Resolution Explained


The revolution in resolution is here. In this technical document we explain the scientific background and the considerations leading us to design Arthur to handle the image resolutions of the future. We believe that Arthur is a strategic investment that will help you differentiate your exhibition space using tomorrow’s technology trends, today. 

Why 300 ppi scanning is not sufficient for fine art. 

300-points-per-inch (ppi) scanning resolution might be perfectly acceptable for some scanned materials, such as newspapers and printed books, but it is inadequate for e.g. manuscripts. 

Scanning resolution depends heavily on what these images will be displayed on. With the advent of higher resolution displays that are becoming available in consumer electronics like tablets and smart phones 300 ppi is no longer the safe option it once was. 
Why this is will be explained through the following 5 key points. This will also cover the unique Arthur displays and why they are an essential part of the solution for exhibitions and galleries.
  1. What resolution can the human eye perceive?
  2. Angle of View
  3. Viewing distance
  4. Why 300 ppi is not enough
  5. Issues with modern displays of personal devices

1. What resolution can the human eye perceive?

On average the resolution a healthy human eye can perceive is between 0,4 and 1 arcminute*. Before we translate this into pixels used by displays in use today, we need to acknowledge that the size of the pixel will vary with distance.

An average adult can focus at no closer than 4" (10 cm) distance from a display. At this distance the smallest pixel/dot size the eye can distinguish is 0,0116 mm or 11,6 microns (for 0,4 arcminute). For 1 arcminute, it rounds up to about 29 microns.

An inch is 25,4mm, and in that inch you can fit 2190 ppi (dpi) at 0,4 arcminutes, and 876 ppi (dpi) at 1 arcminute.
This means that if a healthy adult brings any display or printed paper to 4" (10cm) from his face, the maximum resolution he/she can see is 2190 ppi/dpi. However, the legally accepted norm of vision is 1 arcminute, which translates to 876 ppi/dpi at 4" (10cm).

arcminute is a unit of angular measurement equal to 1/60 of one degree (or π/10.800 radians). Average resolution means that human eye can see more detail only within an extremely small focused point. As distance from this point grows, the resolution that can be perceived drops.

In our calculations we strike a balance for both the comfortable viewing area (the macula area) at 1 arcminute and the extremely detailed area used for discovery (foveal cone) at 0.4 arcminutes. 

2. Angle of View

Human eye can cover 155° of horizontal angle of view, and 135° of vertical angle of view, forming an ellipse-shaped visible area. As everyone knows, only a small part in the center of our visual field is sharp and detailed, and this is what we use for reading and viewing. This is called the Macula, and it is specialized for high acuity vision. This area represents a small percentage of our visual field, and translates to roughly 40° of vision angle that is important for calculating the comfortable viewing distance. For fine details, we use only about 2° which we experience as pin-sharp (Foveola area).


3. Viewing Distance

Magazines and fine art prints are viewed from an average distance of 1 foot (30cm). At 1 arcminute, it is 89 microns or about 300 dpi/ppi. This is why magazines are printed at 300 dpi. It is good enough for most people. Fine art printers aim for 720 dpi (satisfying the more sensitive eyes at 0,4 arcminutes), and that is adequate as very few people bring their head closer than 1 foot (30cm) from a painting or a photograph.

When we are talking about digital displays, especially larger ones, the viewing distance dramatically increases. In order to fit a 60" (diagonal) display into our comfortable viewing area, we need to fit this entire display area in our vision ellipse, which will additionally increase the viewing distance.

The regular television with Full HD resolution (1920 x 1080 pixels) at 60" diagonal size needs to be viewed from a distance of 72" (183 cm) in order to completely fit it in the viewing area. 





At a resolution of 1 arcminute, a human eye can distinguish 44 ppi at a distance of 72" (183 cm). However, individuals with the best sense of vision can distinguish up to 110 ppi from the same distance.

If we now take a look at Full HD display which has a resolution of 1920x1080 pixels at 60" diagonal, it will translate to 38 ppi. This falls short of the required comfortable resolution range of 44-110 ppi.

Arthur optionally uses state-of-the-art display technology, which quadruples the number of pixels on approximately same surface, complying with 4K UHD resolution (3840 x 2160 pixels). This means that the visitors would enjoy a 60" display from a distance of 72" (183 cm) at a resolution of 76 ppi. This will be experienced as a huge improvement, presenting to the eye much more detail and producing a spectacularly rich viewing experience.

In real-life installations, this means that with an Arthur display, you can bring the viewers to half the distance that you would when using regular Full HD displays. By doing this, the viewer's field of vision will fill with a bigger display, producing an immensely striking experience. Arthur displays come in two additional, bigger sizes that will help you produce even more captivating experience for larger groups or bigger spaces.

4. Why 300 ppi is Not Enough

For the sake of simplicity and staying on topic, let's discuss the technical requirements in the area of fine arts.

As we have seen in previous points, an average eye can perceive resolution between 0,4 and 1 arcminutes where 300 ppi only satisfies the lower end of eye resolution at 1 arcminute at default viewing distance of 30cm. This is why advanced art prints are made at a resolution of 720 ppi/dpi!

When a researcher wants to take a closer look at the details of a painting or the fine illumination of a manuscript, he will use a loupe (magnifying glass), which typically offers a 3-4x magnification. It enlarges the original, revealing detail previously not visible with the limited 0,4-1 arcminutes resolution. With an enlargement loupe, the resolution experienced has at least tripled, which means that for fine art you need to scan at minimum of 900 ppi in order to be able to substitute original object's details with an electronic version. Anything less would mean that you are only enlarging pixels, but not disclosing any additional details to researcher!

Arthur is an indispensable tool for the connoisseur of fine art as it allows extremely detailed and large digital images to be viewed as a substitute to original. In this way Arthur can be used for scholarly work on material that most likely would not be allowed for personal inspections.

*Note that all resolutions in this article are discussed as true optical resolutions. Many scanners, cameras and sensors capture with some kind of interpolation and Bayes matrix sensors. This means that they artificially produce some pixels based on neighbouring pixel informations. This gives you false sense of quality!  True quality of a scan can be reached only with specialized, professional chips, sensors, lenses and filters.

5. Issues with modern displays of personal devices

Another important issue with scanning at only 300 ppi is becoming apparent on modern displays of personal devices like iPad, iPhone, Retina displays or with Android devices which reach up to 300 ppi or higher resolution. The reason for this is that manufacturers try to reach the natural maximum resolution an eye can see in order to present the viewer with the best possible quality and the natural look that the human eye is accustomed to.

If you scan at only 300 ppi and display on 326 ppi (which is what the iPhone has), the displayed image will simply be represented at a smaller scale than 1:1. Any enlargement to bring it to its natural size will result in degraded quality for the viewer who is used to their high resolution display.

Tablets and Smart Phones are intended to be held from quite close up to the eye all the way up to reading distance, typically between 7-15" (15-30cm) distance. Simply put, scanning with 300 ppi is not living up to today's standards (not to mention the likely developments in years to come)! If you would like to present the public with content that will be displayed nicely on their devices, you have to scan at higher resolutions.

Contact us, and we can discuss your precise requirements and ensure that your digitization is future-proof.