Monitor Calibration

The first step in any color management system for the digital artist should be monitor calibration. What we strive for is an acurrate RGB representation on screen of the digital image file. Before we can even get reasonably close to a WYSIWYG (What you see is what you get) environment we have to know that the screen is displaying the best possible color for a given RGB pixel value. All monitors display images in an additive color space using a 3 channel RGB model. Every color in screen is defined by adding red, green and blue values to get a final discreet color. The maximum value in a given channel is 255, thus white becomes: R=255,G=255,B=255 and Black is :R=0,G=0,B=0. The actual colors displayed on screen however depend a great deal on the state of the phosphers, the warmth of the electron guns, the age of the components, ect... Monitors vary widely accordingly and calibration becomes crucial. How does one calibrate, what should the monitor colors look like and how do we match what we see on screen to what we get on output ?

Most new artists start with the Adobe Gamma control panel supplied with Adobe Photoshop. This is the poor mans calibrator and although hardware calibrators can be invaluable the lowly Gamma control panel is not without its advantages.The newest version of this utility has a helpful wizard interface with some modest improvements over the older version. The wizard walks you through the calibration proceedure alowing you to visually calibrate your display to a reasonable state. I advise going through the wizard first to get a feel for how the control panel works.After you've used the wizard you can skip to the regular control panel by checking the radio button for the control panel at the opening screen.

The control panel allows you to set a desired gamma ( look under the color patches- I always use 2.2 ) and has two bars of black and white that let you verify the contrast and brightness setting of you monitor.( adjust your monitor until you can just barely see the checkerboard pattern in the black bar and keep the white bar white ) The hardware white point can be visually estimated by clicking on the measure button and selecting the most neutral looking gray patch in the following windows. I generally select a white point of 5500 rather than the so-called proofing standard of 5000 because it seems to look more neutral on most systems. The basic color adjustment procedure involves moving the sliders under the red, green and blue squares until the inner square matches the brightness of the outer region. Sometimes it is helpfull if you check the "view Single Gamma Only" check box and set the over all gamma first- then return to the three color sliders to fine tune the color. If you squint your eyes a bit it becomes fairly easy to set the red and green patches. The blue is always harder because it requires large movements to see any difference at all. Basically, you should set the red and green and then use the blue to determine the warmth or coolness of a neutral tone. It helps greatly to have some other referance for neutral gray on screen when you do this. At the very least you should be using a gray desktop! ( I know, a flat gray desktop is boring but you can use some kind of textured desktop as long as it's completely neutral.) It's also very nice if you can have an image with known values in it to display while you are using the Gamma control panel. I have built such an image for your use and you can download it in the download area along with some other useful calibration files. ( you can also download it immediately if you want )

This is a 600x800 pixel RGB file that is ideal for 17" and larger monitors. I supply it here in an LZW Tiff format to avoid any compression artifacts and make it accessible to other platforms besides Macintosh OS. This image was made to accomodate the older Gamma control panal and there is an area in the image where you can place that smaller control panel window so as not to obscure the important features of the image. The older control panel works just as well and it takes up less screen space so in many ways I like it better. If you still have a copy you can go ahead and use it the way it is illustrated here. Otherwise use the new one and position it so that it doesn't block the gray ramps and you can still see the womans face. I will be giving directions here for the Macintosh OS, PC users will have to adapt the steps to suite their situation Make sure you have unchecked the hide desktop when in background option in the general control panel because you want to be able to see the image as it is displayed behind the control panel. Ideally, if you can get a good output, you will want a transparency output of this file for reference while you are calibrating (8x10 is best)- an LVT output or the equivalent has the same RGB colorspace (although with a wider dynamic range) as the monitor and it can provide a good visual reference for what the RGB file looks like. You will also want to wait before calibrating until your monitor has warmed up for at least an hour.RGB calibration ImageOpen the calibration image in Photoshop - VERY IMPORTANT - make sure you uncheck "Display using Monitor compensation" in Photoshop's RGB setup; you don't want Photoshop to be adjusting the image for your working space while you are trying to calibrate the monitor. Once the image is open into an un-adjusted state open the Gamma control panel. You can now begin to tweak the controls while you have the image in the background to look at. If you have a transparency output keep it handy for reference. Make sure you can view it with a 5000° kelvin light source for acuracy. Many people use a small commercial viewing booth next to the monitor- this is quite a luxury and these units are available from pre-press supply sources. Typically, you will have to warm up the image quite a bit by sliding blue to the left, keep checking your referance transparency and especially look at the gray values in the image. You should just barely be able to discern a separation between the two lowest values in the gray step on the right of the image at a gamma of 2.2. You might have to adjust the brightness of your monitor to show the separation in tone. The white point is also important- most people have their white set too blue, if you are viewing your referance transparency with the appropriate light source (5000° kelvin) you will notice that white is actually quite yellow compared to the normal monitor color. Once you are done you can save the settings and create a monitor profile by closing the control panel window, click save in the resulting dialog, name the profile and if you have a multi-monitor setup, re-launch the control panel, move it to the other monitor and repeat the procedure for that monitor . Re-adjust your calibration at least once a week as monitors, especially older ones tend to drift over time. The more you work with this image the better your calibration will become. Consistency is the key, by always working with the same image you can learn to see subtle shifts and correct for them. Feel free to substitue an image of your choice for the headshot in this calibration image or make one up yourself, just be sure you can get a good output of the file for reference and you have some known values in it. This particular image has other uses that I will go into in other tutorials.

Now that your RGB monitor is calibrated go back and re-check "Display using Monitor compensation" in Photoshop's RGB setup. The Gamma control panel can be very usefull in a number of situations. When you are evaluating an image for transparency output it is a good idea to open the Gamma control panel and change the gamma to 1.4 or even 1.0,temporarily ( don't close the control panel or save the profile ) opening up the gamma to check for defects in the shadow areas ! The reason this is critical is that transparencies have a much wider dynamic range and you can see into the shadows more- you can get some nasty surprises when you output files without checking shadow detail in this manner ! In general, for overall viewing and color correcting, you should use a gamma of 2.2 for your monitor. There is some debate in this area but Photoshop will adjust your display to simulate as much as possible what a given file looks like in the workspace you have chosen and using a gamma of 2.2 on your monitor allows for more "bits" of data in the "clut" for the lower values (shadow detail) that the eye is more sensitive to.

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