Colour Managed Workflow







Colour Management

Two words that are guaranteed to strike fear at the very core of the modern photographer and a subject that requires a whole book to understand – so let’s get the basics down in one page and chuck the stuff you don’t need out the window.

RG What?

The first thing people realise is that colours can change between camera, monitor and printer – sometimes quite significantly.



Your monitor uses RGB light signals to convey colour. Each colour has three values of Red, Green and Blue and each value is placed somewhere between 0 and 255. So pure white would be shown as 255,255,255 while absolute black would be 0,0,0.

This absolute Blue shown here would be Red, 0, Green, 0, Blue 255....
...but the mid blue below that is Red, 0, Green, 174, Blue, 255. It’s a little like mixing paint and with these three colours your monitor can show millions of colours. It's not dissimilar to the way in which our eyes record colour - which is handy.

Now to complicate matters your printer and professional presses apply colour using CMYK inks – Cyan, Magenta, Yellow and so as not to confuse you the K stands for Black. CMYK devices produce colour in much the same way as RGB devices by mixing the three colours and black using values of 0 to 100 (Black is 100,100,100, 100 and I bet you can guess the white values).

MEASURE YOUR MONITOR.

The first step in a Colour Managed Workflow is to calibrate your monitor and there are two main ways of doing this.

The first is by sight. There are websites that provide greyscale charts and would be targets and of course there is Adobe Gamma for Photoshop users and for MAC users inbuilt programmes such as Colorsync and Macintosh Calibration Assistant. Some graphics cards will also have software that allows some colour control. On the plus side they are cheap but on the negative side they require you to be right in what you perceive on screen. Now if all you are going to do is print at home and never ever share your photographs or supply them to any outside user, then it just might be that this is the way forward for you – after all if you’re happy then what the heck, right? The problem comes when other people start to see your work on their monitors or you send them to a photographic print company and you find out that your eyes are not all that good at monitor calibration.

So the next step is to buy a hardware calibration kit and there are quite a few of them out there and even more confusing is that some are related and as with all things there are varying levels of control and usability; but at their heart they all do much the same. Each of them will measure the colour values coming from your screen and create a profile that will make your monitor as close as it can be to an industry standard colour display. All I can do here is say, take your time and read the instructions first. There are, however, steps that we can take to help you and your monitor calibration to be first, correct and secondly, stay usable.

It’s best to work in a neutral light and one that doesn’t alter too much in the course of a day. Try and keep bright spots out of your peripheral vision. Avoid having anything that will reflect from the screen and use a mid grey background for your desktop not some lurid bunch of daffodils for instance.

It should be easy to see the 2% differences between each grey block and the RGB midgrey is marked

During calibration many of the devices will ask you to choose a White Point, Gamma and Luminance settings, if yours does this for you, then let it – if not, read on.

There is no absolute correct value for any of them. Thankfully the whole point of calibration is to get a profile that suits your workflow and as most of us will be printing to an inkjet we can make some decisions based on that assumption.

A slightly blue white point of 6000-6500K will suit inkjets (5500K would suit those working in Press Proofing) and cope with the brighteners that are used in modern print paper.

Luminance is dependant on viewing conditions and ambient light but for most everyday users it’s advisable to aim for a maximum on your first calibration and then find the cd/m2 value that suits you in a subsequent calibration.

Even Gamma varies with print output and viewing conditions but the safest choice is the traditional 2.2 even on modern Macs which inherently used 1.8.

With modern LCD monitors we run into Native White Point and Gamma and many users will find this the easiest choice. It will settle on a value that is comfortable for your monitor and keep away from the edges of its capabilities and therefore not run the chance of introducing annoying problems. It’s something of an average compromise but can be a safer choice.



Some devices will also let you build a custom Gamma curve and some users will run into L* Gamma which is an automated way of constructing gamma separate tone curves for shadow, mid tones and highlights. If it's there, use it.

But if in doubt – White Point 6500K, 65K, D65. Luminescence target of around 100-140cd/m2 and a Gamma of 2.2.

SPACE.

We can go back to RGB again, only this time it's Adobe RGB and it's down to the choice of Colour Space that you work in, what Photoshop and the like call your Working Space.

The ultimate colour space is CIE-Lab* (Commission Internationale de l'Eclairage) and it's basically every colour that our eyes are capable of seeing. Now imagine that within this wide-ranging gamut of colours are other colour spaces that envelope a certain section of that gamut but not it all. There is nothing more complicated to Colour Space than that. Adobe RGB will encompass more of those colours than sRGB while ProphotoRGB has a wider range than AdobeRGB.

We can generate a 3D model of the CIE-Lab gamut, depicted here as a wire grid and inside that I've placed the model for the RGB colour space.

So which colour space is right for you? The easy way is to simply choose Adobe RGB and have done with it but we'll look at the whys and whens. AdobeRGB has better saturation in print in the Cyan/Blue and Yellows. It's something of a Professional Standard and photographs saved as AdobeRGB images will make you future proof as more and more capable devices come on-line. You can switch an AdobeRGB photograph down into sRGB but you cannot do the opposite and gain any extra colours. The preferred colour space for press conversion to CMYK is AdobeRGB.

The sRGB colour space inside the RGB space.

There are some Howevers, however. If your camera only captures sRGB images then you might as well continue that colour space right through your workflow. You will gain nothing from 'upgrading' that image in Photoshop or whatever software you use. If you intend your photographs to be seen on the Internet, then you need to convert your image into sRGB and when you make that conversion you might just see the change in colours as the saturation is taken out of those blues and yellows. And there are more RGB colour spaces such as Colormatch and the increasingly used ProphotoRGB that uses more of the CIE-Lab colours than poor AdobeRGB. ProphotoRGB is fine if your output (Printer) is capable of using the wider range of colours, because of course much like your camera and monitor it will have it's place within the CIE-Lab gamut. Every device is capable of showing a percentage of the whole colour spectrum and those profiles will cross each other and also occupy a singular space within the gamut and it's those areas where one profile falls outside another that causes us problems.

The RGB space inside the ProphotoRGB space. it's easy to see how much bigger than AdobeRGB it really is.



PROFILED, PROOFED AND PRINTED.

So you have your images in RGB, your monitor is working and now you need to print and still keep that colour workflow intact.

You’ll need an ICC profile for the paper you’ve chosen to use. If, for instance, you’ve got an Epson printer and you’re using Epson paper then the ICC print profile for that paper is very likely already installed along with the drivers for the printer.

If you’re using another manufacturers paper then you’ll need to either visit their website and download the profile for your paper designed for your printer or have a custom made one written. Installing an ICC profile is easy. Download the file to a suitable folder, right click and choose install, otherwise they need to be in Windows>System32>Spool>Drivers>Color

Without getting bogged down in facts and figures it's worth just clarifying what an International Color Consortium profile (ICC) actually is. In short it takes the output from one device and converts it into the colour space of another. We can measure any devices place within the CIE-Lab colour space and use that information to make the required alterations that allow us to swap information from one device (monitor) to another (printer). For most people the ICC profiles supplied by the paper manufacturer will be enough but it is true that no printer is exactly the same as another, even identical models, and so it is possible to build a printer specific profile and just like monitor calibrating there are two ways to do it. By sight and by hardware.

Some Raster Image Processing Software(RIPs) will show gamut range problems between varying color spaces and output devices. This lets you make changes before you waste expensive ink.


Writing your own profile is nothing more complicated than printing a target, deciding what is wrong with it, correcting and then repeating the process until you arrive at an output that you're happy matches your monitor output. Your print driver will then have the option to save those alterations as your own paper profile. The alternative, and it's the one if colour and tonal accuracy is important to you, is to have one written especially for you and your printer. Target colour patches are outputted on your machine and then read with a Spectrophotometer. The results are then used to create the ICC profile that allows your printer to deliver true results time and time again matched against a control print - a matchprint.

Before you print, you can use Photoshop to Proof your photograph. In other words, get the software to show you what your print will look like on a particular paper, allowing you to make the necessary alterations.

(I’m using CS2 here but it’s the same method in CS and 7. I’m leaving CS3 alone for now as 7, CS and CS2 are likely to remain the most used for some time yet.)

To start with we need a blank Photoshop with no images opened. Now go to View>Proof set-up>Custom.


Then choose a Profile (Device Simulate) from the drop down. Set Rendering Intent to Relative Colorimetric (we’ll come back to that one) and make sure that Simulate Paper Color and Black Point Compensation are ticked and now save the Proof with a suitable name.



Photoshop should default save to a folder called Proof. While you’re in Proof save mode you might as well create and save a whole load of Proofs while you’re there.

Now when you open an image click on View>Proof set-up, you’ll find your creations are at the bottom of the list. Tick the one you need to use and you’ll see how your photo will print on that particular paper, you can even use View>Gamut Warning to see if there are any colours out of range on that media and make adjustments to the Hue and Saturation to bring them back in line.



Don't forget that those alterations are likely to apply to any image using that proof so it's worth saving the Hue/Sat layer adjustment as a HSU file that you can call on again. Untick your soft proof.

The final stage in our workflow is the inkjet print and if all your management is in place then it becomes an easy exercise.

With your image open in Photoshop - File>Print with Preview.

I'm using an Epson printer and CS2 for this next part of the workflow but any differences between printer user-interfaces are minimal and the principles remain the same.

You can see below Adobe Photoshop's Print with Preview box and the colour management settings I've chosen.



It's telling me that my document is an Adobe RGB one and I've chosen to let Photoshop handle the colour. Under that I've picked the ICC profile for the paper I'm using (in this case Permajet's Fibre based Gloss) and I've gone for a Rendering of Relative Colorimetric (more on that shortly) and ticked the Black Point compensation. Then I click Print. This leads me into Epson's own Printer interface and here I've turned off the printer's Colour Management as Photoshop, with our ICC paper profile, is telling the printer exactly what we want from it.



Now print.

This process alters when we've constructed our own paper profiles using our printers own software. In that case we choose the Let Printer Determine Colours from the drop down menu still with Relative Colorimetric and then in the printer driver choose our personal profile for the paper we're using - you can see I called this Epson Trial and once I was happy with the tweaks can rename it with a suitable paper name.



Rendering Intent is less threatening than it sounds and they are simply the way in which the ICC profiles deal with colours that are outside the reproducible gamut. For the examples above I've been using Relative Colorimetric but here's an overview of the others and why and when you might choose to use them, or not.

Relative Colorimetric will clip any colours that are outside the destination profile which can result in a flattened image in terms of colour. On the plus side it reproduces matched colours perfectly which is perfect if your destination colour range exceeds your source range.

Absolute Colorimetric differs in that it attempts to simulate the white point of the source profile (in other words the paper that the profiler used to create the profile) onto the destination device, the printer. Relative Colorimetric attempts to use the paper colour of the destination device, in other words they both shift the white point. This shift becomes less noticeable if we were to print a borderless print as any white in the image is not in comparison to the white borders of the visible paper.

Perceptual Intent retains the relationship between colours, in other words the spacing in the values, but to do this and not to clip it drops the saturation in very saturated colours. For photographers it's referred to as the safest choice because it won't clip.

Saturation Intent is worth avoiding in photographic work as it 'squeezes' the colours so as to output a super saturated image. This is great for presentation graphics but that over saturation results in there being less available and lacks subtlety.

The one you choose is to some extent a personal choice and a bit of experimentation will yield comparative results. In time you'll learn how to recognise images that will benefit from Relative Intent..ie...those with a narrower ranging gamut benefiting from the exact colour match and Perceptual...ie... those that use a wider range of colours from which you don't want to lose any through clipping.

And so despite the fact that there is what appears to be a minefield of problems amongst the myriad of colour spaces and profiles, in reality it's very simple to set a colour management workflow in place.

Choose your Workspace RGB and keep it that way between applications. Calibrate your monitor, get the profiles for your papers and don't mess too much when it starts to look right.



If we look at the Colour space profile for a sheet of Epson Premium Glossy and place that inside an AdobeRGB wire frame, we can easily see the amount of work that the ICC profile and the Rendering Intent have to do.


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