Colour management || Monitor calibrators || Colour Space || Photo Printers
What a photographer should know about colour spaces
What are the colour models or systems?
What is the RGB colour model?
What is the CMY(K) colour model?
What are the colour spaces?
Which colour space to use for sharing images online?
Which colour space to use for printing?
Aim: This is the second article in the series colour management and printing. The aim of this article is to make you familiar with colour models and spaces as an important part of colour management. In addition, it is discussed which colour spaces to choose for sharing images online and for printing.
Audiences: This article is meant for professional photographers as well as photography enthusiasts with overall knowledge of photography and post processing.
A colour space comprises of all colours (gamut) a device can capture or reproduce.
RGB and CMY(K) are the the two main colour spaces. The first one is used in all digital screens, the second one in printing.
RGB systems comprises of the three important colour spaces: sRGB, AdobeRGB and ProPhotoRGB
Having a basic knowledge of colour spaces is important in colour management in order to ensure the colours remain similar when viewed on different devices (screens, prints) throughout the workflow.
From digital photography to printing we shift from RGB to CMY(K) colour systems, hence it is important that colours are defined (monitors calibrated, colour profiles of the printer and paper matches) across all devices used to maintain the colours.
In the previous article, you became familiar with the definition of colour management, which basically consists of all measures you incorporate in your workflow in order to ensure colours / tones / contrasts remain the same from the moment you take the photo until they are shared online or printed on paper. You have also learned some initial steps in colour management techniques. In this article, I will discuss colour models and spaces. This forms an extremely important part of colour management in digital photography.
How colours are formed in digital and print formats
How colours are formed and displaced on different devices is a complicated science on its own. But for us, the photographers, it is only enough to know the essentials of colours and colour spaces. Hence, I try to explain this and its importance in colour management as simple as possible.
Figure 1. In digital photography there are two colour models any photographer needs to be familiar with: The RGB and The CMY.
THE RGB SYSTEM AND SPACE
Photography, the process of image making, starts with capturing light of different colours on the camera sensor, converting these colours to digital information, transferring the Digital image to a photo processing software like photoshop, and viewing the images on a screen (monitor, tv, smartphone, etc). Up until this stage all possible colours in an image are created by the three primary colours: Red (R), Green (G) and Blue (Blue); hence the RGB system (Figure 1). This is also how our eyes see the colours. Therefore, in the realm of light, all colours are made by a combination of the three primary colours Red, Green and Blue. When these three colours are combined at their maximum saturation (the value you see for each colour in photoshop is 255) they create white. When the values for these colours are zero, it creates black. All other colours created by different combinations of these three primary colours (figure 2).
Figure 2. In a digital image, each colour is a unique combination of the three colours Red, Green and Blue. By placing the colour picker on any part of the image you can see the combination of those three colours. In this image, three samples have been taken from the face and the brightest and the darkest areas of the image.
The RGB systems consists of several important RGB colour spaces: sRGB, AdobeRGB, and ProPhotoRGB (figure 3). Basically a colour space comprises of all colours (gamut) a device can capture, reproduce or display.
sRGB is the smallest RGB colour space and is used in almost all digital screens. AdobeRGB has a much wider gamut and could be considered at this moment the most important colour space in photography. Since, it includes most colours a professional camera sensor can capture and a high end printer can reproduce. ProPhotoRGB is the widest colour space and there are no monitor or printer that can reproduce all colours that exist in this colour space.
Figure 3. This image gives you an idea about how large each colour space is.
THE CMY(K) COLOUR SYSTEM AND SPACE
The last step in photography -for some- is printing. When it comes to printing the colours are made of the three primary colours Cyan (C), Magenta (M) and Yellow (Y). Theoretically, when these three colours are combined at their saturated levels they should create black colour (that is why CMY is a subtractive colour system). However, this is not the case in reality due to the inks’ imperfections. That is why the colour Black (K stands for Key in CMYK) is added to the CMY(K) system. All other colours are created by different combinations of these colours. In order to increase the gamut and reproducing fine details, most high end printers contain more inks (e.g. 6 to 12 inks, including for instance light cyan and magenta). The true white colour in CMY(K) is relied on the white colour of the print paper.
The CMY(K) colour is larger than the sRGB (figure 3). Some printers (in combination with certain papers) are even able to reproduce most of the AdobeRGB colours. But there is no printer -yet- that can reproduce all the colours of the ProPhotoRGB colour space.
Which colour space to use in your camera?
If you are shooting in Raw,-which you are highly recommended to do- it does not matter which colour space your camera is set to. You will apply the colour space when you are saving / exporting your images. However, if you are not shooting in Raw (e.g. in JPEG), and your images are meant for online sharing then you can use the sRGB. In anyhow, by shooting in JPEG you will reduce the number of colours embedded in your file (think about the bit-depth of a JPEG that we discussed in a previous blog). Therefore, make sure to shoot in Raw. You can always change the colour space to a smaller one like sRGB when exporting or saving a copy of your processed image. But you can not retrieve the colours you have lost during the shooting, due to the image format or a combination of a non-Raw format and a smaller colour space like sRGB.
Which Colour Space to use when sharing images online?
Currently most digital screens are capable of showing all colours of the sRGB space (or slightly more than that). But not all the AdobeRGB and certainly not those of the ProPhotoRGB colours. Hence, if your intention is to share your images online, the best colour space you can apply to your images is the sRGB. In this way you can predict how your images will look like when viewed on other screens (provided other screens are also calibrated). If you use larger colour spaces like AdobeRGB, then the device that is used to display your image will change the colour space to sRGB, and the colours that do not exist in sRGB will be changed to the closest colours that exist in the sRGB. Therefore, it is recommended to use the sRGB space for sharing your images online.
Which colour space to use when sending your images for printing?
As discussed above, printers use a different colour system to reproduce colours in your digital images, the CMY(K). When saving your images (in TIFF, or PSD formats) for print, the best option is to keep your images in AdobeRGB as it contains a larger colour space and very high end printers / print papers are able to closely reproduce those colours. Converting images to CMY(K) is generally not needed. But a conversation from the colour space of your digital image to the colour space of the printer is needed, which can be controlled best from photoshop and I will address it later on.
If you are sending your images to online print services, you need to follow the recommendations of those service providers regarding the format and the colour space of your images. Most of them will ask you to deliver your images in sRGB. Others may accept AdobeRGB or may ask you to convert the colour space of your images into the CMY(K). When changing the colour space, do this always on a copy of your original image. So, you can keep your original image in a wider colour space (i.e. AdobeRGB or ProPhotoRGB) for future use. This is important because future technologies will certainly bring monitors and printers with wider gamuts, and then your original files will come to a good use.
I hope this was helpful, should you have any question or remark please do not hesitate to send me a message.
Triangle Photo Academy Team
This article was prepared by Armin Armani