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Terrain Photography - Resizing & Storage


Digital photographs are made up of grid of dots where each dot can be set to one of a given number of colours. Below for example we have our TG icon displayed at normal size and then enlarged such that you can see each of its 'dots'.

Correct size Forced enlargement

The number of colours available depends on the type of file being used to hold the data but is usually so large that the human eye cannot detect the difference between any given shade and the next closest shade to it. The size of the image in terms of how many dots wide and how many high it is are variable and this information is stored in the data file along with the image data.

Another property of a digital photograph is the size of the file needed to store its data. Some file types store the data more efficiently than others (more about that later) but it is generally true to say that the bigger a picture is, the larger the file needed to store it.

So why should we care how big an image is?

It is important to realised that the amount of data needed to display a picture on a computer screen is much smaller than the amount needed to print one. This is because computer screens usually display images at a resolution of 72dpi (dots per inch). This means that an image which is 100 dots wide will be about 1.3 inches wide on the screen. On the other hand, even a fairly basic inkjet printer will be capable of printing an image at 300dpi which means that our 100 dot wide image only contains enough data for a 0.3 inch wide print!

Modern digital cameras are geared up to take pictures that are suitable for printing. Thus the image files that come from them are much bigger than those needed for display on the computer screen. This is an issue for two reasons:

  1. If an image is to be displayed on the Internet then all of the data in the file has to be transmitted before the viewer can see it. If the intention is simply to view it on their screen, and that is usually the case, then there is no need to send them all of the data that would be needed to print it. Indeed doing so just means that they have to wait longer for the image to be displayed.

  2. If you have no intention to print your own images and just want to display them on your own computer screen then you will be wasting space, and slowing down your speed of access, if you store them at a size that is more appropriate to printing.

Of course you will not always know if you might want to print an image at a later date and in that case you should keep the larger image. When you are planning to upload an image to the web then you should always create a new image of an appropriate size for uploading.

Should I resize it myself?

The simple answer: yes.

A fuller answer is that if you are uploading the image to your own web space then you have to do it yourself. Even if the viewers browser shrinks it down to fit it on their screen, or you use parameters in your HTML code to shrink it onto your web pages, it is still necessary for all of the data to be transmitted to the viewer before the image can be displayed.

On the other hand, if you are uploading to a gallery such as PhotoBucket or TerraGenesis' own gallery then you may be aware that they have facilities to automatically resize images that are being uploaded. It is true to say however that these resizing functions are there to protect the gallery from overly large images and that they will not necessarily make as good a job of the resizing as a dedicated piece of photo manipulation software such as PhotoShop.

Two final things to consider:

  1. If you plan to do any colour correction, cleaning up, special effects, or make any adjustments to your image then do these BEFORE you resize it.

  2. Also give some thought to the file type that you use to store your images. Many file types use data compression to fit more data into a smaller sized file. Often it is possible to choose (in the software that you are using to save the image), the relative importance of data size and image quality i.e. the software allows you to increase the amount of data compression at the expense of image quality. How much is too much will vary from image to image and is something that you will have to experiment with. Most of the recent images shown in TerraGenesis articles have been stored as .jpg files with 15% compression.

TerraGenesis would like to thank Bushdoctor for posting much of the information upon which this article was based on our forum.

Return to our index of photography articles.


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