Chap9 10
- 1. Describe the various graphic formats used in digital media.
- 2. In This Chapter, you’ll learn on: The Basics of Digital Image Formation Identifying of the Various file types such as JPEG, GIF, AI, PDF and etc The Characteristics and use of the Various Graphic Formats
- 3. In this chapter, we will look at the basic types of digital images and file formats. Images, such as pictures, clip art, 3-D graphics, and animation, are commonly used in designing for both multimedia and the Web. Regardless of their forms, multimedia images are generated by the computers in two ways: as vector- based graphics and bitmap images
- 4. The Basics of Digital Image Formation Vector graphics Vector-based images are defined by mathematical relationships between points and the paths connecting them to describe an image. Graphical elements in a vector file are called objects. Each object is an independent entity with properties, such as color, shape, size, outline, and position on the screen, by its definition. Since each object is a self- contained entity, you can easily move and change its properties while maintaining its original clarity, and without affecting other objects in the illustration.
- 5. Object graphics are very little memory because only the location and design information must be defined – very simple values. This also applies to the colors used in object graphics, which are also expressed numerically. These characteristics make vector-based programs ideal for illustration and 3D modeling, where the individual objects usually need to be created and manipulated through the design process.
- 6. Figure 1. Vector-based graphic: the image itself on the left and the actual lines that make up the drawing on the right.
- 7. Working with Vector Graphics Outlines and Lines Lines and outlines in object graphics can assume any color. You can also specify how thick the lines should be, the style of the lines (solid, dotted, etc) and the shape of the corners (curved, squared, etc).
- 8. Fill Curved and closed objects can be filled with colors, color shifts and patterns. The colors are expressed numerically in terms of the ink coverage required for the respective printing inks. You can select fill patterns and color shifts from a predetermined menu.
- 9. Patterns A pattern consists of a small group of objects repeated in a square pattern. It is easy to make your own patterns. Gradients Color shifts are transitions among several colors at set distances. Gradients can either be linear or circular
- 10. Compound Path (Knockouts) Also known as knockouts, A curve that is placed within a closed object – a star within a square, for example – can be selected as a knockout. In this example, the selection means that a star knocks out a transparent hole in the square. As a result, whatever you put behind the square will be visible through the star hole.
- 12. Applications for Object Graphics Object graphics are created in illustration software such as Adobe Illustrator Adobe Streamline is one example. They are usually used to convert pixel-based logotypes into object graphics so they can be used in all possible sizes. Object graphics are usually saved in the image format Encapsulated Postscript (EPS). You can also save them in whatever format the software uses, but then the object may not be able to be placed in a page layout application.
- 13. Raster Graphics Raster graphics also known as bitmap images are made of individual dots called pixels that are arranged and colored differently to form a pattern. The individual squares that make up the total image can be seen when zoomed in. However, from a greater distance the color and shape of a bitmap image appear continuous. Since each pixel is colored individually, you can easily work with photographs with so many colors and can create photo-realistic effects such as shadowing and increasing color by manipulating select areas, one pixel at a time. Pixel Graphics Digitalized photographic images consist of tiny squares of a color, called pixels. The eye cannot perceive the pixels unless the image is greatly enlarged.
- 14. Bitmap programs are ideal to retouch photographs, editing images and video files and creating original artwork. Variety of changes to photographs can be made, such as adjusting the lighting, removing scratches, people, and things, swapping details between images, adding text and objects, adjusting color, and applying combinations of special effects.
- 15. Working with Graphics When photographs or illustrations are scanned into a computer, pixel-based images, or pixel graphics, are created. Another term of pixel is raster. A pixel graphic is a divided into tiny squares of color, almost like a mosaic. These tiny squares of color are referred to as pixels. Pixel graphics can also be created directly in the computer or by a digital camera.
- 16. Resolution If you assume that a pixel-based image is printed in a certain size, the image will consist of a certain number of pixels per centimeter or per inch (ppi). The resolution of an image is measured in ppi. This refers to the number and size of the pixels that make up a particular image. Sometimes the unit dpi is used (incorrectly) instead of ppi. Dpi, which means dots per inch, is the unit used to describe the output resolution in printers.
- 17. If the resolution of an image is low, the pixels will be large, and you will clearly see that the graphic consists of a mosaic-like pattern. At a higher resolution, however, the eye cannot perceive that the image is made up of pixels. There is an appropriate high-level resolution for most images; if you make the resolution higher than that, you will not get a better quality image but it will take up more storage space Image Resolution A pixel-based image always has a set resolution (pixels per inch, or ppi). In the example, the image has 8 pixels/0.0228 inches = 350 pixels per inch, or 350 ppi.
- 18. Color Modes, Channels and Bit Depth Bit Depth o For now, I believed that you have a better understanding of what is object and pixel graphics. As to let you know, in vector-based programs, such as Adobe Illustrator and CorelDraw Graphics Suite, the drawing tools make shapes based on mathematical formulas. o As to recap, vector objects have smooth lines and continuous colors even when you magnify the image. Vector drawings are resolution independent, meaning that when print a vector-based drawing, the quality depends only on the resolution of the printer.
- 19. A vector drawing looks the same whether viewed at its actual size or magnified.
- 20. In pixel-based programs, such as Photoshop, images are made up of tiny pixels that are arranged and colored to form a pattern. Each pixel represents a color. When you view a pixel-based image at its intended size and resolution, the colors and shapes appear smooth, but if you magnify the image, tiny individual squares become more evident. You can edit a pixel-based image pixel by pixel, and pixel- based images depend on the resolution at which they are saved for quality when printing the image.
- 21. Color depth sets how many colors are available in each pixel. The number of colors available in a pixel can range from two colors to millions. A pixel-based image looks smooth at its actual size but shows its pixels when magnified.
- 22. A color mode determines how the channels in each pixel create the colors in an image. And each channel in a pixel represents a primary color. Typically, color information is saved in a measurement called bit depth or color depth. This color depth measures how much color information is available in each pixel. The more bit depth that an image has, the more colors are available. More color depth translates to more accurate representation of color on-screen as well as on the printed page. Typical color depth values are 1-bit, 8-bit, 16-bit and 24-bit. For instance, a pixel with a 1-bit color depth has two possible color values – black and white. An 8-bit pixel has 256 possible color values and a 24-bit pixel has about 16 million possible color values.
- 23. Channels Every image you create in Photoshop contains channels. Channels store an image’s color information. Each pixel in an image can have as few as one and as many as four channels. The number of channels in an image depends upon the color mode in which the image is set.
- 24. To view the channels in a color image, use the Channels palette to display the image’s channels. Click on one of the channels to display only that channel. Clicking RGB would restore the full channel display). A special grayscale channel that is used to save selections is known as an alpha channel.
- 25. Color Modes A color model is a scheme used to break colors down into their component primary parts. Color models are used to represent color in images in a standardized way. In Photoshop, color models are applied to images as color modes. Photoshop supports eight color modes: Bitmap, Grayscale, Duotone, Indexed Color, RGB, CMYK, Lab and Multichannel.
- 26. Any image can be converted to or edited in any one of the eight color modes. To convert an image to another color mode, choose Image > Mode and select a color mode from the submenu The different color modes contain a different number of channels. Table 1 shows the number of channels per mode.
- 27. Table 1 The Number of Channels in a Color Mode One Channel Three Channels Four Channels Bitmap RGB CMYK Grayscale Lab Duotone Multichannel Indexed Color
- 28. If you want to convert an image to a color mode that is unavailable on the submenu (unavailable options are grayed out), you need to convert the image to another color mode before converting it to the desired color mode. For instance, if you want to convert an RGB color image to Bitmap mode, you have to convert the image to Grayscale first. You will learn more about the various color modes in the later chapters
- 29. The Various File Types and its Characteristics Pixel-based images can be saved in a number of file formats. Some of them have more or less becomes industry standards. They are primarily differentiated by which color modes they can handle as well as the level of features they are capable of.
- 35. The most common image file formats are Photoshop, EPS, TIFF, PICT, GIF and JPEG. Some are only used on Macintosh and others only on Windows. The two formats generally used in graphic production are TIFF and EPS.