### How good originals is needed

A common issue is the resolution of an image must have. Unfortunately there is no easy answer to this, it depends on…

- How good the original is, it is definitely not just about resolution and megapixels!
- What kind of design it is.
- How much printing will be.
- Viewing distance. A big picture look is normally not as close to.
- Type of paper or canvas. A structure often cheat the eye and is more forgiving.
- How good sight you have.
- What it is for betraktningsbelysning. Here are cheating often!

Some rules of thumb, you can still calculate. Since it is true but not exactly since it is not possible to compare the printer's resolution in DPI and camera in PPI. We take three examples, A4, A3 and A2. Normally, you write out the 300 DPI (dots per inch). Epson writes in and out with 360 DPI (native resolution). An A4 would then have 8,4 Megapixels, A3 16,7 megapixlaroch A2 33,4 Megapixels. Now press your nose against well not picture any more than sitting two dm from its 42 inch TV. The following viewing distances are perhaps more realistic.

- A4 – 55 cm, when sufficient 4 Megapixels
- A3 – 77 cm, when sufficient 5 Megapixels
- A2 – 110 cm, when sufficient 6 Megapixels

There is a simple rule to calculate an approximate viewing distance. One takes 1,5 x diagonal. For an A2 image would thus be 1,5 √ x 42 ² + 60² ≈ 110 cm (pythagoras kit).

### This is obviously not an exact science, it depends, as I said at…

What if the pixels are not enough? Well then we can interpolate, ie mathematically add pixels. Is it not too large differences, it works well with PhotoShop. Special programs like Perfect Resize (formerly Genuine Fractals) claim they can do to increase the size 1000% without loss of sharpness or detail. I use both Perfect Resize and a”fattigmansRIP” called QImage Ultimate. QImage have the opportunity to choose 12 different interpolation methods. They have their own method called fusion with Deep Focus Sharpening (DFS). It gives a very good result which suppresses so-called artifacts or “glowing edges” although the picture tightened too much when printing.

Another interesting question is how high-resolution (DPI) as the eye can see the difference between. A picture in this case is digital if we assume that it consists of a variety of small ink dots. The eye is analogous and what we see is more considered as a stream of reflected light. The only sensible way is to test and of course it differs from person to person. Normally we say that the limit is 250 – 300 DPI. A modern, good printer high quality suffices.