Bitmap VS Vector
Programs use different formats to produce a desired effect and they all work differently. We primarily use Illustrator, Photoshop and InDesign. To give our clients the best possible final product we may use art from all three programs to create their final document(s).
Understanding of the differences between the two major 2D graphic types: bitmap and vector images is an important lesson and often a tough one to grasp. If you work with graphics at all, it’s bound to come up, so it’s an important concept to understand. Below is an explanation of each program and the concerns encountered in enlarging or reducing the different art elements. Bitmap or Pixel • Bitmap images (aka- Raster images) are made up of pixels. • Pixels are tiny squares of individual color that when combined together make up an image. • All scanned images and images from digital cameras are bitmaps. • Bitmap images are resolution dependent. Resolution refers to the number of pixels in an image and is usually stated as dpi (dots per inch) or ppi (pixels per inch). • Higher resolutions mean that more pixels are used to create the image, resulting in a crisper, cleaner image. • Bitmap images are displayed on your computer screen at screen resolution: approximately 100 ppi. But a bitmap image for printing needs 300 ppi. • Increasing a bitmap image will sacrifice quality. • Reducing the size of a bitmap image through a software’s resample or resize command, throws away pixels. • Increasing the size of a bitmap image through a software causes your software to create new pixels, but it can only make guesses as to what is accurate — it can’t create any more detail than what was there originally. • Zooming in and out, or dragging the edges of your images in a page layout program to resize it is called scaling. • Scaling an image does not change the number of pixels in the image. • if you scale a bitmap image to a larger size in your page layout software, you are going to see a definite jagged appearance. By scaling your photo larger you are basically spreading out the pixels. Even if you don’t see it on your screen, it will be very apparent in the printed image. (See example below.) • When you scale a photo smaller you create higher resolution by squishing the pixels closer together, creating more detail. EXAMPLE: Imagine you have a tiny box of raisins. This raisin box represents a photo pulled from a web page. Your box has 72 raisins in it. These raisins represent the number of pixels per inch in your photo from the web. Now imagine you pour your 72 raisins into an empty family size box of raisins. This represents what happens when a photo for the web is scaled to fit a photo in a printed brochure. The raisins will expand to fill the large space. So the photo becomes extremely jagged because the pixels have enlarged to fill the space but the same amount of photo information is there it has not increased. Common bitmap formats include: • GIF • JPEG, JPG • PNG • PICT (Macintosh) • TIFF • PSD (Adobe Photoshop) Key Points About Bitmap Images: • pixels tiny dots in a grid • resolution dependent • enlarging reduces quality Vector • Vector images are made up of many individual, scalable objects defined by mathematical equations rather than pixels. They always render at the highest quality. • Scalable objects may consist of lines, curves, and shapes with editable attributes such as color, fill, and outline. • Vector images are resolution independent. You can increase and decrease the size of vector images to any degree and your lines will remain crisp and sharp, both on screen and in print. • Fonts are a type of vector object. • Vector objects can be any shape • Vector images are transparent where there is no object. • Vector images are usually made up of solid areas of color or gradients, but the continuous subtle tones like a photograph are difficult to achieve. • Vector images originate from software. You can’t scan an image and save it as a vector file.Vector images can, quite easily, be converted to bitmaps. This process is called rasterizing. • The most common reason for wanting to convert a vector to a bitmap would be for use on the Web. • When you convert a vector image to a bitmap, you can specify the output resolution of the final bitmap for whatever size you need. • Once converted to a bitmap, the image loses all the editing qualities it had in its vector state. • If a different size is needed, go back to the original vector file and export the image again. Common vector formats include: • AI (Adobe Illustrator) • EPS What About Metafiles? Metafiles are graphics that contain both raster and vector data. For example, a vector image that contains an object which has a bitmap pattern applied as a fill, would be a metafile. The object is still a vector, but the fill attribute consists of bitmap data. Key Points About Vector Images • scalable • resolution independent • no background • inappropriate for photo-realistic images • metafiles contain both raster and vector data InDesign is a desk top publishing program. Once the text is ready, the photos are chosen and the drawn images are prepared they all come together in an InDesign file. When we create an ad or brochure we create it to the actual size it will be printed. We make sure that the ppi of the photos are large enough and the colors are either in printing process colors or in spot colors. We also format the text to fit correctly. |