Computer Articles - Internet and Computer News » Memory Card http://www.computerarticles.co.uk This is an archive of the work of Chris Holgate, first published in the weekly Herald Express Click column. Tue, 19 Jul 2011 10:32:30 +0000 en hourly 1 http://wordpress.org/?v= Image Resolution FAQ http://www.computerarticles.co.uk/image-resolution-faq/ http://www.computerarticles.co.uk/image-resolution-faq/#comments Fri, 24 Jul 2009 16:33:35 +0000 admin http://www.computerarticles.co.uk/?p=1445 A question I’m currently receiving on a weekly basis is ‘how many pictures will I be able to fit on this’ when a customer is referring to the size of memory card or USB Flash Drive.  Understanding image resolution and size is important in this digital age and although the intricacies are incredibly complex, the [...]]]> A question I’m currently receiving on a weekly basis is ‘how many pictures will I be able to fit on this’ when a customer is referring to the size of memory card or USB Flash Drive.  Understanding image resolution and size is important in this digital age and although the intricacies are incredibly complex, the basics are pretty easy to get to grip with.
What is Image Resolution?
A pixel is a unit of programmable colour on a computers display and by combining many of them together we are able to create an image; the term resolution typically refers to the number of pixels that are used in this process.  On the whole, the quality of the image will increase with a greater number of pixels as we are able to store a greater amount of detail.

How is Resolution Measured?
Resolutions are generally expressed in two different formats – either the pixel dimensions of the image are given or the total number of pixels used in its creation.

Most digital cameras express their maximum resolution in terms of megapixels (millions of pixels) that can be used to create an image; an 8 mega pixel camera would be able to break a picture down in to 8 million pixels hence giving a higher resolution that a 5 mega pixel camera.

The resolution of a computer image on the other hand is usually expressed by giving the number of pixels present on a line and the number of lines used in the image.  For example, an image measuring 1600 x 1200 would contain 1600 pixels per line and a total of 1200 lines giving a total of 1,920,000 pixels (1.92 mega pixels).  As the image contains a greater number of horizontal than vertical pixels we can assume this picture would be landscape rather than portrait.

How does Resolution affect File Size?
The more pixels an image contains the larger the file is likely to be; this is due to the fact that storing information relating to 10 million pixels is liable to require more space than saving a lower resolution 1 million pixel image.

There are several other very important factors to consider:

File Format – Over the years there have been many different image file formats, each introducing new advantages and disadvantages and covering them all would take an article in itself.  The two you are most likely to come in to contact with when using a digital camera are JPEG (smaller images that often include compression) or RAW (Completely unprocessed images files which are of a higher image quality but also substantially larger)

Colour Depth – Along with the total number of pixels that constitute an image, we also have to consider the potential number of colours each pixel could be.  If, for example you save your image as a ‘line art’ image where each pixel can be either black or white then the amount of data required to store this information is less than if you set a colour depth of ‘true colour’ where each pixel could be one of 16,777,216 potential colours.

Compression – Many image formats, such as JPEG allow you to adjust the amount of compression that is utilised when saving the image.  Compression can work in a number of different ways but ultimately it works to minimise the amount of data required to save the image.  This is usually achieved by looking for areas of commonality (for example a shape or pattern) and saving the description of that area which the computer can then later reproduce when reloading the image rather than defining each individual pixel.

]]> http://www.computerarticles.co.uk/image-resolution-faq/feed/ 0 Readers suggestions http://www.computerarticles.co.uk/readers-suggestions-2/ http://www.computerarticles.co.uk/readers-suggestions-2/#comments Fri, 26 Aug 2005 13:55:27 +0000 admin http://www.computerarticles.co.uk/?p=43 Once again I’ll take the time off this week to help one of my readers take care of their computer woes.

I wonder if you could help, I am looking for some free software which “undeletes” pictures from an SD media card. I accidentally (believe it or [...]]]> Once again I’ll take the time off this week to help one of my readers take care of their computer woes.

I wonder if you could help, I am looking for some free software which “undeletes” pictures from an SD media card. I accidentally (believe it or not) deleted my holiday pictures by cutting the file from the camera card and then thinking I had copied them I deleted them off my PC!

Paul Wright, via e-mail

I should start this article by briefly explaining exactly what we mean when we use the term undelete. Many people think that what happens when they delete a file from their computer is that it is physically removed from the hard disk or media device you are using never to be seen again. What actually happens is that the Operating System simply marks the area of space that was once used by that file as being available to use and hides the file from the view of the user – it doesn’t physically disappear from the disc until the computer decides to write data to that area. This explains why in legal cases involving data being used as evidence the computer of the accused is given to forensics to analyse so that they can try and recover data from the hard drive that may been purposefully deleted.

A SD (Secure Digital) card is a memory card that is primarily used in digital cameras for storing pictures. I had always assumed that as a static memory device that a SD card would be a different kettle of fish and that once a file had been removed from the card that it would be lost forever however on closer investigation it would appear that they work on the same principle when it comes to recovering lost files.

After spending half an hour searching the Internet for an appropriate program I discovered the PC Inspector site (www.pcinspector.de/file_recovery/uk/welcome.htm) which would appear to do the job you require perfectly. To test the application I filled an SD card up with pictures then deleted them and PC Inspector then managed to recover them all. Additionally the site includes a version of this program to recover files that you may have lost on a floppy or hard disk and best of all these utilities are completely free of charge. It is worth bearing in mind that if since deletion the space that your files once occupied has since become filled that these undelete programs will be essentially useless.

The site also includes several other helpful pieces of software such as a utility to permanently delete files that you don’t want to ever be recovered, a hard drive cloning utility and several other useful programs that are free if charge.

An undelete program is something that most people should have on their computer as it is certainly something that you’ll use once in your lifetime; I know I have. Whether you require to recover a file from floppy disc, static memory card or your computers hard drive there is a utility out there that can help you. If you try PC Inspector and don’t find it to your liking then do check out http://www.snapfiles.com/freeware/system/fwdatarecovery.html where you will find a dozen or alternative free utilities.

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