Many people ask the question concerning which program to use: Illustrator or Photoshop? The truth is that all programs have their strengths and weaknesses. And both programs perform best within their own realm of expertise. There are basically two types of graphics programs with the main difference as to the method in which they store their digital data. Adobe Illustrator is vector-based program meaning that the data is stored as mathematical formulae, which is the best mode for storing line-based artwork or illustrative graphics.
An example of vector artwork could be an A5 image which consists of a red circle on a blue background. The program stores this information using a string of binary code representing the respective circle and page sizes. It also includes some code which tells the centre and radius of the circle, as well as some code which represents the thickness, or line weight, and red colour of the circle. This is a failry small string of data, which means that Illustrator files will usually be relatively small in size. Illustrator files are also known as resolution-independent meaning that they can be scaled up or down without losing any clarity of image. As such, vector files are best for logos, illustrations and diagrams, as well as text, especially small text. If you enlarge the text, or zoom in for closer inspection you will notice no change in resolution, no blurring of the edges.
In comparison, Photoshop images, are pixel-based and are also known as bitmap or raster imagery. In the above example of the red circle on a blue background, a pixel-based file stores this data as a “map of bits” of information. Another way of looking at this is as a grid of pixels, with each pixel having a number for colour and brightness. In this way Photoshop stores the image data as a very long string of binary numbers. And hence some Photoshop files can be very large relative to a similar image as a vector file. Which may lead you to think, why not just use vector files all the time? And this depends on the type of image itself. The larger bitmap files are a better choice for photographic imagery, which is also known as continuous-tone imagery. In such images resolution is the big issue, usually denoted as pixels per inch (ppi). Some countries may use the metric pixels per centimeter, but the majority still use pixels per inch even though they generally use metric measurements. Images for web or screen viewing are generally stored at 72 pixels per inch, whereas print media always require a higher resolution of between 150 and 300 pixels per inch. The former is fine for in-house printing, whereas the latter is generally for commercial-quality printing. With higher resolution tablet devices becoming more popular, images destined for this purpose may use the higher 150 pixels per inch.
Both Photoshop and Illustrator are created by Adobe of course and are the industry-leading software in their respective fields. So there is no definitive answer to which program is best. It all depends on context and the type of image being created. And as usual, familiarity with a range of programs is the best option for the serious digital artist.
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