Through these pages, I will teach you the specific vocabulary linked to color management. As this is a quite new vocabulary, this is often not part of the well known vocabulary linked to argentic technics. Here, monitor calibration devices and ICC profiles replace tubes, chemical products and thermometers.
Key points if you are a beginner ...
Here are the key points to remember on color management. The rest of this page will be dedicated to those who want to go into more details.
Color management is a set of tools and concepts that try to preserve as much as possible, the same colors from the shooting to the final use : printing or Internet. All this to avoid those too often heard things : "Oh, the colors of my prints are very different from my monitor..." or "your colors are not like mine at home..." or even "Your monitor is dark !" and so on...
Color management thus serves to align all monitors, printers on the same color values, at least, close to it. The goal is for example to display a photo at home, a photographer place, or your neighbor with the same aspect ... For this, we will need to calibrate.
The basis of color management is constituted by the calibration of the different devices that we will be used and in the first place comes the monitor. The digital camera can be calibrated but only under certain conditions that cannot be of interested when starting. Then, remains to calibrate the printer.
But how calibration works ? Calibration is used to know and then neutralizing the defects of a monitor, for example so that it displays the "right" colors, or in other words, the correct colors and if possible very close to all other calibrated monitors. The uncalibrated monitor can therefore have many display defects that calibration will attempt to correct. Once calibrated, all monitors, all printers must be close enough to each other in terms of colors and most importantly, you must have the satisfaction of saying : "Great, my print and my photo displayed on the display are identical or, at least, very close to each other".
Color management : Here is a step that should not be neglected and yet is too often ignored by photographers and graphic designers, when they work their images on a computer. Yes, you will need proper tools - monitor calibrator or colorimeter, spectrophotometer, color target etc ... - to get a good color management but it is perhaps not that complicated ... This is just a little longer to explain than depth of field because there are many important concepts and new vocabulary. Indeed, none of our ancestors have told us about ICC profiles, gamut and Lab colors !
However, I hope to show you in the pages of this tutorial that color management is not reserved to some elite, but must be part of any photographer culture - amator or professional - just like focus, depth of field or light measurment. Color management with ICC profiles is the technical basis of our new laboratory, our digital laboratory where the colorimeter and color target have replaced our thermometers and tubes.
In the process of accurate nature color reproduction, photographers, even amators, who sometimes made significant investments in their digital camera equipment for its qualities, are often unpleasantly surprised to see that the colors displayed on the monitor and the print that comes out of their printer are significantly different ! From one step to another of his color workflow, colors change. Each device introduces its own "deformations" when it succeeds to reproduce the color ! It is quite painful, who should be believed ? Why ? Is my monitor or my printer right ? Who is right ? What and how to fix it ? These are questions that I have asked myself because I thought I was wasting a lot of paper and ink away, even though I had the feeling of getting a correct result at the end. The problem : each time I spent a lot of time on each print before being satisfied. In these pages on color management, I will try to provide some answers and explain how to control the color aspect of the images from one end to the other of the color workflow.
I address here all my warm thanks to Gerard Niemetzky and his team from Color-academy for their valuable advices during the first writing of this guide in 2004, and all those near and far people who have supported me. Since then, many others have helped me to develop it... So thank you all and enjoy your reading.
Color management problematic
In a perfect world (!), our eyes, our digital cameras etc... would all see the same colors ! In reality, for the photographer who works his images on a computer, it is quite different. But by the way, how many colors can the eye see ? How to go from one device to another with the same perceived colors ? How many different colors your monitor can really display ? And your printer able to print ? How to represent these colors with numbers ? What color distortions are introduced by a color reproduction device, even of high quality ? How to fix it ? Here is a sample of the questions that often arise when photographer works with digital devices ...
Color management tools are here to simplify your work and allow you to obtain a controlled result, during the processing of an image, from scanner or digital camera to inkjet or offset printing. Through the calibration of all the elements of the color workflow, as well as tools of our color management system - CMS - we may consider each device color defects to correct them and get a very high quality result throughout the processing flow of our photographs.
Tips to understand ...
Since the beginning of the last century, we know that the human eye sees the world through color-sensitive cells lining the back of his eye. It is noted that there are two broad categories: rods especially sensitive to the amount of light and cones sensitive to color but with a singular peculiarity : these cells are especially sensitive to Red, Green and Blue. So for almost a century, we know that the human eye can only see a few colors directly but rebuild all others in his brain by the mixture of these three so-called primary colors. Since man sees in RGB, engineers made computers, monitors, digital cameras or printers work on this principle. So each pixel in your camera sees colors in RGB. To an RGB value corresponds a color. It's very simple to understand and implement. But then, if for a given device, a given RGB value actually corresponds to a color, the same value is not strictly the same color for another device. An example to finally understand the problem when it comes to RGB : television. Even if they receive the same television program - so the same RGB signal - they do not all display the same colors !
The color model is based on the model of the human eye but takes us into a weird world where a given RGB signal does not only match a single color for everyone but multiple colors. Then, is there an absolute color model, one where the colors are not described by the RGB values but something absolute ? This model has been invented and called the Lab color model. Lab colors are absolute colors, for which a Lab value corresponds to one and only one color, that can be identified by its wavelength. The art of color management is to know, what RGB signal matches a given Lab color.
The core of color management is based on all colors actually perceived by a "standard" human eye that is to say Lab color. Indeed, Lab color corresponds to one and only one absolute color for this "standard" eye. The calibration of each device will allow to know what signal RGB or CMYK color corresponds to the unique Lab color, knowing the fact that no device does it in the same manner. To display a color - a Lab color - a monitor will have to display a given RGB signal and another monitor, even from the same brand, another RGB signal. To a Lab color corresponds several RGB colors and it is essential. So vice versa, a given RGB value represents a multitude of Lab colors depending on the device that will reproduce it. So it is just needed to translate each RGB value of a given equipment to Lab colors, when assigning an ICC profile before sending them to the next device through a conversion - which change the RGB value to another R'G'B' value - ... to print, display the same Lab color with a CMYK or RGB signal of its own.
In color management, it is not an RGB or CMYK info that is transmitted, paradoxically, even if so practical and directly based on the human eye way of working, because it is too dependent on the characteristics of a device, but a Lab color - unique - absolutely independent of any device, color perceived by a "standard" human being. An ICC profile contains the color characteristics of each device and is in charge of achieving this work of correspondence !
So, if your camera saw a red from the Lab colors, that "translates" it into its own RGB value, it will be possible to print this red, or a red from Lab colors perceived as close colorimetrically if not printable, thanks to the tools of color management - calibration, ICC profile creation, assigning ICC profiles, conversion, etc..
Color management and its ICC profiles creation tools therefore make possible to know a lot about a specific device : if this device can actually see, print or display a color and if it is technically possible for it, how does it do that ? So in other words, with which characteristics or "defects", does it do that ? Whether it is possible or not, the information is contained in an ICC profile, its ICC profile. To create it, a colorimeter, a spectrophotometer for printers and a color target for digital cameras are used. So, an ICC profile is the identity card of a digital device.
Quick summary of the color management guide
This guide on color management is divided into three parts : the basic concepts and vocabulary of color management, calibration of different devices - monitors or printers - and finally the setting up and use of ICC profiles with Photoshop.
Basic notions and vocabulary
Human eye and colors; computer science and colors;
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