WEB POSTER EXHIBITION - Impossible to show

More and more often I am getting posters that are impossible to show on Poster Page, see for example Philippe Apeloig 1, Philippe Apeloig 2, Leonardo Sonnoli, Mehdi Saeedi, Bi Xuefeng. Below are screen shots of another example, a poster made by Ole Haentzschel, a student of Melk Imboden at the University of the Arts (UdK) in Berlin, seen in different magnification on my monitor:

To show that these are quite different pictures, and not just smaller versions of the same poster, I have scaled two of them back to the same size for easier comparison. The lower part of the poster in particular changes in unpredictable ways.
In the digital photo of the poster, the mushy black and white background is not due to bad printing or bad weather, the lines are perfectly clear and evenly spaced in the original.

The reason for all this chaos is explained by Shannon's sampling theorem, a basic law of information theory. Roughly translated into plain english, it says that you can not paint a life size picture of a mouse with an elephant size brush, and conversly that you do not need a mouse size brush to paint a life size picture of an elephant.

Applied to Ole's poster as seen on Rene's monitor, it is a matter of hit and miss whether his lines just fall on a pixel of my display or not. Let's look at the numbers: My monitor is about 36 cm wide and has a horizontal resolution of 1024 pixels (as most of the readers of Poster Page have, see the table below, taken from my visitor statistics program):

Screen ResolutionsUnique Visitors
  1024x768    180313    50.51%  
  800x600    57544    16.12%  
  1280x1024    57021    15.97%  
  1152x864    37128    10.40%  
  1600x1200    11668    3.26%  
  Other    11046    3.09%  
  640x480    2232    0.62%  

One pixel on our monitors therefore has a size of (36 cm / 1024) = 350 microns (= 0.35 mm). If a poster of 100 cm height is shown as a 10 cm picture, this means that a line with a diameter of 3.5 mm on the poster is just one pixel wide on the screen, not enough according to Shannon's theorem, which says you need at least twice the resolution to show it properly. No amount of sharpening software or contrast enhancement will get you around this theoretical limit. Objects smaller than about 7 mm are just impossible to show on Poster Page, and on my monitor. If you are more familiar with other units of measurement : Current monitors have a resolution of about (25.4 mm / 350 microns) = 72 dpi (dots per inch), or a meager 1 Megapixel.

Better monitors ?
Computer technology is a wonderful field, so we soon may have much better monitors. What are the theoretical limits here? It is of no use if your monitor has a super high resolution when your eyes are not sharp enough to see it. I looked up Wikipedia to find the size of the pixels, or cone cells, in the human eye, it is given as between 1 and 4 microns (0.001 to 0.004 mm), depending on wether they are in the center of the eye or rather at the periphery of vision. Their total number is given as about 6 million, so the human eye has the same resolution as a standard digital camera of 6 Megapixels.

The cone limited resolution of the eye when projected on the computer screen is between 30 and 120 microns, assuming a reading distance of 60 cm and an eye focal length of 2 cm ( = 1 micron * 60 cm / 2 cm ). The development of higher resolution computer screens has almost reached its end, and only has to improve by a factor of 3, or maybe 10, to reach the limit given by the anatomy of the human eye. Maybe the monitors will grow in size, up to 2 by 3 meters, but not on my desk. Making better monitors is therefore not much of a solution to our problem.

Sharper lenses ?
In practice, the sharpness of vision is not so much limited by the number of cone cells in the eye, but rather the imperfections of the lens, and also the inability to focus properly once you are over 50 years old. The maximum possible sharpness of a lens, the diffraction limit, depends on the wavelength of visible light and the aperture of the lens, in our case the diameter of the pupil. Assuming 0.5 microns for the wavelength and 5 mm for the pupil, we arrive at a resolution of about 60 microns at a reading distance of 60 cm. Quite remarkably, it is almost identical to the resolution stemming from the limited number of cone cells. Nature has apparently decided that it does not make sense to grow a lot of receptors if the eye can not use them because of optical reasons.

Consequences for poster design
I realize, with some resignation, that not all posters are designed with the sole intention to look good on the screens of the Poster Page, some are also designed to be seen outdoors. If you redo the above calculations assuming a viewing distance of 10 meters, you arrive at the conclusion that no important detail on the poster shood be smaller than 1 mm if you expect it to be noticed from across the street. For a good picture on Poster Page, make it even bigger. Armin Hofmann, Kari Piippo, Lech Majewski, even Toulouse-Lautrec knew this quite well:

home  previous exhibitions  page created on August 22, 2005 / this section is part of Rene Wanner's Poster Page /