Colour Management Tips
If you have any queries related to the information contained within it or you would like any of the colour management points mentioned to be covered in more detail in a future blog post or guide, please get in touch with our team of experts. Here at Parrot Print, we’re always happy to hear from fellow photography enthusiasts! In the meantime, let’s start at the beginning…
The Human Perception of Colour
Colour management is a complex subject but with a little understanding of the science behind it, it’s easier to apply some of the basics to improve your work, which is why we are starting with how we as humans perceive colour. You may have briefly studied the science of light at school and if you did, you’ll be aware that light is made up of wavelengths that form part of the electromagnetic spectrum, this includes x-rays, radio waves, ultra violet (UV) waves and microwaves, to name but a few. When talking about light, we measure these wavelengths in nanometers. Our eyes are capable of perceiving wavelengths of 400-770 nanometers.
When we see light, the colour of the light depends on three elements: the source of the light, the object we are viewing and our own perception of the light reflecting off the object as the observer. Firstly, looking at the source of the light we see shorter wavelengths as bluish light, longer as reddish and all wavelengths together as white. However, we usually perceive light’s interaction with objects rather than light sources and objects themselves alter our colour perception by reflecting, absorbing or transmitting light. The original light source will direct what wavelengths are reflected or transmitted by an object, but the object itself will process them differently. For example, a ball that is blue reflects most blue wavelengths and absorbs those in other colours. Colours that are the same can look different under different light sources or the same under one light source but different under another – this is called metamerism.
In our eyes, light sensitive cells called rods and cones work to help us recognise colour. Rods work to recognise changes in light and dark and three types of cones are sensitive to wavelengths that appear red, green or blue in shade. This is why we talk of colours being made up of RGB strands. The brain interprets this information together to decide what colours it sees, though it can sometimes get things wrong.
As individuals, our own perception of colour can change over time as we can start to interpret the wavelengths we turn into a sensory perception differently. And, even though we’ve given specific combinations of wavelengths particular names and recognised them as a specific colour, we have no way of knowing we interpret them in the same way as other people.
Printer and monitor calibration: Why?
Calibration is the process that helps you match what you see on screen with what comes out of your printer. When you have a profiled printer, your printed image resembles more closely the image that you see on your computer monitor or other device when editing. Colour management software has come a long way in making this an easier process.
So why do you have to calibrate your printer and monitor? Even if you haven’t printed images at home before, you might have noticed that your home printer and office printer produce slightly different colours even when you’ve selected the same colour on screen. You can reproduce colours more accurately with colour management, and ICC based colour profiling helps you do this. Recognising the difficulties inconsistent printing caused, the International Colour Consortium went to work developing a solution to reproducing consistent images when working with computers, so that colour was independent of the device being used. They developed the ICC computer file format, which holds information that tells a device how to interpret and reproduce colour for consistency purposes.
How to calibrate your monitor
Before you get started with calibration, you should test that all of your devices are working consistently, you don’t want to try and calibrate without doing this, as it’s the equivalent of running towards a moving goal post! Once a device has been calibrated it can be profiled, but the first steps are to adjust your monitor so that optimal colour temperature, luminance and gamma values are discovered and defined.
Warm up your monitor - depending on your device this should take around 30 minutes. Ensure all energy saving settings and screen savers are turned off. Wipe your monitor clean so that you can be sure you are viewing things correctly and change your desktop pattern to grey. If you see any unwanted hints of colour (colour casts) it might be time to upgrade your monitor. You should have your screen resolution at your preferred setting and as the light conditions around you will impact how you see colours, ensure your monitor is the brightest source of light within your field of vision. This may mean you have to dim the light in your room slightly. There are a great number of affordable software options for calibration available now and we recommend the X-rite i1 Display PRO to help with monitor profiling. Once installed, you should follow the bundled automated software prompts, allowing you to custom select your values.
You will set your colour temperature by defining the white point. This helps you match you monitor to the temperature of your ambient light, which is the light source you will view your print under. For most monitors, 65000k is a good white point to choose as it is the temperature most RGB profiles are set to. When it comes to selecting your gamma setting (tone curve) 2.2 is a good setting. Go higher and it may give too much contrast and lower and it could become palid.
Setting your luminance will usually involve lowering brightness, which will help lengthen the life of your screen. Generally you should start with a value of 80-120/candelas per meter squared for brightness. When you have a dimmer ambient light you’ll be heading to the lower end of the range and a higher ambient light means you’ll weigh in at the top end. Once your values are set, you should be able to name and save your profile for future use.
Proofing your print to ensure things are picture perfect
The proof of the pudding with calibration is of course in the printing and you’ll need to follow a few simple steps to ensure you conduct a fair test, once you’ve calibrated your monitor. If you’re working with Adobe Photoshop it usually converts the image’s profile to the monitors. The range of colour on a standard monitor will usually be more than your printer is capable of printing. To get your monitor to reflect the image that the printer will achieve, you have to turn convert the image profile to the printer profile and then to the monitor profile. To do this, go to view>proof setup>custom. Select the printer profile and render then select Simulate Paper Colour. This will change your screen to better match the print.
Without a printer profile Photoshop won’t know how your printer and paper reproduces colour, so you need to give it this information. Once your profile is selected, do a test print and compare with your monitor to see if things match up. If you don’t have a viewing booth, place your print in a window for daylight and then go back to your monitor. Don’t hold your print by your monitor, if you do this your eyes won’t be able to adjust properly to the fact they have different light sources. If your print looks too warm or yellowy – drop the colour temperature, if it looks too dark amend the brightness.
Colour management and Adobe Photoshop
Adobe Photoshop is one of the most popular photography editing suites, yet many people don’t use the colour management settings of the software to their full potential. To help you make the most of yours, here are a few hints and tips for tackling Colour Management in Photoshop.
Choosing colour settings
You can alter you colour settings in the edit menu where you select working space profiles. sRGB is the most common of these; it’s the working space profile used by most printers and cameras. There are other options (including a host under the ‘more options’ button) but sRGB is a good choice because many printer drivers will automatically assume you’re sending data in sRGB.
Colour Management Policies
When opening images that are tagged/untagged with profiles, the behaviour is generally decided by the three colour management policies RGB, CMYK and Gray & Spot. However, you can override these. You should generally embed profiles into your images when you save a file so that the next person who opens it is able to use the embedded profile and knows what colour space you intended to use with it. As most RGB files have to be converted before they arrive at their destination (eg printing) it’s a good idea to have the file embedded and profiles are only usually a few kilobytes in size.
With ICC profiles, colours from one profile colour space can be amended to fit another’s using rendering intent. If you’re translating large RGB colour spaces to smaller CMYK ones, you’ll want to use Perceptual intent. The default in Photoshop is Relative Colorimetric, which allows the colour scope of the destination profile and the source to be unchanged, those that are outside of the scale are translated to the nearest colour. Overall this makes for fewer changes, though colours that are very saturated can lose definition.
Use Black Point Compensation
If you want to retain better definition while using Relative Colorimetric rending, try choosing Black Point Compensation (available in some Adobe applications). This maps the full source colour profile to that of the destination profile.
Setting up a proof
Customised profiles allow pretty accurate soft-proofing on screen with Photoshop and with the options in Proof Setup (found in the View menu) you can see on screen how your RGB images should print. To see how your image will print, select the Custom menu and choose the custom printer profile, you can ask your print company for their RGB profile to enter here. The conversion options you would usually use to change your image from current profile to destination profile can also be selected. This means you’ll have a soft-proof to view how the file will look if processed by your chosen printer and will also have files in RGB working spaces for retouching.