1. Computer Image Dr Jimmy Lam CAD for Fashion and Textiles

2. Working with bitmap images and vector graphics Computer graphics fall into two main categories--bitmap and vector. You can work with both types of graphics in Photoshop and ImageReady Understanding the difference between the two categories helps as you create, edit, and import artwork

3. About bitmap images Bitmap images--technically called raster images--are made up of a grid of dots known as pixels. When working with bitmap images, you edit pixels rather than objects or shapes. Bitmap images are the most common electronic medium for continuous-tone images, such as photographs or digital paintings, because they can represent subtle gradations of shades and color

4. About bitmap images 2 Bitmap images can lose detail when scaled on-screen because they are resolution- dependent, they contain a fixed number of pixels, and each pixel is assigned a specific location and color value. Bitmapped images can look jagged if they're printed at too low a resolution because the size of each pixel is increased.

5. About vector graphics Vector graphics are made up of mathematically defined lines and curves called vectors. This means that you can move, resize, or change the color of a line without losing the quality of the graphic

6. About vector graphics 2 Vector graphics are resolution- independent--that is, they can be scaled to any size and printed at any resolution without losing detail or clarity. As a result, vector graphics are the best choice for representing bold graphics that must retain crisp lines when scaled to various sizes (logos, for example).

7. Understanding image size and resolution Understanding the relationship between the pixel dimension of an image and its print resolution is key to producing high-quality images. The amount of detail in an image depends on its pixel dimensions, while the image resolution controls how much space the pixels are printed over. For example, you can modify an image's resolution without changing the actual pixel data in the image--all you change is the printed size of the image. However, if you want to maintain the same output dimensions, changing the image's resolution requires a change in the total number of pixels

8. Pixel dimensions equal document (output) size times resolution A. Decreasing the resolution without changing pixel dimensions (no resampling) B. Original dimensions and resolution C. Decreasing the resolution at same document size decreases pixel dimensions (resampling)

9. Pixel dimensions and image resolution The number of pixels along the height and width of a bitmap image is called the pixel dimensions of an image. The resolution of an image is determined by the number of pixels per inch (ppi) printed on a page. In Photoshop, you can change the resolution of an image. In ImageReady, the resolution of images is always 72 ppi, to optimize the images for online media

10. Pixel dimensions and image resolution 2 When printed, an image with a high resolution contains more, and therefore smaller, pixels than an image with a low resolution. Higher-resolution images can reproduce more detail and subtler color transitions than lower-resolution images because of the density of the pixels in the images. High-quality images often look good at any print size. You can't improve a lower-quality image by printing it at a high resolution. Changing the print resolution of an image simply makes each pixel larger, which results in pixelation- -output with large, coarse-looking pixels. Increasing the print resolution of an image doesn't add any pixel information to the image. You can make a low-resolution image look its best by picking a print size that makes the most of the pixels it has.

11. Pixel dimensions and image resolution 3 It's important to note that video files are displayed only at 72 ppi. Even if an image has a higher resolution than 72 ppi, when it's displayed in a video editing application, the quality may not look very good. Printing the same low- resolution image at different sizes A. Small print size B. Medium print size C. Large print size

12. Printer resolution Printer resolution is measured by the number of ink dots per inch (dpi) produced by all laser printers, including imagesetters. (See Preparing images for press).Preparing images for press Inkjet printers produce a microscopic spray of ink, not actual dots; however, most inkjet printers have an approximate resolution of 300 to 720 dpi (see Printing images to a desktop printer). Many inkjet printer drivers offer simplified print settings for choosing higher quality printing. To determine your printer's optimal resolution, check your printer documentationPrinting images to a desktop printer

13. Monitor resolution Image data are translated directly into monitor pixels. This means that when the image resolution is higher than the monitor resolution, the image appears larger on-screen than its specified print dimensions. Monitor resolution depends on the size of the monitor plus its pixel setting. For example, a large image (800-by-600-pixel dimension) shown on a 15-inch monitor would almost fill the screen, but on a larger monitor, the same image would take up less room on the screen, and each pixel would appear larger

14. Monitor resolution 2 When you are preparing an image for online display, pixel dimensions become especially important. You should make sure that the size of an image allows room for the Web browser window controls on smaller monitors

15. Changing image size and resolution Once you have scanned or imported an image, you may want to adjust its size. In Photoshop, the Image Size dialog box lets you adjust the pixel dimensions, print dimensions, and resolution of an image; in ImageReady, you can adjust only the pixel dimensions of an image. For assistance with resizing and resampling images in Photoshop, choose Help > Resize Image. This interactive wizard helps you scale your images for print or online media. Keep in mind that bitmap and vector data can produce different results when you resize an image. Bitmap data is resolution- dependent; therefore, changing the pixel dimensions of a bitmap image can cause a loss in image quality and sharpness. In contrast, vector data is resolution-independent; you can resize it without losing its crisp edges

16. Discussion What is the different between bit-mapped image and vector image? What are the relationships between file image sizes, screen image sizes and printer images sizes?