I had a situation come up with a client not too long ago where the client wanted a JPG file for their website in a specific size. When they increased the size they were surprised to find it pixelated because the PDF of this same image didn’t do that. I wrote them a nice email explaining why this happens, but then I started to think that perhaps many other people don’t understand why this happens. So here are some common questions and answers to explain this to you!
Q: Why do some files get blurry and others don’t always do that?
A: They are different types of formats. The two format types are known as Raster and Vector. Raster graphics will always pixelate when enlarged while Vector graphics won’t.
What is a Raster Graphic?
A: A Raster Graphic (also called a Bitmap) is made up of little squares known as pixels. The word Pixels is actually a contraction for “Picture Elements” with the word picture shortened to “pix”. The more little squares you can fit in a given space the higher the resolution. These types of files look best at the size they were created in or at size smaller than their original dimensions. They will break apart and appear blurry (pixelated) when they are magnified or increased to a larger size. Certain programs, such as many of the popular photo editing software programs, will always only work in Pixels.
Q: What is a Vector Graphic?
A: A Vector file uses a series of mathematical curves that go through points or nodes with in the file to create the image we see. This is what allows the image to resize cleanly with out pixilation. Vector files are often referred to as ‘scalable’ because of this feature. What all this means is that the dimensions of the file aren’t locked into the size it was created in in order to look it’s best. It can be made into any size from much smaller than its original size or much larger than its original size at it will look very crisp and clean with no blurred edges at any size. Certain programs, such as many popular computer drawing and drafting programs, use vectors as their main format of image creation.
Q: Can you save from a Vector Graphic to A Raster Graphic?
A: You can save a vector graphic to a raster graphic. When a vector is saved to a raster graphic the file is transformed from mathematical lines and curves to pixels. This process is sometimes known as “rasterization” or “rasterizing”. During this processes all the information about the mathematical lines and curves that originally made up the image is lost and all that remains is the information regarding the pixels. Unfortunately, you can’t “un-rasterize” a file.
Here is an example from outside the Graphic Design world to illustrate this: A caterpillar (vector graphic) goes into a cocoon and emerges as a butterfly (raster graphic). The caterpillar is gone now. The butterfly can’t go back into the cocoon and come back out as caterpillar. It’s a one-way process. The same goes with converting Vector graphics and Raster graphics.
Q: What about from a Raster Graphic to a Vector Graphic? Can you do that?
A: Unfortunately, No. A Raster Graphic can’t be saved as Vector Graphic. In order to change a raster graphic to a vector graphic the image would have to be redrawn in vector based drawing program such as Adobe Illustrator or Corel Draw to name a few and then saved in a compatible file format.
Q: How do I know if my file is a Raster File or a Vector file?
A: Some common file types such as JPG, GIF and PNG files are always Raster files. Common file types that are always vector include AI, EPS, SVG, and CDR. Other common file types such as PDFs can be either a Raster or a Vector. If you ever aren’t sure what file type you’re dealing with here’s an easy test one of my clients taught me: Put the file into the photo viewer on your computer and then magnify the image from 100% to 200% if it suddenly goes from sharp and clear to blurry it’s a raster, but if it still looks crisp it’s a vector.
Now you know why some files pixelate and others don’t!
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