Using Your Camera To Check Monitor Luminance And Print
One of the most common complaints that we hear about matching the print to the
monitor is that the prints are too dark compared with the image on the monitor.
Often, the fault is not with the
print but with the monitor luminance (brightness). If the monitor is too bright,
you will invariably reduce the image brightness to make it look "right". Result
- genuinely dark prints.
Another common cause is that even if the monitor luminance is
correct, the prints are viewed with low illumination. To get the most from a
print you will need a fairly high level of illumination; in poor light the
shadow detail will be lost, giving the impression that the print is too dark
To realistically compare the printed image with the monitor image
it is necessary to make the perceived brightness of the print match that of the
monitor. This means viewing the print with a light level of at least 500 lux -
the kind of level normally found in a brightly lit office or supermarket. The
level in a typical living room may be as low as 50 lux, so you cannot expect to
see your prints at their best while sitting in your armchair.
Few photographers have the special equipment needed to measure
both monitor luminance and illuminance of the print viewing area. However, every
photographer has a camera, and a good camera can do this job with an accuracy
much better than you can do with your unaided eyes. Try the simple procedure
Checking monitor luminance
The factory settings for modern LCD monitors are always far too bright for photo
editing; so, unless you use a hardware calibrator to set luminance, it is
worthwhile spending a few minutes to check that you are at least in the right
ball-park. A good quality camera will allow you to do this.
If you are reasonably confident that your camera gives correct exposure, follow
this procedure to check or set your monitor luminance.
Naturally, this procedure will not guarantee you a precise
measurement of luminance, but it is at least objective. We have no innate
reference for luminance so any measurement technique is probably better than
doing it by eye.
||In your image editing application, open a new, blank document with a
white background. Open this document in full-screen mode so that most of
the screen is filled with white.
||Set your camera to manual focus and set the focus to infinity. Do
not use a close focus mode because this will change the effective
aperture of the lens and your readings will be inaccurate.
||Set your camera as follows: ISO 400; Aperture Priority; f/5.6
||Point your camera at the centre of the screen at
close range (50cm or less) so that the viewfinder is completely filled with white. Don't
worry that the image is completely out of focus - it will not affect the
exposure reading. In fact, you should find that moving the camera back
and forth between 20cm and 50cm does not affect the exposure reading.
||Note the exposure reading. This will normally be displayed as a
fraction of a second - in other words, 1/60th
will be displayed simply as 60. This displayed number will be
(approximately) the luminance of
your monitor in candelas per square metre (cd/m2)
||The recommended luminance for photo editing is 120 cd/m2 so you
should adjust your monitor brightness to get an exposure reading of
between 100 and 125. (1/100th to
Note: The light from LCD
monitors is polarised, and this will have an effect on SLR metering systems. If
you use an SLR to check an LCD monitor, take one reading with the the camera in
the landscape (horizontal) orientation and one in portrait (vertical)
orientation. The difference will probably be 1/3 to 1/2 a stop. The higher
reading will be the more accurate.
For some monitors the lowest achievable luminance will be
higher than 120cd/m2; the iMac is one well known
example of this. If your monitor cannot be set to 120cd/m2
don't be tempted to use one of the software methods to reduce the luminance.
These methods usually reduce the number of colours that you can display, and may
well produce colour banding where smooth colour gradients have visible steps.
Better to live with the higher luminance and adjust to it mentally!
Checking illuminance of print viewing area
the illuminance of the print viewing area can be done in a very similar way to
that used for checking monitor luminance. Follow all the steps above, but in
step 4, instead of pointing your camera at the monitor, point it at a sheet of
matt white paper in your print viewing area. Ordinary copier paper is perfectly
adequate for this job.
Fortunately, you are not too
concerned with the actual lux level. All you need to do is to make sure that the
exposure reading is the same, or higher, than the reading you obtained from the
monitor. You can then be sure that the print luminance is similar to that of the
As a very rough guide, a desk lamp with a 60W
bulb (or low-energy equivalent) will give the right illuminance at about 50cm
(18 inches) from the print.
Exhibition prints or armchair prints?
A custom printer profile will generally give the best possible
prints from your printer. That means the most accurate colour and the widest
range of tones. Unfortunately, "perfect" exhibition prints may not look right in
poor lighting. You may therefore decide that you prefer lighter prints for
day-to-day "family" viewing.
If you decide to do this,
then a simple "Levels" or "Curves" adjustment in your image editing application
can be applied just before you print the image. Be aware though, that although
the colours will still look natural, your lightened prints will probably look a
bit washed-out in exhibition level lighting.