Color Management
references:www.cambridgeincolour.com -tutorials-colormanagement
(a series of 6 tutorials covering many aspects of color management)
www.lynda.com -colormanagement
What is color management?- Achieving consistency and predictability between multiple devices.
Input devices, such as cameras and scanners, working devices, such as computer monitors and output devices such as printers.
We have first our input devices, our cameras and scanners our display device, our computer monitors and our output devices namely our printers.
Our input and monitoring devices live mainly in the realm of the RGB color space Why?
RGB is a system based on light.
Our output devices are dependant on the CMYK color space. Why?
Because colors in a printer are dependant on inks and the colors of printer inks are Cyan, Magenta, Yellow and Black.
Color reproduction has a problem in that a given color number doesn’t always produce the same color in all devices
1) Every device gets a profile
Various methods are used to create device profiles that describe to all other devices what its characteristics are. Monitor profiles describe what colours are produced when RGB values are sent to the monitor. Printer profiles describe what colours are produced when RGB values are printed. Scanner profiles describe what RGB values are created when colours are scanned.
2) We work in device independent colour spaces We use an device independent colour space to insure that all users use and see the same colours on their various systems. The monitor profile is used to correct the information we see on the monitor so that images displayed in a common device independent colour space will all look the same. Device independent colour spaces have names like AdobeRGB, sRGB, ProphotoRGB, etc..
3) Different colour spaces display more or less of the visible spectrum.
It’s preferable that a device independent colourspace include all the colours that an output devices can reproduce while avoiding colours that cannot. Device independent colourspaces are often referred to as being a large colourspace or a small colour space depending on how much of the visible spectrum can be represented. AdobeRGB is a medium sized colourspace. sRGB is snaller and has become a standard for most consumer printers, digital cameras, etc.. Using a larger colourspace will enable a file address a wider variety of output (offset presses, film recorders, specialized inkjet printers). But if you typically print to sRGB targeted devices that cannot reproduce many of the colours displayed on your screen then it’s recommended you do final colour corrections in that colourspace. Many portrait and wedding photographers find an sRGB workflow to be more problem free.
4) Different colourspaces define colours differently. RGB images displayed on a monitor are made up of 256 levels (0-255) each of Red Green and Blue. Colours are defined by RGB values such as 128R, 57G, 210B and these values are what defines different colours. Colours with the identical numerical values will be different according to what colourspace it is in. Unless we know what colourspace is associated with the image, the RGB colour values in the image will have no meaning. Images displayed in the wrong colourspace will display incorrect colours.
Images can be CONVERTED to other colourspaces and new corrected values are assigned to the image. You can easily convert (re-map) a smaller colourspace image to a larger one without any loss. You can NOT convert a larger colourspace image to a smaller one without losing colours that do not exist in the smaller colourspace. The bigger the difference between the two the more potential there is for loss. The only similarity shared by between colourspaces is that all colours that have equal RGB values will be neutral (a shade of neutral gray).
5) You must respect the colourspace. When you open an image it is preferable that you work in the colourspace of the original.
A typical colour managed workflow
1) Insure that the monitor is calibrated properly (preferably using a hardware monitor calibration device).
2) Open the image and choose to Use the embedded profile if you are prompted that the embedded profile is different from your default working colourspace. In our case, at Dawson, your profile should have been saved in the Color Sync utility
3) To print the image-at Dawson Follow the directions attached to the printer.
At a commercial lab- Most labs use equipment’s default colour management settings which are set to reproduce an sRGB colourspace correctly. This is because the colourspace of all consumer digital cameras is sRGB. There is little to gain by sending your images in a different colourspace unless a lab is using custom settings that make use of a larger colourspace and are equipped to recognize embedded colour profiles. This is usually done my pro labs only and even many of them use an sRGB workflow. You risk having the colours reproduced incorrectly from labs that do not expect anything other than sRGB files. It’s simply safer to convert to sRGB and know that there is much less risk of things going wrong.
NOTE: Colour Management is NOT a perfect science !
The role of colour management is to enable us to get colours to reproduce as accurately as possible on different devices such as monitors, digital cameras, printers, scanners and film recorders. There are many variables that can affect the accuracy of the results so you should not expect perfection. But you CAN expect results to be very close and with a few small adjustments you should be able to produce as high a quality as a device is capable of.
- Measuring instruments accuracy depends on their quality.
- Viewing accuracy depends on the quality of the monitor.
-Output quality depends on the quality of the printer and the accuracy of the viewing light source. The printer can only reproduce a specific gamut of colours so there will be colours in almost every device independent colourspace that cannot be reproduced.
