Digital Photography 101

Chapter 6: Image Editing Software

6.1: File, Formats and Resolutions

There are a number of file formats that are useful to photographers depending on intention of use. All of these files can be opened and manipulated in Photoshop. Firstly let's look at the program's daughter file or the Photoshop file, identified with this extension after the dot (.PSD)

PSD is a Photoshop file and holds image and data information important to all the features of Photoshop. Saving in this file format will hold layers and selections intact so they can be worked on separately. If you intend making future changes to your files then this is a very useful file format. Most print labs can also print from a PSD file. The memory size measured in megabytes is large (5 -50 Megabytes for high resolution) so Photoshop files are not easily transferred over the internet via email or posted on websites. Some other graphic applications will run and manipulate Photoshop files but you are best to use the mother program of Photoshop.

JPEG (Joint Photographic Experts Group) files are very universal and have fast become industry standard for print ready files in most labs, mainly because of the low memory size meaning they are easily moved around the world. They are also standard for images posted on websites. JPEG files are compressed and therefore small in file size. (2 -5 megabytes for high resolution at high quality). JPEG files should only be resaved a few times as images data is disregarded each time depending on the compression levels selected. We will look at this in more detail when we cover optimisation later in this chapter.

TIFF files are short for Tagged Image File Format. Similar to JPEG files these files can be compressed to create a more manageable file size. About twice the memory of an identical JPEG file. The big advantage of TIFF is that all image data can be retained each time the file is resaved. This file is also industry standard in print labs and graphic design companies. If your photos are going to be further processed or added to documents in a design house then the files are better to be sent as TIFF files and burnt to CD if your Internet speed is slower.

So what is the best file to use for prints? Frankly there is little or no difference the human eye can see on good RGB printers. If all file formats are of high quality then you won't see any difference unless your eye is super trained. Yes that's right! A fifty-megabyte PSD file can print the same as an identical JPEG file, which is only three megabytes. The most important thing to consider is shooting well-exposed original photos at a high resolution.

Resolution can be confusing. It is best described as the number of pixels in an image. A pixel is a tiny square, which the computer assigns a 6-digit code, which corresponds to a colour. They make up your digital photo like pieces of a jigsaw puzzle. It the pixels are numerous enough then the human eye will blend them with gradual mixing of colour and tone. You may have heard of DPI? Well this stands for Dots per Square Inch or pixels per square inch PPI . Most printing labs will print your photos at 200 to 400 DPI and it pays to know what they do. At these resolutions the pixels will become blended to the human eye at hand distance on quality paper. The massive billboards you see are printed at very low DPI because they are viewed at a distance. Come in close to the billboard and you will easily see the dots or individual pixels. Four Colour Printing or CMYK needs a much higher resolution (300 DPI) and a better quality file then the typical Lazer and Ink jet RGB printing methods in smaller print shops. Again we will look at these printing methods later in this chapter. It is important for you to have a good understanding of how your photos are going to be printed. If you are a professional then visit a large print house if you can and talk to the managers about printing digital files. Your screen resolution is also measured in pixels, but because light is coming out of the screen rather then being absorbed and reflected by a print the resolution can be much smaller. 72 DPI is standard for your typical monitor resolution.

We can now see that resolution can be used to express the total number of pixels in our file such as six million (3000 x 2000) pixels or it can be used to express the total number of pixels in each square inch of our photos (DPI and PPI).

Resolution has a direct bearing on the size of your print and the data memory consumed by the file. The measure you should become accustomed to is the pixel length of the longest side of your file. From here you will soon get an instinctive idea of what is required from your photo files. For example:

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