before the OS has loaded and you may need to jump through some hoops to get the thing into "serial update mode". In the case of the Boland monitors we sell it's necessary to have the updater software running and looking for comms before you do a power-down reset of the monitor; and not just power-down - tug the power cord, and then within a second or so of re-applying the power the monitor will start talking and appear dead from it's front panel but stuff is going on.

This kind of three-finger tomfoolery really reaches a zenith when you're upgrading the Linux SOC kernal on Amulet DXiP cards!

4k and UHD cabling and signal standards

I've had to dig into signal transport for 4k/UHD over the last week or so. Essentially I have a test-signal generator (SRI Visualizer TG100) running at a maximum raster of 4096x2160 at a maximum of 25 progressive frames/sec (and only 4:2:2 colour sampling; Y, Cr, Cb) with a 6G single-link output (so really 4 x 1.5G links) and HDMI 1.4 (so the same raster as the SDi). The monitors are the 24" and 30" Canon IPS 4k native monitors.

The Canon monitors will take quad-link HD/SDi and (in the case of the 24") HDMI. So, feeding the SRI single-link into a Blackmagic 4k multiplex (to produce quad-link) and then into the Canon produces four quads in the wrong colour-space!

 For an insight into what the multiplex is doing it's worth looking at the two standards for quad-link SDi. Put aside if it's 4 x 1.5G or 4 x 3G (that allows an increase to 50 or 60P OR 4:4:4 colour). But, in this case we're de-mux'ing a 6G to 4 x 1.5G signals. 

The original 4k-over-four-BNCs standard

The more recent standard; each link looks like an HD version

Clearly the converter is producing 2SI but the Canon expects SD quad-link. In fact the guys at Canon tell me they have a firmware update early in 2016 to address this. The other error is that the Canon has mistaken the 4:2:2 video as RGB - but it has at least got the raster correct.

So, what to do? Well, by throwing in another converter and taking the HDMI out of the SRI means the BM mux will get an older SD quad-link input;

This produced what we need; clearly HDMI has not concept of mutliplexed pixels and so we're now fully in SD quad-link;

tugging BNC no.4 shows the monitor is now in quad mode

The monitor gets it all right

The other thing that you have to pay attention to in "True 4k" displays (for the film snobs!) is that feeding 3840x2160 signal into a 4096x2160 monitor and letting the monitor scale-up to fill the line risks killing your resolution;

The aliasing should only the present in the top-most block, the other alias frequencies you can see here are due to my iPhone's camera!

Some very strange aliasing when a 3840-pixel line is mapped to 4096 pixels

As ever with display devices, pixel-pixel (native resolution) is always preferred

Barnfind integration with third party control panels

Barnfind are one of the products I'm responsible for at Root6 and I love them for their forward looking attitude and the fact they embrace open standards; if you see an SFP hole or a BNC connector you know that it will work with any other manufacturers (unlike Evertz who re-define the standard and put an X at the start of the product name!).

So - the BarnOne BTF1-07 is the chassis I have in my demo kit and at IBC this year Wiggo and the guys were showing a much wider set of third party control panels they have integrated to work with their cross-point router. So, to make our demo more compelling I bought a BlackMagic VideoHub Smart control panel and set about making it talk to the BarnOne.

Since I have to rock-up at customers' facilities to show this gear I figured it's daft to rely on their networks and so I've included a TP-Link travel router to dish out IP addresses to the panel and the BarnFind; it also allows you to use a wireless laptop to then run the demo. These little gadgets have single WAN and LAN facing ports but rather splendidly the BlackMagic panel has a little ethernet hub inside so you can loop the network connection to the Barnfind. 

This screen-grab is from BarnStudio - the config/control software for Barnfind products. It has a discovery protocol so it can find any chassis on the same LAN segment. However - I discovered a couple of gotchas;

• When upgrading the chassis you can either attach a USB stick to the front and the embedded Linux machine will grab the image OR you can use BarnStudio. Initially I couldn't get either to work! 

• Barnstudio just instructs the Linux machine to do an apt-get (or similar) and so it has to be able to see out to the internet; connect the WAN-side of the little router to the workshop network!
• If you do the USB route then the installer checks the signature on the package; again, it needs to get out to the web to verify the cryptographic signature.

• The Blackmagic panel does not have any host-discovery protocol built in and so it seemed only sensible to set the router to always dish out the same MAC/IP address combinations by using the DCHP reserved assignment page in the router. Then assign those number in the BlackMagic config software.

After that it really is very simple - you set the virtual buttons to be whatever sources and destinations you want. You can even reserve some to be macros (which are then just a list of route assignments) - in fact that is how you would do duplex signals; Ethernet etc. You have to assign both the in and out of each SFP (Tx and Rx). You don't have to have sequential sources or destinations and I can't honestly see how they could have made it any better!

So - with BNCs 17 & 18 on the front of the Barnfind defined as 3G HD/SDi video in and out and these button assignments on the BM panel I've got proper router control. These forty-button panels will be very useful for controlling all the synchronous broadcast signals (HD/SDi, HDMI, MADI etc.) and asynchronous data signals (Ethernet, fibre-channel etc) running through a Barnfind router (and then out and over CWDM fibre?).

The only criticism is that the software matrix takes a second or so to update after panel changes are made; but I can't honestly see when that would be an issue - this software matrix is  tool for the engineer, not the operator.

As an aside they have recently published a very complete integration guide with lots of examples and advice.

http://media.barnfind.no/marketing/BarnGuide%202.0.pdf

Colour of the wall and lights in grading rooms

In the last year or so a lot of my time seems to have been taken up with getting monitors and other display devices to show the correct colours for film and TV. However, as with all other areas, context is everything and the colour of the wall behind the monitor (and the colour of the light illuminating the wall) are as important as the calibration of the monitor.

Picture from Robin at Wire Broadcast - Grading Suite at Envy

Nobody has perfect colour memory (remind any colourists you know!) and if the rear wall of your grading room is slightly yellow your eyes will adjust to that and you'll tend to grade pictures as if yellow is white and in truth your pictures will be missing blue. So - what's the standard? ISO 3664:2009 specifies "N8" as the neutral grey for accurate colour environments. Essentially you want a paint that favours no reflected colours. You can spend big bucks buying the approved paint from eCinema or RPimaging but you'll wind up spending many hundreds of pounds for a few cans of paint and it isn't really necessary.  I've had splendid results with Crown Plain Grey 5574 Matt Emulsion. In fact ColorTechnics specify that paint for use with their VeriVide D65 “Artificial Daylight” CIE daytime illuminants fluorescent tubes.

Having said that I've never bought the approved tubes, preferring to go to the electrical wholesaler and pick up normal shop-type ones. It turns out that the pet-store industry favours D6500 colour tubes as the light output stretches down into the UV end of the spectrum (sub 300nm wavelength) which animals respond well to. One thing that I have been told is that there is small variance between batches and so it's best to overbuy so that once you've got the holders and baffles fitted you should visually (or using a photometer) make sure the colours are matched. It takes only around 100k of difference for you to be able to spot it immediately and so it's not surprising the manufacturing tolerances are not good enough for TV.

So - wall painted, florescent tubes fitted; what next - well, since you're looking for around 15-20% of the light output of the monitor as a surround (so around 20Cd/m² from the wall) you need a way to control the brightness of the tubes. You could dim them but there is always the risk of the switching waveform breaking through onto your audio system AND tubes change colour as they are dim'ed (particularly as they age) and so the best thing is to fit mechanical baffles to them; Bryant do some excellent ones - but throw away the tubes as the ones supplied at 6000k colour temperature; a tad too red for grading suites.

There are a few other things people obsess about when setting up grading rooms;

1. The Tek WFM601 used to come with an option for a white display (quite a lot more money IIRC) so that the colourists eye wouldn't be drawn by the green phosphors!
2. Computer monitors - you should run them dimmer than the 200Cd/m² peak that most people have.

I'd agree with the second point, but the first one seems unnecessarily picky.

Of course, the biggest offense to anyone who cares about colour fidelity in the film and TV world are these things, Philips Ambilight TVs!