Pixels, screens & printing Resolution Pixels, screens & printing

What is a pixel? The smallest element in a picture – a picture element or pixel. A megapixel is the collective term for 1,000,000 pixels. The Nikon 5100 produces an image file comprising 16.2 megapixels.

Pixels on a screen... Most modern monitors have a ‘native resolution’ of around 72 pixels per inch (ppi). Therefore an image shown 1:1 on a monitor which is 720 pixels wide would measure 10 inches across the screen.

Pixels on paper... Most modern printers print at around 300 ppi. You may know about dpi – for the purposes of today see ppi as dpi. Therefore our picture of 720 pixels in width would, if printed 1:1, measure around 2½ inches wide on paper.

Not Enough Pixels If you wanted to print a low-resolution picture (720 pixels wide is low resolution) and wanted to print it above the size of 2½ inches you would risk having your picture start to pixellate (the square pixels showing in your print and distorting the image). A possible solution is...

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...Interpolation This is a solution offered by software and involves the computer inserting extra pixels in your picture according to the neighbouring pixels and thus increasing the size of the image.

The Nikon 5100 16.2 million pixels gives us an images which is 4,928 x 3,264 pixels. This creates a compressed file size of around 6Mb. NOTE:- this is the highest resolution. This is based on a high quality JPG file (8-bits per pixel). A RAW file is larger (14-bits per pixel).

Printing from a Nikon 5100 4,928 x 3,264 pixels = a printed size of around 15”x11”. Realistically you should be OK in printed up to 20”x15”. RAW files...

A RAW file This is the unprocessed data as it comes out of the light sensor in the camera – truly raw data. When a picture is converted to JPG it loses some of the data content. A raw file is uncompressed and usually has a JPG embedded in it – these factors combine to create a much larger image.

Advantages of RAW Exposure latitude – if you have a raw file which is noticeably over- or under-exposed you have a much greater chance of recovering or discovering usable content in the file. If you have colour casting a raw file is a better bet for recovering the image.

Processing RAW Files Photoshop products include a raw file editor (Adobe Camera Raw). This software is regularly updated for different cameras. NOTE:- every camera deals with and produces slightly different raw files and you need to make sure your software is up-to-date and ‘knows’ your camera.

Exposure adjustments stepped in f-stops. The histogram – spread of tones and colour across the image. You cannot makes changes to this at this stage. A key part of a RAW file is the white balance. Here you can alter the picture white reference point (see below). Exposure adjustments stepped in f-stops. A set of ‘filters’ to adjust and remove colour casts from different light sources.

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