Optical Print Centering

Pierre Renault in rec.photo.darkroom posted a very interesting method of optically centering a print on a mount.  The original source seems to be Black & White Photography by Rand and Litschel.  Here is my equation that determines the position mathematically, and a graphic illustration of the results.

From: Russell
Subject: Re: Automatic optical centering - WAS: Square Format Framing - 1 attachments
Newsgroups: rec.photo.darkroom
Date: 2000-12-20 23:57:23 PST

Wm = Width of mount
Hm = Height of mount
Wp = width of print
Hp = height of print

Distance between top of print and top of mount = (Wm + Wp) (Hm - Hp) / 4Wm


diagram "Pierre Renault" wrote in message
news:9010E33FAcheungmomailandnewsc@ ...
> Here's how to automatically optically center any print on any board.
> Place the print to be mounted in the upper left-hand corner of the
> board.  If you are placing a print under a matte board, then place a
> piece of paper the same size as the desired cut-out.
> Bisect the vertical strip to the right of the print and draw a light
> line with a pencil from top to bottom.  Do the same thing for the strip
> below the print.  Draw a line from where the horizontal line crosses the
> vertical line you've drawn to the right edge of the board.
> Next, place a straightedge from the point on the right-hand edge of the
> board where the horizontal line ends to the bottom left-hand corner of
> the print.  Mark the spot where the line intersects the line bisects the
> vertical strip.
> Place the lower right-hand corner of the print at this intersection.
> This works first time, every time.
> Pierre

(Archived in Google Groups.)

The optically-centered print is slightly above center.  This may be more visually pleasing, because of an illusion in which a vertically-centered print seems to “sink” a little on the mount.

The following script calculates the print position and illustrates it graphically.

The units are arbitrary.  Fractions are optional.

Include the space between the mat and print edges if appropriate.  The preferred method is to center the mat window, but you may choose to center the print itself.

Rabbet width refers to the inner edge of the frame that overlaps the edge of the mount.  In the illustration, the frame stock is 2x the width of the rabbet.

Sometimes optical centering results in the top margin being narrower than the sides.  In that case, you will probably want to use one of the other centering options.

mount – width:  
print – width:  
space inside mat:  
frame rabbet width:  


draw   rotate     area ratio =  
print position – from the top:  
from the sides:  
mat widths – top:  



How big should the mount be?  It is ultimately a matter of taste.  I myself dislike mounts that seem overly large; there is something pretentious about them.  But a good image deserves a little “personal space.”  One option is to use the golden ratio ( ~ 1.6180), which dates back to Pythagoras and is considered an aesthetic ideal.  If the ratio of the mount dimensions to the print dimensions is the golden ratio, then the ratio of the mount area to the print area is the golden ratio squared, or ~ 2.62.  The area ratio is displayed above when calculating the print and mat dimensions.  I have used the visible mount area including the space inside the mat, minus any excess space at the bottom of the mat ( = the white area in the illustration at right), as this seems to determine the overall impression.  A good range is maybe 2.3 – 2.9.

When using fractions, the rounding error may have undesirable effects such as making the vertical mat space visibly smaller than the horizontal.  If the true value is closer to the 1/32nd position between two 1/16ths, the fraction is marked with a “+” (above the fraction) or “-” (below the fraction), so 1/32 accuracy may be used.  (For example,  7/16 +  is  15/321/8 -  is  3/32.)

1/16 1/8 3/16 1/4 5/16 3/8 7/16 1/2 9/16 5/8 11/16 3/4 13/16 7/8 15/16
.0625 .125 .1875 .25 .3125 .375 .4375 .5 .5625 .625 .6875 .75 .8125 .875 .9375


Text-only version for saving
Mobile version

Run this document as a smart phone app!  Specific instructions on how to do it on Android here

Photoshop script

Some members of the Photoshop community have tried the optical centering concept, by expanding the canvas then centering the original image on a virtual mount.  See Photoshop User TV:  Episode 253 for a demonstration.  Here is a photoshop script, Optical_Centering.jsx, that should do the job.  It should be self-explanatory.  If you enter a rabbet width, the hidden edge of the mount is colored black.  If you enter a mat space, the mat is colored gray so you can see the space.  You can recolor or uncolor it as needed.

Tested in CS2 and CS5.  You may need to flatten the image first.  Settings are saved to an .ini file in your default user folder.  Updated 2/1/2011.

Just to point out, if you are wanting to print an image optically-centered on a mount-sized piece of paper, you might try calculating the print position, then using it as the top margin in the print dialog.

© 2012 by Russell Cottrell.  Updated 7/9/2012.

Optical print centering tested with Firefox 3.6 - 12, Internet Explorer 6 - 8, Safari (for Windows) 4.0, Opera 9.64, Dolphin Browser HD 6.0.0, Dolphin Mini 2.11, xScope Browser - Web & File 6.43.1, Miren Browser 1.2, and Boat Browser Mini 2.4.