Byte Me Article 231 – Resolution more than meets the eye

Resolution More than Meets the Eye

Following on from last weeks’ article about computer screen connections, this week we look at screen resolution and refresh rates and their effect on the overall computer experience.  This is a particularly ‘hot’ topic as it also relates to the current crop of new ultra-high definition TV’s as much as computer screens.

To fairly examine this topic we need to understand that not only does the resolution of a screen matter but also the size of a screen & the resulting dots per inch (dpi) – and also how far we are sitting from the screen and the type of content that we are viewing.

The resolution of a screen or even a digital photo for that matter is the number of lines (horizontal & vertical) it is divided into.  A popular example is the label ‘1080p’ which has 1080 horizontal lines and 1920 vertical lines.  At every intersection of this cross hatch of lines we have a pixel – which in layman’s terms is a coloured dot.  So thousands or even millions of these different coloured dots make up an image.

2015-07-25 Byte Me Artilce 231 - Screen Resolution

Next we need to consider screen size because if we had a smart phone with a 1080p resolution then the pixels are way finer than a 42 inch 1080p colour TV.  What manufacturers are trying to achieve is to have the pixels fine enough that we cannot discern the individual dots with the naked eye – at a normal viewing distance.  As a result it is unfair & of little comparative use to walk into a TV retail store to put your nose to a TV screen and declare that it has too low of a resolution because you can see the individual pixels !

There are charts and approximate guides as to how far apart the pixels need to be for varying viewing distances so that the individual pixels effectively ‘blend’ into one another to constitute a more true-to-life image to the average human eye.  To give you an approximate idea please consider the following.

If we hold something about a foot away (like a smart phone) then we can likely detect individual pixels down to as fine as around 300 dpi – with average eyesight.  If we are around 2 feet away (like sitting at a computer screen) then we are may be able to distinguish less than half of this pixel intensity – around 125 dpi.  Moving back to around 10 feet which is a typical TV viewing distance then we are unlikely to detect individual pixels as sparse as even 25 dpi.

If we correlate this to achieve a ‘real life’ image on varying screen sizes using a constant 1080p resolution then the smart phone screen should be no bigger than about a 6” diagonal, the computer screen around 18”, however the TV screen could be as large as an 80 inch!  Keep in mind that if you walked right up to an 80” 1080p TV it would look horrible and grainy to the naked eye.  So if you plan on being closer than the above distances then either a smaller screen or a higher resolution screen would be provide a more true-to-life viewing experience.

The other influence is image content.  If we are viewing a movie then we are less conscious of all of the above than if we are typing a document.  This is one reason why TV’s normally work well when hooked to your computer – until you try editing a spreadsheet or document.  Right now I am using a 40” TV screen at a distance of about 3 feet and it is perfect for fine text – however it is an ultra-high definition model with a resolution of 4095×2160 (four times as many pixels as a 1080p model).  Coincidentally this size/resolution works out to about 100dpi.

Apart from all of the above science another important consideration when chasing a ‘nice’ true-to-life image on our screens is that of refresh rates however this topic will be explored next week. 

Future Byte Me topics can be emailed to [email protected] and Bruce is contactable at Kerr Solutions, 205 Musgrave Street or on 49 222 400.

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