Hi folks. As we know (or maybe we don't all know) many displays may change the appearance of the image on screen when you change your viewing angle relative to the display. Particularly troublesome is a laptop which 1) usually does not have a display that is resistant to such problems and 2) the viewing angle is highly variable simply because the screen is hinged and easily manipulated (or, worse yet, the screen moves all over the place when you are making your killer image edit with the laptop propped on your stomach while you are lying in bed 
).
While many folks eschew image editing on a laptop display, others use them every day and fairly effectively. I mean, you can throw a colorimeter on one, set your targets to something reasonable and get pretty good results. However, if you do not look at the display at the "correct" viewing angle (whatever that is - and how do you know?!) then the potential exists for getting radically different image appearance.
There is a really nice discussion about gamma over at Norman Koren's web page (Imatest Norman Koren) - in the discussion he provides a couple of test images to assess the gamma of your display. You may have seen these or similar images before - they are finely graduated line patterns that will typically merge into a flat gray area where your display's gamma resides. Here is the web address:
http://www.normankoren.com/makingfineprints1A.html
of the discussion and here is a screenshot of the image I am talking about - there is a second "Gamma 2.2" image below the one shown on the screen shot which is a similar assessment device.
Norman Koren's web site - gamma test image shown. Note that this is shown at full size, so the pattern is displaying properly here - is your display gamma correct?
After calibrating and profiling my laptop and my desktop display I realized that edits I was making on my laptop were a lot lighter in the shadows and quarter tones than on my Eizo desktop display. Both were targeted to 6500K, 90 cd/m2 and gamma 2.2. I figured maybe the black point of my desktop display was so much lower than that achievable by my late 2011 MacBook Pro, that that may have explained the differing and very obvious appearance of the darker tones between displays.
Turns out that was not the issue - after I experimented with various contrast ratios on my desktop display, I started to dig into the limitations of the laptop display. Turns out that viewing angle was altering the perceived (effective) gamma of the laptop display, making me see shadow and quarter tones on the laptop as lighter than a gamma of 2.2. So, when I would curve an image, for example, I was crushing the deepest blacks to compensate.
It is really startling to see just how much the display's effective gamma changes as a function of viewing angle. So, I needed a gauge of what viewing angle would actually give me the targeted gamma of 2.2. Enter Norman Koren's test images....
My MacBook Pro display pixel dimensions, 1680 x 1050.
The MacBook Pro (15") display is 1680 x 1050 pixels (contrary to the display properties screenshot, I use a matte display, not a glossy one - the effects discussed here are probably similar though). I normally use a plain, mid gray background for my desktop image. So, I thought, what if I could put the gamma test images from Norman Koren's web page on my desktop image - I could use my desktop image as a gauge of the correct viewing angle, knowing that the display should be showing me a "reading" of gamma 2.2 (my calibrated target).
So, in Photoshop, I made a new document that was 1680x1050, mid gray and then pasted the gamma test images into that document. It is really important that the image you make has the exact dimensions of your desktop so that the image is NOT scaled AT ALL when you apply it to your desktop - the gamma test images are very sensitive to pixel dimensions (see the screenshot of my desktop, which I scaled for purposes of posting here). Now, when I need to adjust my viewing angle, I can do it so that I get the gamma test images to indicate a gamma of 2.2, as they should.
Screen shot of my "Viewing Angle Indicator" desktop - note the distortion of the gamma test images due to resizing.
It is pretty surprising how far back from vertical (~30°) the display needs to be tilted to get the proper viewing angle when the laptop is on a desk and I am seated at a comfortable height. I suppose some ergonomist has determined this angle based on peoples' seated heights and what angle is required to make your viewing axis normal to the display. However, once positioned properly, I get good agreement between displays, when the images are able to be accommodated by both displays (e.g., sRGB images).
Anyway, I am probably not discovering anything new here, I am sure this has likely been done before (no I did not take the time to google it). Maybe this will help other laptop users control their displays - especially after spending time and money using a colorimeter to calibrate and profile.
have fun!
kirk
