22nd January 2015 – On Colour Space

Colour space and gamut. Sounds like a poor man’s crime fighting duo, but as Rich Price showed us it is a surprisingly powerful way to subtly (or not so) expand the presentation of colour in an image. Concentrating on derivatives of RGB, Red, Green, Blue, from which all other colours can be made and moving towards white, there are a number of different models – the basic physics of how we end up seeing the rendering – all existing to do the same job: Turn 1’s and 0’s into recognisable colours on screen or in print ( the model is the printer’s map, the image the contour lines). CMYK mixes cyan, magenta, yellow and black (the K stands for Key ), on the page and is popular with magazines and similar publications, and works by subtracting light from white as the start point. Then things start to get complicated with other models, such as CIELAB and CIE XYZ that approximate human vision in constructing colours and are used converting RGB images to CMYK. In itself all fascinating but not something that we need particularly concern ourselves with in depth.  It gets very technical but is interesting.


So much for the models but we were concentrating on the work spaces. There are a number of them: sRGB – the most common found in display screens and cameras, PhotoRGB, the aforementioned CIELAB and Adobe RGB are a few. Rich concentrated on sRGB, and Adobe with a  brief excursion through ProPhoto which Adobe use between LightroomTM and PhotoshopTM. Prophoto has a very large gamut, in fact 15% of it cannot be seen with the human eye. More is not always better, as with everything else, more is only useful when you have a need for it. If your image is looking muddy it is far, far more likely that you are viewing the narrower sRGB profile in an image that was modelled in the more defined Adobe RBG than the straight forward “fault” of the more limited spectrum. Most people cannot tell the difference most of the time. The gamut of any two profiles will have colours in common but when comparing sRGB and Adobe RBG the number of shades that can be represented between two points of saturation. What the smaller gamut will produce is an approximation of the colour defined in the larger one and necessarily, it will be different. The basis is in the degree of colour gradation that can be shown, that is the number of steps (shades) you can produce in the transition between two (complimentary) colours on the colour wheel. Just for the record the “small” sRGB colour space has 16,777,216 (256 for each of the RGB channels) colours in it.


The most likely time you will see the difference is when you print a digital image. Printer manufacturers have their own profiles and these are usually pretty easy to get hold of – unlike the Linux version of Adobe which seems to have disappeared from their website. These can then be loaded into your editor, the internet will show you how for your programme if you don’t know. Paper manufacturers also have different profiles for their papers and the respective manufacturers web sites are the best places to start with this. What this means is that if you are sending off your treasured image to be printed then you get a heads up on what the final thing will look like through your editing programme. It can change quite a bit, for example, an early morning mist shot I took yesterday, an almost golden light, when reviewed via a Fuji printer ICC profile downloaded from the print shop, showed some of the shadows moving from an almost dark chocolate to cyan – the valley opposite had oxidised! It also saves you time and money when printing at home, and quality inkjet ink is not cheap and cheap inkjet ink can quite often look it, especially on a quality photo paper.


Rich, when he started his presentation, stated that there is an important factor to be taken into consideration when we are talking about colour space, which can easily be overlooked and comes to us from the familiar colour wheel. Colour space is three dimensional, whereas the colour wheel as most of us remember it is two dimensional. The three dimensions are hue, saturation and lightness aka HSL aka HSV (v – value) and they form the backbone of all image editing software. What we are doing when we edit is navigating our way around this space, forwards, backwards, side to side and up and down and in a combination of these three. That gives us a clue that there are work flow questions to be answered here. Work flow in itself is a whole separate blog and we will return to that sometime in the future, but essentially it is all the production, administration and physical actions it takes to complete a process. There are many different forms of workflow, probably as many as there are photographers practising, but, when it comes to colour space there are some basics worth heeding – not least the effect your monitor is having on the images you are viewing and the accuracy and compatibility of colours when your image meets other devices. The club has a device for calibrating monitors which is available to borrow to club members. Ask about it at a meeting if you want to know more.


The second half of the meeting was a practical and members were busily engaged in the delights of LightroomTM and PhotoshopTM and there were more than a few “Aha!” moments. So, our thanks to Rich for his time and energy in putting this together. Next meeting is our own Adrian Cooke who will be talking us through a selection of his images.


Next meeting is also the deadline for Deadline for “Dear Reflex…” questions      “Dear Reflex…” is a question and answer session where club members can ask any photography-related questions of the club. These will later be presented to members who will have the opportunity to volunteer to answer them, and given time to present their answer.


See you Thursday!