Tag Archives: colour management

What colour is the sky on mars?

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mars_originalmars_red

The cameras never lies. Or does it? Recently I had to take a photo for a medical case and before submitting it I had to sign to say that the photo had not been modified. I did this – but it was ridiculous of course. Many people have this idea that the cameras faithfully captures what the scene looks like and that, unless we intentionally manipulate the images (in photoshop, for example), then we have captured the truth. Nothing could be further from the truth – as the recent image of #TheDress showed.

The top photo above was taken and released by NASA in 1976 and shows a Martian landscape. The sky is blue. However, at the time, Carl Sagan said “Despite the impression on these images, the sky is not blue…The sky is in fact pink.”

You see the original image had not been colour corrected. Colour correction is a process that takes place on most cameras these days without the user being aware of it but in 1976 was not automatic. The process can compensate for the spectral sensitivities of the camera sensors (which may differ from one camera to another) or for the colour of the light source. The second picture (above) shows the colour-corrected image. Some people are now arguing, however, that the amount of colour correction applied by NASA is wrong and that the sky should not be as red as it appears on the second photograph. For the full story including some other nice images of Mars see here.

3D colour printer

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An article in Stuff reveals what 3D Systems claims to be the world’s first continuous-tone full colour 3D plastic printer, called the ProJet 4500.The ProJet 4500 offers full-colour parts with colours that are able to blend into each other with gradient transitions.

MRes Colour Communication

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colour communication

We’re starting a new programme at Leeds University next September. It’s MRes Colour Communication. This is a one-year Masters programme by research but with a twist. There is a taught component in the first semester to get everyone up to speed to make sure they understand the basics of colour communication. They then explore one aspect of this in their research project and submit a dissertation at the end of the year. Please contact me at my University email of s.westland@leeds.ac.uk for further information or visit http://www.design.leeds.ac.uk/pg/research-degrees/.

swatchmate

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Very interested in this new colour-measurement device called the swatchmate cube.

swatchcube-color-matcher-designboom03

The new device is launched by Swatchmate on November 13th. That;s two day’s time from now. It captures the colour and displays it on your smartphone. Does it provide any numerical data such as CIELAB? I don’t know. How much is it? I don’t know. I guess we’ll find out at the launch!!

colour management for beginners

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Colour displays are now affordable and enjoyed by consumers at work, at home, on mobile displays and in cinemas. Consumers often take it for granted that there is good colour fidelity as images are transferred between different devices. So, for example, a red object in an image appears to be approximately the same red when the image is displayed on different computer displays, when it is printed, and when it is viewed on a mobile phone.

This colour fidelity is not easy to achieve. Different devices use very different technology to display colour images. For example, a computer display will mix together light from three primaries (red, green and blue) to generate a range (gamut) of colours. On the other hand, a printer uses completely different technology and typically uses mixtures of cyan, magenta, yellow and black inks to create the gamut of colours. Even computer monitors use a variety of different technologies (from CRT displays, which are becoming obsolete, to LCD, LED, and plasma technologies) each of which may use quite different red, green and blue primaries. Colour management is required to compensate for differences between the technologies (colour primaries, colour mixing, colour gamuts) between different image-display devices. This necessitates that the companies that produce image-display devices must cooperate so that the devices are able to talk to each other; this is achieved through the International Color Consortium (ICC) . The ICC is an industry consortium that was established in 1993 by eight industry vendors (including Microsoft and Apple). Today approximately 70 companies are members of the ICC whose goals are to “create, promote and encourage evolution of an open, vendor-neutral, cross-platform colour management system architecture and components”. The ICC system is implemented in terms of device profiles and colour management system. The device profile is a computer file that is associated with each device (printer, camera, monitor, etc.) that essentially contains information to allow colour to be managed. In the case of a computer monitor, for example, the device profile would include information about the monitor’s primaries that would allow the colour image to be adjusted to compensate for the properties of the monitor so that the colours are displayed correctly. The colour management system is software that manages how these device profiles interact with each other and is normally part of the operating system of the computer.

Thus, when users capture, view, or print images they are using colour management all the time even though they may be unaware of it. Though this level of colour management is built into software and device drivers and is broadly invisible to the user it does enable colour consistency for images when they are captured, viewed and printed throughout the world. However, this level of default colour management is far from perfect. It does not, for example, generally account for changes in settings for a device (for example, a user may change the contrast, brightness, or colour temperature of a display) so that colour fidelity is, in practice, only approximate. This level of colour fidelity is probably sufficient to satisfy about 90% or more of consumers for whom colour is not a critical issue. However, for professionals working in industries where colour is a major concern (e.g. design, retailing) a higher level of colour management is often required. For these users, it is possible to obtain systems (typically low-cost colour-measurement devices and associated software) that allow a user-defined profile to be generated for a particular device with particular settings. This user-defined profile then over-rides the default profile and should enable a better level of colour fidelity to be achieved. Nevertheless, colour fidelity is always likely to be an imperfect issue. It is difficult for colour-management systems to perfectly compensate for the fact that, for example, different devices may generate quite different colour gamuts (typically, the bright red on a computer screen cannot be achieved by a CMYK consumer-level printer).

For ICC see www.color.org

adobe photoshop colour management

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Now, before I write anything thing, I should say that I am a big fan of Adobe products. And it’s hard to think of a company that has done more to progress colour management than Adobe. At the Leeds University’s School of Design, where I teach, we use many Adobe products and Photoshop and Illustrator are virtually standards in their respective fields.

However, I don;t like the way Adobe presents its colour management options.

Colour management is difficult and certainly imperfect. For those users who don’t know or care about colour management the efforts of companies like Adobe and many others (especially those that constitute the ICC – http://www.color.org/index.xalter) have made colour fidelity much better over the last couple of decades. Open source profiles and the use of, for example, the sRGB colour space have ensured that even for users that don’t care or know about colour management, things pretty much work ok. And for those that are experts and know the difference between an input gamut and an output gamut; well, the colour management facilities provided by Adobe, for example, in Photoshop provide excellent tools and resources.

But I can’t help thinking that there is a huge gap between the naieve user and the expert user. Most of the design students in our school, for example, are not colour-management experts but, then, neither are they naieve users. However, the way that most software is designed (and this is not specific to Adobe, to be honest) is that it’s either all or nothing. As soon as you click on colour management options you are presented with a huge range of options (working spaces, rendering intends, colour temperatures, etc.). It just seems to me that this presents the user with a bit of knowledge with a problem since by fiddling with these settings they are more than likely to make things worse rather than better.

If I ruled the universe, then I would have software that is adaptive – that is, it would present colour management options in levels. It would be great if the software could work out your level of colour knowledge and present options accordingly; but if this is too difficult – or unpopular – then at least it could provide a number of levels: naieve, casual, knowledgeable and expert, for example. This way, users would be presented with an appropriate array and range of options.

As it is, I can’t help thinking that the software writers enjoy showing as many options as possible – as if they are shouting,  “Look how many features we have!”  – without regard for whether it is helpful to the user.

What is a colour space?

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In my job I probably use the phrase “colour space” every day and have done for the last 20 years. So imagine my surprise when I was talking with a colleague recently and after a few minutes he said “Can I stop you for a second there Steve – when you say colour space, what exactly do you mean?”.

A colour space is like a map. A map of New York, for example, shows the location of various landmarks with reference to the xy coordinates (the position in horizontal x and vertical y units on the map). A colour space or colour map does the same thing with colours. Perhaps the simplest colour space is the spectrum, see below:
 myspectrum

As we look from right to left on the spectrum the wavelengths changes from around 700nm on the far left to about 400nm on the far right. So this map shows colour with reference to wavelength. Although it is a commonly used colour space it is limited because it only really describes how hue changes with wavelength. Hue is only one of three ways in which colour can change or vary.

The most well-known really useful colour space then is the CIE chromaticity diagram – see below.

chromdiagram

The CIE chromaticity diagram shows colours arranged on a 2-D plane. We can easily refer to any colour by how far from the left it is (the x coordinate) and how far from the bottom it is (the y coordinate). This space only shows two of the dimensions of colour; the hues are arranged in a somewhat circular way and the colourfulness increases as we move outwards from the white point (a position near to the centre of the diagram). However, we can also consider the third component of colour (brightness) if we imagine a dimension coming out of the page towards you (http://colourware.wordpress.com/2009/07/18/cie-system-of-colorimetry/). The CIE defines several different colour spaces; the CIELAB colour space, for example, is another 3-D space that defines a colour by its L*, a* and b* values.

It is useful to think of an image-display device as also having a colour space. Consider the display on which you are probably reading this blog. The display shows colour by changing the amount of the red, green and blue light emitted at each point on the screen. The diagram below is a representation of what the RGB colour space of your display device may look like.

 

rgb

In the RGB cube, black is in the bottom left. As the RGB values increase colours are created and white results from each of the RGB primaries at full strength. So the RGB colour space defines the relationship between RGB values and colour. However, here’s the really interesting thing: The colour space for different display devices is very different. Even if we take a single device – such as the one that you are reading this blog on – then as we change settings (the brightness, the contrast, the gamma, the colour temperature, etc.) then the colour space changes. That is, the relationship between RGB and colour changes as you change those settings. This is a huge problem. Imagine if there were many maps of New York and each showed the position of, say, the Empire State Building to be in a different position. How confusing would that be? Well, that’s the problem with colour-display technology. If we didn’t do anything about this problem then every time we looked at a colour image on a different display device the colours could change markedly. This is why we need colour management. Colour management can make compensations to the RGB values that are sent to each display device so that the colours always appear the same (well, nearly the same). To make this compensation the colour management software (which is embedded in your Windows or Apple operating system) needs to know about the colour space of each device connected to the computer. Each device needs to have a profile that describes the relationship of its own colour space with respect to some standard colour space. 

How good is colour management? Well, that depends upon many factors. Most printers, cameras, scanners, and screens (LCD, CRT, etc.) come with a driver that includes a crude colour profile. This ensures that there is a basic level of colour management and for a great majority of users this is more than adequate. However, if you want better performance then you need to think about making some measurements that will allow a more accurate colour profile to be built. In a recent blog I described a new device that you can buy to enable you to do this – http://colourware.wordpress.com/2009/07/29/colormunki-colour-management/. There are many such devices on the market. I highly recommend Andrew Rodney’s book Color Management for Photographers which is both clear and accurate (though the edition I have works on Adobe’s CS2 package whereas the latest package is CS4).

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However, no matter how hard you try, colour management is never likely to be perfect. This is because different devices have different colour gamuts; a printer is likely to be able to display some colours that your display physically cannot and vice versa.

colormunki colour management

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Colour management is needed to try to ensure that when using computer systems colour fidelity is achieved across different machines and between soft and hard copy. Computers represent colour as three numbers, RGB. But the same RGB values displayed on different monitors will usually result in a different on-screen colour. In addition, there could be colour gamut issues; one monitor may be able to display colours that are simply out of the achievable range of another. When we consider printers the problem is even worse. The gamut of a printer is very different to that of a computer display. And printers tend to represent colour in terms of CMY or CMYK values. So the colour-management software has rather a lot to do to satisfy users.

A great deal of colour management goes on in computer systems of which the average user is completely unaware. This uses default settings and makes various assumptions but is normally good enough so that reds appear red and blues appear blue on any computer display or printer. Colour management has been built in to Apple software for a long while and is now also part of the Microsoft operating system. But the professional user may require more than is offered by the basic colour management that comes as part of all new systems. However, professional-level colour management comes at a cost and it’s not just financial. It is usually necessary to have to characterize each device (monitor display, printer etc.) that is to be used; and this requires colour measurment and some knowledge of colorimetry.

I recently came across a new product – ColorMunki 1.1 – released by X-rite that promises enhanced colour performance for colour-critical users. This seems to be an interesting product in that it is aimed at designers and photographers.

ColorMunk 1.1 – http://www.colormunki.com/ – is in fact a suite of software that also include a device for measuring colour. I am looking forward to trying this out. If anyone has any experience of this system that they would like to share it would be vey helpful.