[oldSettings,errorMsg] = MacDisplaySettings([screenNumber,][newSettings])

% MacDisplaySettings allows you to peek and poke seven settings in the
System Preferences:Displays panel by using the corresponding fields in
its newSettings and oldSettings input-output arguments. This allows you
to temporarily override any macOS user customization of the your
display, to allow calibration and user testing with stable display
settings. (To be clear, we help you handle the macOS built-in System
Preferences; we do nothing about the zillion third-party apps that your
users might install.) All the parameters refer only to the screen
selected by screenNumber. However, Apple has very limited support for
non-Apple displays, so you probably won’t have Brightness, True Tone, or
Night Shift on your external display unless it’s made by Apple. The Color
Profile options seems to always be available for all displays.

brightness the Brightness slider
automatically the “Automatically adjust brightness” checkbox
trueTone the “True Tone” checkbox
showProfilesForThisDisplayOnly the checkbox
profile name of selection in Color Profile menu
profileRow row # of selection in Color Profile menu
nightShiftSchedule the Night Shift Schedule pop up menu
nightShiftManual the Night Shift Manual checkbox

% INPUT ARGS. Both arguments are optional: the integer screenNumber
and the struct newSettings. You can provide either, neither, or both.
It’s ok to provide just “newSettings”, omitting the “screenNumber”
(default is 0, the main screen). The struct “newSettings” can include
any number, from none to all, of the eight allowed fields:

“brightness” (in the range 0.0 to 1.0)
“automatically” (true or false)
“trueTone” (true or false)
“nightShiftSchedule” (‘Off’,’Custom’, or ‘Sunset to Sunrise’)
“nighShiftManual” (true or false)
“showProfilesForThisDisplayOnly” (true or false)
“profile” (text)
“profileRow” (integer)

If newSettings.profileRow is specified then newSettings.profile is
ignored. True Tone is not available on Macs manufactured before 2018.

% OUTPUT ARGS: The struct oldSettings uses the fields listed above to
report the prior state of all available parameters. errorMsg is a second,
optional, output argument. If everything worked then errorMsg is an empty
string. Otherwise it will describe one failure, even if there were
several. In peeking, the fields corresponding to a parameter that could
not be read will be empty [], and that is not considered an error. In
poking, if you got an error, you might call MacDisplaySettings again to
compare the new peek with what you poked.

% EXAMPLES. Typical uses of MacDisplaySettings include just typing the
function name to learn the current settings:


ans =

struct with fields:

                     brightness: 0.8700  
                  automatically: 0  
                       trueTone: []  
             nightShiftSchedule: 'Off'  
               nightShiftManual: 0  
 showProfilesForThisDisplayOnly: 0  
                        profile: 'Color LCD'  
                     profileRow: 1  

% In one call to MacDisplaySettings you can both peek the old settings
% and poke new settings.

newSettings.profile=’Display P3’; % Select Profile by name.
newSettings.profileRow=1; % Specify Profile row, and ignore “profile” field.


% Now use the display, and then restore the old settings as you found
% them. You can omit “screen” if you’re working on the main screen (0).


% PRESERVING THE DISPLAY STATE. Apple invites Macintosh users to adjust
many parameters in the System Preferences Displays panel to customize
their display color and brightness including the enabling of dynamic
adjustments of all displayed images in response to personal preference,
ambient lighting, and time of day. Many users enjoy this, but, unless
reliably overriden, those adjustments defeat our efforts to calibrate the
display one day and, at a later date, use our calibrations to reliably
present an accurately specified stimulus. MacDisplaySettings aims to
satisfy everyone, by allowing your calibration and test programs to use
the computer in a fixed state, unaffected by individual user whims,
ambient lighting, and time of day, while saving and later restoring
whatever custom states the users have selected. MacDisplaySettings
reports and controls seven settings. It allows you to read their current
state, set them to standard values for your critical work, and, when
you’re done, restore them to their original values.

% ERROR REPORTING. If everything worked the optional output argument
errorMsg is an empty string. Otherwise errorMsg will contain an error
message string, just one even if there are mutiple faults.

% ERROR CHECKING. Most of the controls are straightforward, you are just
peeking and poking a Boolean (0 or 1) or a small integer with a known
range. Brightness and Profile are more subtle, so MacDisplaySettings
always checks by peeking immediately after poking Brightness or Profile
(whether by name or by row). A discrepancy will be flagged by a nonempty
string in errorMsg. Note that you provide a float to Brightness but
within the macOS it’s quantized to roughly 18-bit precision. In my
testing on a MacBook and a MacBook Pro, poking random numbers between 0.0
and 1.0, the discrepancy between peek and poke is uniformly distributed
over the range -5e-6 to +5e-6, provided you wait at least 0.1 s after the
latest poke. (When you move the slider, the macOS does a slow fade to the
new value.) For MacDisplaySettings’s built-in peek-after-poke test,
MacDisplaySettings accepts the peek of Brightness if it is within 0.001
of what we poked, otherwise it waits 0.1 s and peeks again, and if the
second peek is still out of range, then reports the discrepancy in

% RELIABLE. MacDisplaySettings is fast (2 s) and reliable, unlike my
previous efforts (AutoBrightness. The
improvement results from discovering, first, that the applescript
operations proceed MUCH more quickly while System Preferences is
frontmost (so we now bring it to the front), and, second, we now follow
the example of pros and have wait loops in the applescript to make sure
each object is available before accessing it. Since those enhancements,
it now reliably takes 2 s, instead of the long 60 s delays, and
occasional timeout errors, that afflicted the old routines.

% INPUT ARGUMENT RANGE. newSettings.brightness has range 0.0 to 1.0;
automatically, trueTone, nightShiftManual, and
showProfilesForThisDisplayOnly are boolean (true or false);
nightShiftSchedule is a text field corresponding to any of the items in
the Displays pop up menu (‘Off’, ‘Custom’, ‘Sunset to Sunrise’).
(nightShiftSchedule is compatible with international systems, provided
you use the English field names when calling MacDisplaySettings.m.)
profile (text) specifies the desired Color Profile by name, and
profileRow (integer) specifies it by row. The row number will work
internationally. I suspect the names that you read and write will be in
whatever your macOS takes to be the local language. Thus
nightShiftSchedule uses English regardless of locality, whereas profile
uses local names. Thus, your program can get consistent international
behavior by using row numbers to specify profile and English names to
specify nightShiftSchedule.

% Your screen’s display profile is a video lookup table, it
affects the color and luminance of everything you display. Apple allows
programmers to read and write the current color profile, which is in
memory, and I think that there are several consumer apps that do that (in
much the same spirit as Apple’s Night Shift and TrueTone)). System
Preferences: Displays is unaware of such changes. Clicking on the profile
name that is currently in use has no effect. Clicking on any other
profile causes it to be loaded, fresh from the disk master. So, when you
ask MacDisplaySettings to activate a profile that is already current, it
plays safe and first clicks another profile and then clicks on the one
you specified, to be sure that it loads fresh from disk.

% ERROR REPORTING is strict. Out-of-range or unrecognized arguments
produce fatal errors if detected by MacDisplaySettings.m; when such
errors are detected in MacDisplaySettings.applescript they are merely
flagged by a message in the optional output argument errorMsg. When
throwing a fatal error, if Psychtoolbox is present on the MATLAB path,
then MacDisplaySettings first closes any open windows (by calling
Psychtoolbox “sca”), so the error message won’t be hidden behind your

% REQUIREMENTS: macOS and MATLAB. (If it detects Psychtoolbox, then it will
use the “sca” command to close windows before throwing a fatal error.) In
its current form, MacDisplaySettings has only been tested on macOS Mojave
(10.14) localized for USA. Earlier versions of this code supported macOS
10.9 to 10.14. It’s designed to work internationally, but that hasn’t
been tested yet. It was tested on MATLAB 2019a, and very likely works on
any version of MATLAB new enough to include structs. I think, but haven’t
checked, that the MATLAB code is pure basic MATLAB (no toolboxes) with
one negligible exception. Before throwing an error, we check for the
presence of the Psychtoolbox, if present then we call the Psychtoolbox
routine “sca” (Screen Close All) to close any open windows, so the error
won’t be hidden behind your window. MacDisplaySettings.applescript needs
only the macOS. It should work on any screen, including an external
monitor, but it’s only been tested on the main screen.

% DEVELOPERS. To write Applescript like this, I strongly recommend that you
buy the Script Debugger app from Late Night Software. and the UI Browser app from UI Browser by
PFiddlesoft. The Script Debugger is a
the best Applescript editor and debugger. The UI Browser allows you to
discover the user interface targets in System Preferences that your
script will read and set. With it you can do in an hour what would
otherwise take days of trial and error.

% APPLE SECURITY. If the user has not yet given permission for MATLAB to
control the computer (in System Preferences:Security &
Privacy:Accessibility), then we give an error alerting the user to grant
this permission. The error dialog window will say the application
(MATLAB) is “not allowed assistive access.” The application needs an
administrator’s permission to access the System Preferences. A user with
admin privileges should then click as requested to provide that
permission. This needs to be done only once for each application.

% PROFILE ROW NUMBERING. Note that when you look at the list of profiles in
System Preferences:Displays:Color there is a line separating the top and
bottom sections of the list. Apple assigns a row number to that line, but
trying to select that row has no effect and returns an error in errorMsg.

% WHAT “BRIGHTNESS” CONTROLS: Adjusting the “brightness” setting in an LCD
controls the luminance of the fluorescent light that is behind the liquid
crystal display. I believe that the “brightness” slider controls only the
luminance of the source, and does not affect the liquid crystal itsef,
which is driven by the GPU output. The luminance at the viewer’s eye is
presumably the product of the two factors: luminance of the source and
transmission of the liquid crystal, at each wavelength.

% INSTALLATION. Just put both the MacDisplaySettings.m and
MacDisplaySettings.applescript files anywhere in MATLAB’s path.

% MULTIPLE SCREENS: Seems to be working, not yet thoroughly tested. Color
Profiles work for all monitors. Our code gives equal status to all
monitors, but Apple severely limits the Display options for external
monitors, and often provides them only for Apple monitors. We provide
access to all the controls you see in the windows of System Preferences:

June 25, 2017. wrote “Brightness” for the
Psychtoolbox, and later “AutoBrightness”.
July 16,2019 Improved by looking at code here:
April 2020. Wrote MacDisplaySettings, based on Brightness, but enhanced
to also support Automatically, True Tone, Night Shift, and Profile.
April 14, 2020. Added wait loops (in the applescript) to wait for “tab
group 1” before accessing it. This has nearly eliminated the occasional
time out failures, in which MacDisplaySettings.m returns [] for
brightness and automatic, but returns correct values for night shift.
May 3, 2020. In the Applescript, I now “activate” System Preferences at
the beginning (and reactivate the former app when we exit), and this runs
much faster. Formerly, delays of 60 s were common, with occasional time
outs. Now it reliably takes 3 s.
May 7, 2020. Shortened the help text, reducing redundancy. Check for
unrecognized fields in newSettings. Improved error reporting.
May 8, 2020. Enhanced to support arbitrary screenNumber, i.e. external
May 9, 2020. Improved speed (from 3 to 1.6 s) by replacing fixed delays
in applescript with wait loops. Enhanced the built-in peek of brightness
afer poking. Now if the peek differs by more than 0.001,
MacDisplaySettings waits 100 ms and tries again, to let the value settle,
as the visual effect is a slow fade. Then it reports in errorMsg if the
new peek differs by more than 0.001. In limited testing, waiting for a
good answer works: the peek-poke difference rarely exceeds +/-5e-6 and
never exceeds 0.001. It’s my impression that if we always waited 100 ms,
then the discrepancy would always be less than +/-5e-6.

% ACKNOWLEGEMENTS. Thanks to Mario Kleiner for explaining how macOS
“brightness” works. Thanks to for sharing his
applescript code for dimmer.scpt and brighter.scpt. And to Hormet Yiltiz
for noting that we need to control Night Shift.

% SEE ALSO: % True Tone % Night Shift
Screen ConfigureDisplay? % In Psychtoolbox
ScriptDebugger app from Late Night Software.
UIBrowser app from PFiddlesoft.

Path   Retrieve current version from GitHub | View changelog