I have a confession, I’ve never really got why you should compensate for ambient light when calibrating and profiling monitors. Don’t get me wrong I understand the principles and the effect that ambient light can have on the images you see on your screen, it’s just that to me making your monitor brighter or darker based on the light surrounding it is the wrong way round. Isn’t it better to get your ambient lighting to the right level so the monitor looks its best?
My first experience of colour correction came when I was working in a pre-press company and our drum scanning suite was housed in a former funeral parlour. Windows were few and far between and you can imagine that the lighting was on the sepulchral side, especially during the night shift. My current office has a large window but as soon as I do any image correction or software testing down comes the venetian blind to make the lighting as dim as I can. When I go on site to retouchers or video editing suites the light is also very low. My standard advice is that if the monitor is the brightest light source then your eyes will adjust to it correctly. Some customers say they haven’t got control over ambient light and I can imagine that in an office environment but for all our amateur customers most spare room digital photo studios are surely equipped with a light switch and a set of curtains.
I think the problem is that I know enough about monitors and print viewing to know not to hold a print next to my screen and expect it to match exactly. If I want to get closer agreement between the two I break out the viewing booth and adjust my monitor calibration targets to get a visual match but I usually take my prints to the window and view them in daylight and I find when I allow my eyes to adjust properly to either daylight or the monitor then what I see on screen is close enough to what I get out of the printer. So my only aim for the ambient lighting around my monitor is for it to be dim enough for me to see all the details in my images, especially in the shadows, so for that the room lighting has to be very dim.
Anyway, I’ve just started beta testing a new monitor calibration solution and amongst the first few screens in the software is the ability to measure ambient light and adjust the calibration targets accordingly. The developers were making a big song and dance about it so I thought I better revisit the area of ambient light compensation to see if I was missing something.
Our biggest selling monitor calibration and profiling solution is the i1 Display 2 from X-Rite. It’s philosophy dove tails with my own view on ambient lighting in that it does allow the measuring of ambient light but it is for information only and doesn’t suggest calibration targets, affect the calibration or monitor ambient light and adjust the monitor on an ongoing basis.
I connected my i1 Display 2 and launched i1 Match. I checked the Ambient Light Check option and then closed my blinds as I usually do when I work on images. I clicked measure and found that at 28 lux it thought my lighting was too dim so I opened the blades on the blind slightly and remeasured until the black line was in the central green area. The room was still acceptably dim but not quite as dark at 53 lux. After calibrating the monitor to 120cd/m2, 2.2 and 6500K (my usual targets) I examined my Square Black Level Test image that has concentric areas of very low RGB values. I could not see much variation in the blacks but if I closed the blinds completely again then I could see all the values distinctly. The recommended values for ambient light in the i1 Match software are based on the ISO 3664 standard although another ISO standard, ISO 12646, recommends lower levels of light, such as I normally have.
The Spyder3 Elite software does have more ambient lighting features. During the calibration process it can measure the ambient light and suggest new calibration targets. The Spyder Utility can also be set to monitor ambient light and warn you if it begins to differ too greatly. The first half of this article was written in the late afternoon when the sun had gone around the side of our building. This second half on the Spyder I’m writing in the morning with the spring sun shining on the window. I have the blind fully closed but it is still much brighter than yesterday, i1 Match says 182 Lux.
Running the ambient light analysis as I calibrate the monitor using Spyder3 Elite it suggests a luminance level of 200cd/m2 and that is much higher than my normal 120cd/m2 target. It reports the lighting level as Very High. It is brighter than yesterday but I wouldn’t really say it was very bright, it’s still dimmer than most offices. I accepted the Spyder’s recommendation and calibrated the monitor. It was much brighter than I’m used too and looking at images in Photoshop both before and after I preferred my normal luminance level. I couldn’t see the shadow detail on my Square Black Level Test image even with the monitor set brighter than normal. I turned on the ambient light monitoring in the Spyder utility and after a short while the little icon turned red and when I went into the utility it said the ambient lighting was now just High and I should recalibrate or return the ambient lighting to the condition it was when I calibrated. I hadn’t opened the blind or anything, the sun must have gone in or moved around the building a little.
If I was a photographer wanting to process some RAW images I would now have the quandary of wondering wether to wait for a cloudy day, recalibrate every time the weather changes or, I suppose, buy a proper black-out blind.
Constant recalibration would mean the images I see on my monitor would always be changing and I think I still prefer to stick to the same calibration targets over time. Obviously you can’t always choose when you process your files. So, of the three choices the black-out blind makes the most sense to me. If you can block all light coming in from outside you could control the lighting level more precisely, all though of course you’d have to choose any artificial lighting carefully for the intensity, colour temperature and colour rendering index. Many of us started our photography by working in a darkroom and I think for many it still makes sense to work in one now.