Color Temperature

Lightroom Color Temperature (or Colour Temperature if you spell correctly!)

“Andy – why the heck is Lightrooms temperature slider the wrong way around?”

That’s a question that I used to get asked quite a lot, and it’s started again since I mentioned it in passing a couple of posts ago.

The short answer is “IT ISN”T….it’s just you who doesn’t understand what it is and how it functions”.

But in order to give the definitive answer I feel the need to get back to basics though – so here goes.

The Spectrum Locus

Let’s get one thing straight from the start – LOCUS is just a posh word for PATH!

Visible light is just part of the electro-magnetic energy spectrum typically between 380nm (nanometers) and 700nm:

%name Color Temperature

In the first image below is what’s known as the Spectrum Locus – as defined by the CIE (Commission Internationale de l´Eclairage or International Commission on Illumination).

In a nutshell the locus represents the range of colors visible to the human eye – or I should say chromaticities:

1200px CIE1931xy blank Color Temperature

The blue numbers around the locus are simply the nanometer values from that same horizontal scale above. The reasoning behind the unit values of the x and y axis are complex and irrelevant to us in this post, otherwise it’ll go on for ages.

The human eye is a fickle thing.

It will always perceive, say, 255 green as being lighter than 255 red or 255 blue, and 255 blue as being the darkest of the three.  And the same applies to any value of the three primaries, as long as all three are the same.

perception Color Temperature

This stems from the fact that the human eye has around twice the response to green light as it does red or blue – crazy but true.  And that’s why your camera sensor – if it’s a Bayer type – has twice the number of green photosites on it as red or blue.

In rather over-simplified terms the CIE set a standard by which all colors in the visible spectrum could be expressed in terms of ‘chromaticity’ and ‘brightness’.

Brightness can be thought of as a grey ramp from black to white.

Any color space is a 3 dimensional shape with 3 axes x, y and z.

Z is the grey ramp from black to white, and the shape is then defined by the colour positions in terms of their chromaticity on the x and y axes, and their brightness on the z axis:

adobeRGB1998 Color Temperature

But if we just take the chromaticity values of all the colours visible to the human eye we end up with the CIE1931 spectrum locus – a two dimensional plot if you like, of the ‘perceived’ color space of human vision.

Now here’s where the confusion begins for the majority of ‘uneducated photographers’ – and I mean that in the nicest possible way, it’s not a dig!

Below is the same spectrum locus with an addition:

PlanckianLocus Color Temperature

This additional TcK curve is called the Planckian Locus, or dark body locus.  Now please don’t give up here folks, after all you’ve got this far, but it’ll get worse before it gets better!

The Planckian Locus simply represents the color temperature in degrees Kelvin of the colour emitted by a ‘dark body’ – think lump of pure carbon – as it is heated.  Its color temperature begins to visibly rise as its thermal temperature rises.

Up to a certain thermal temperature it’ll stay visibly black, then it will begin to glow a deep red.  Warm it up some more and the red color temperature turns to orange, then yellow and finally it will be what we can call ‘white hot’.

So the Planckian Locus is the 2D chromaticity plot of the colours emitted by a dark body as it is heated.

Here’s point of confusion number 1: do NOT jump to the conclusion that this is in any way a greyscale. “Well it starts off BLACK and ends up WHITE” – I’ve come across dozens of folk who think that – as they say, a little knowledge is a dangerous thing indeed!

What the Planckian Locus IS indicative of though is WHITE POINT.

Our commonly used colour management white points of D65, D55 and D50 all lie along the Planckian Locus, as do all the other CIE standard illumimant types of which there’s more than few.

The standard monitor calibration white point of D65 is actually 6500 Kelvin – it’s a standardized classification for ‘mean Noon Daylight’, and can be found on the Spectrum Locus/Plankckian Locus at 0.31271x, 0.32902y.

D55 or 5500 Kelvin is classed as Mid Morning/Mid Afternoon Daylight and can be found at 0.33242x, 0.34743y.

D50 or 5000 kelvin is classed as Horizon Light with co-ordinates of 0.34567x, 0.35850.

But we can also equate Planckian Locus values to our ‘picture taking’ in the form of white balance.

FACT: The HIGHER the color temperature the BLUER the light, and lower color temperatures shift from blue to yellow, then orange (studio type L photofloods 3200K), then more red (standard incandescent bulb 2400K) down to candle flame at around 1850K).  Sunset and sunrise are typically standardized at 1850K and LPS Sodium street lights can be as low as 1700K.

And a clear polar sky can be upwards of 27,000K – now there’s blue for you!

And here’s where we find confusion point number 2!

Take a look at this shot taken through a Lee Big Stopper:

2 Color Temperature

I’m an idle git and always have my camera set to a white balance of Cloudy B1, and here I’m shooting through a filter that notoriously adds a pretty severe bluish cast to an image anyway.

If you look at the TEMP and TINT sliders you will see Cloudy B1 is interpreted by Lightroom as 5550 Kelvin and a tint of +5 – that’s why the notation is ‘AS SHOT’.

Officially a Cloudy white balance is anywhere between 6000 Kelvin and 10,000 kelvin depending on your definition, and I’ve stuck extra blue in there with the Cloudy B1 setting, which will make the effective temperature go up even higher.

So either way, you can see that Lightrooms idea of 5550 Kelvin is somewhat ‘OFF’ to say the least, but it’s irrelevant at this juncture.

Where the real confusion sets in is shown in the image below:

1 Color Temperature

“Andy, now you’ve de-blued the shot why is the TEMP slider value saying 8387 Kelvin ? Surely it should be showing a value LOWER than 5550K – after all, tungsten is warm and 3200K”….

How right you are…..and wrong at the same time!

What Lightroom is saying is that I’ve added YELLOW to the tune of 8387-5550 or 2837.

FACT – the color temperature controls in Lightroom DO NOT work by adjusting the Planckian or black body temperature of light in our image.  They are used to COMPENSATE for the recorded Planckian/black body temperature.

If you load in image in the develop module of Lightroom and use any of the preset values, the value itself is ball park correct(ish).

The Daylight preset loads values of 5500K and +10. The Shade preset will jump to 7500K and +10, and Tungsten will drop to 2850K and +/-0.

But the Tungsten preset puts the TEMP slider in the BLUE part of the slider Blue/Yellow graduated scale, and the Shade preset puts the slider in the YELLOW side of the scale, thus leading millions of people into mistakenly thinking that 7500K is warmer/yellower than 2850K when it most definitely is NOT!

This kind of self-induced bad learning leaves people wide open to all sorts of misunderstandings when it comes to other aspects of color theory and color management.

My advice has always been the same, just ignore the numbers in Lightroom and do your adjustments subjectively – do what looks right!

But for heaven sake don’t try and build an understanding of color temperature based on the color balance control values in Lightroom – otherwise you get in one heck of a mess.

Nikon D7500

Nikon D7500

D7500 Nikon D7500

All week my inbox has been inundated with emails from every vendor and idiot magazine extolling the virtues of the new Nikon D7500, why I should want it, buy it, and tell everyone else to do so.

In Ephotozines announcement for example,  they state that the Nikon D7500 sits ABOVE the D7200, launched back in March 2015.  And that would be a logical assumption based on the model number wouldn’t it; the D7500 could be seen as the D7200 replacement, or at least a step up from it.

WRONG !

Nikon have been making basically three classes of DSLR cameras, Basic, Intermediate and Professional/Advanced.  Late last year Nikon brought out the D5600 which sat firmly in the BASIC bracket.

The D5600 importantly has:

  • No DUAL card capability
  • No AI/AIS indexing capability
  • No vertical grip capability
  • Body Only price: around £500

The D7200 has:

  • Dual Card Slots
  • AI/AIS indexing tabs
  • A  vertical Grip capability
  • Body Only price: around £850

The NEW NIKON D7500 has:

  • NO Dual Card capability
  • NO AI/AIS indexing tabs
  • NO Vertical Grip capability
  • Body Only price: around £1300

As far as I’m aware the Nikon D7500 is THE FIRST Nikon DSLR body to cost MORE than £1000 that does NOT allow you to use the FULL range of Nikon current production lenses such as the 50mm f1.2 or indeed any of the stellar AI/AIS lenses available on the used market for little money.

Ai Ais Nikon D7500

The AI/AIS tab on the Nikon lens mount – missing on the Nikon D7500.

The D7200 DOES all the above, and the D5600 does not.

Take the Nikon D7500 and swap the 7 and the 5 around and you get a Nikon D5700 – now that’s more like it!

But Andy you’re talking crap – it’s got the brain of the D500!

Yes – so they say, but it’s still got basically the same AF system as the FX D750 and DX D7200 – the 51-point MultiCam 3500 FXII, not the D500 MultiCam 20K.

But Andy you’re talking crap – it does 8 frames per second!

That’s as maybe – but how long can it keep that up for buffering to a crappy SD card?

Nikon have basically ripped the 20.9Mp sensor and Expeed 5 processor out of the D500 and jammed it into a D5600, together with the AF module from the camera YOU THINK it’s replacing, and decided to charge you more than TWICE THE PRICE.

Nice one Nikon!

Yes, image quality wise the Nikon D7500 should kick the living daylights out of both the D5600 and the D7200 if only because of the D500 SNR firmware that drives its image recording.

But at that price???

Believe me – a used D3S would crucify the Nikon D7500 on IQ alone, with the added benefit of dual CF cards and an FX sensor.

But perhaps you don’t want the glorious wide angle performance afforded you by an FX sensor.  If that’s the case then be sensible with your money and get a D500 – used ones are out there at the same sort of money as the new Nikon D7500.

It just shoots for ever buffering to an XQD card, has AI/AIS capability and can be fitted with a vertical grip.  Then the AF can be revved up a bit more by using a big battery out of the one of the FX pro bodies.

You’ve only got to look at the specs for Nikon D7500 to know it’s something of an epic FAIL!

 

Monitor Calibration Update

Monitor Calibration Update

Okay, so I no longer NEED a new monitor, because I’ve got one – and my wallet is in Leighton Hospital Intensive Care Unit on the critical list..

What have you gone for Andy?  Well if you remember, in my last post I was undecided between 24″ and 27″, Eizo or BenQ.  But I was favoring the Eizo CS2420, on the grounds of cost, both in terms of monitor and calibration tool options.

But I got offered a sweet deal on a factory-fresh Eizo CS270 by John Willis at Calumet – so I got my desire for more screen real-estate fulfilled, while keeping the costs down by not having to buy a new calibrator.

%name Monitor Calibration Update

But it still hurt to pay for it!

Monitor Calibration

There are a few things to consider when it comes to monitor calibration, and they are mainly due to the physical attributes of the monitor itself.

In my previous post I did mention one of them – the most important one – the back light type.

CCFL and WCCFL – cold cathode fluorescent lamps, or LED.

CCFL & WCCFL (wide CCFL) used to be the common type of back light, but they are now less common, being replaced by LED for added colour reproduction, improved signal response time and reduced power consumption.  Wide CCFL gave a noticeably greater colour reproduction range and slightly warmer colour temperature than CCFL – and my old monitor was fitted with WCCFL back lighting, hence I used to be able to do my monitor calibration to near 98% of AdobeRGB.

CCFL back lights have one major property – that of being ‘cool’ in colour, and LEDs commonly exhibit a slightly ‘warmer’ colour temperature.

But there’s LEDs – and there’s LEDs, and some are cooler than others, some are of fixed output and others are of a variable output.

The colour temperature of the backlighting gives the monitor a ‘native white point’.

The ‘brightness’ of the backlight is really the only true variable on a standard type of LCD display, and the inter-relationship between backlight brightness and colour temperature, and the size of the monitors CLUT (colour look-up table) can have a massive effect on the total number of colours that the monitor can display.

Industry-standard documentation by folk a lot cleverer than me has for years recommended the same calibration target settings as I have alluded to in previous blog posts:

White Point: D65 or 6500K

Brightness: 120 cdm² or candelas per square meter

Gamma: 2.2

Screen Shot 2017 04 02 at 13.04.25 Monitor Calibration Update

The ubiquitous ColorMunki Photo ‘standard monitor calibration’ method setup screen.

This setup for ‘standard monitor calibration’ works extremely well, and has stood me in good stead for more years than I care to add up.

As I mentioned in my previous post, standard monitor calibration refers to a standard method of calibration, which can be thought of as ‘software calibration’, and I have done many print workshops where I have used this method to calibrate Eizo ColorEdge and NEC Spectraviews with great effect.

However, these more specialised colour management monitors have the added bonus of giving you a ‘hardware monitor calbration’ option.

To carry out a hardware monitor calibration on my new CS270 ColorEdge – or indeed any ColorEdge – we need to employ the Eizo ColorNavigator.

The start screen for ColorNavigator shows us some interesting items:

colnav1 Monitor Calibration Update

The recommended brightness value is 100 cdm² – not 120.

The recommended white point is D55 not D65.

Thank God the gamma value is the same!

Once the monitor calibration profile has been done we get a result screen of the physical profile:

colnav2 Monitor Calibration Update

Now before anyone gets their knickers in a knot over the brightness value discrepancy there’s a couple of things to bare in mind:

  1. This value is always slightly arbitrary and very much dependent on working/viewing conditions.  The working environment should be somewhere between 32 and 64 lux or cdm² ambient – think Bat Cave!  The ratio of ambient to monitor output should always remain at between 32:75/80 and 64:120/140 (ish) – in other words between 1:2 and 1:3 – see earlier post here.
  2. The difference between 100 and 120 cdm² is less than 1/4 stop in camera Ev terms – so not a lot.

What struck me as odd though was the white point setting of D55 or 5500K – that’s 1000K warmer than I’m used to. (yes- warmer – don’t let that temp slider in Lightroom cloud your thinking!).

1000k Monitor Calibration UpdateAfter all, 1000k is a noticeable variation – unlike the brightness 20cdm² shift.

Here’s the funny thing though; if I ‘software calibrate’ the CS270 using the ColorMunki software with the spectro plugged into the Mac instead of the monitor, I visually get the same result using D65/120cdm² as I do ‘hardware calibrating’ at D55 and 100cdm².

The same that is, until I look at the colour spaces of the two generated ICC profiles:

profile Monitor Calibration Update

The coloured section is the ‘software calibration’ colour space, and the wire frame the ‘hardware calibrated’ Eizo custom space – click the image to view larger in a separate window.

The hardware calibration profile is somewhat larger and has a slightly better black point performance – this will allow the viewer to SEE just that little bit more tonality in the deepest of shadows, and those perennially awkward colours that sit in the Blue, Cyan, Green region.

It’s therefore quite obvious that monitor calibration via the hardware/ColorNavigator method on Eizo monitors does buy you that extra bit of visual acuity, so if you own an Eizo ColorEdge then it is the way to go for sure.

Having said that, the differences are small-ish so it’s not really worth getting terrifically evangelical over it.

But if you have the monitor then you should have the calibrator, and if said calibrator is ‘on the list’ of those supported by ColorNavigator then it’s a bit of a JDI – just do it.

You can find the list of supported calibrators here.

Eizo and their ColorNavigator are basically making a very effective ‘mash up’ of the two ISO standards 3664 and 12646 which call for D65 and D50 white points respectively.

Why did I go CHEAP ?

Well, cheaper…..

Apart from the fact that I don’t like spending money – the stuff is so bloody hard to come by – I didn’t want the top end Eizo in either 27″ or 24″.

With the ‘top end’ ColorEdge monitors you are paying for some things that I at least, have little or no use for:

  • 3D CLUT – I’m a general sort of image maker who gets a bit ‘creative’ with my processing and printing.  If I was into graphics and accurate repro of Pantone and the like, or I specialised in archival work for the V & A say, then super-accurate colour reproduction would be critical.  The advantage of the 3D CLUT is that it allows a greater variety of SUBTLY different tones and hues to be SEEN and therefore it’s easier to VISUALLY check that they are maintained when shifting an image from one colour space to another – eg softproofing for print.  I’m a wildlife and landscape photographer – I don’t NEED that facility because I don’t work in a world that requires a stringent 100% colour accuracy.
  • Built-in Calibrator – I don’t need one ‘cos I’ve already got one!
  • Built-in Self-Correction Sensor – I don’t need one of those either!

So if your photography work is like mine, then it’s worth hunting out a ‘zero hours’ CS270 if you fancy the extra screen real-estate, and you want to spend less than if buying its replacement – the CS2730.  You won’t notice the extra 5 milliseconds slower response time, and the new CS2730 eats more power – but you do get a built-in carrying handle!