Bitmap images

1. Bitmap images Photo editors Resizing bitmaps JPG file formats Vector images GIF file formats Why are there so many image file formats? Animated and transparent .gif’s Created by Sheila MacLeod Potter, working for the AITT, Acadia University What are the different image file formats? “Bits” and .bmp files Getting images from the web Resolution and Scanning

2. Bitmap images • ‘Bitmap’ refers to digital images which are composed of dots or pixels • In a bitmap image, the image file has to define the exact colour of every pixel in the image This bitmap image has been stretched so that the pixels which compose it are clearly visible.

3. Resizing bitmap images • The more pixels which compose an image, the larger its file size. • The number of pixels in an image can be increased in two ways • by making the image larger in a photo editor. Tell me more about photo editors! • by increasing the image resolution • One confusing thing about the term bitmap is that there is a windows image format (.bmp) which is also referred to as a ‘bitmap’. To avoid this confusion, some people use the term raster when referring to images composed of pixels. • Bitmap file formats include .jpg, .gif, .bmp, .tif, .wpg, .psd, etc. Why are there so many image formats? Why does the computer ask me about number of bits when I go to save my image as a bmp?

4. To see how this vector graphic retains its smooth outline, hit Esc and then zoom in to %400. To resume show, click F5. bitmap vector Vector images Vector images are not made up of dots. Instead, they are composed of shapes and lines. Vector shapes are defined by the direction of the line which runs around their perimeter. Vectors have several useful qualities: • they are infinitely scaleable • they usually have smaller file sizes than bitmaps • they are crisp and clear when printed Note that: vectors on screen appear pixilated because the computer screen is composed of pixels!

5. Why are there so many image file formats? There are almost as many image file formats as there are programs that work with images. There is a great deal of competition in the graphics world among companies trying to create the best artist’s tool. Companies like Adobe and Corel, for example, each have software packages for working with images, which do many of the same things, yet they each (Adobe Photoshop and Corel PhotoPaint) have their own image file format (.psd and .cpt). At one time, different image file formats could only be opened by the software in which each was created, however, today, most common packages will let you open other company’s formats. One practical reason for different formats is that each saves a slightly different set of information with the file.For example, .jpg is a compressed format (small files), in which the minimum information is saved. By comparison, .tif is uncompressed and can save more file information.

6. Image File Formats .jpgand .gifare the best formats to use for presentations and for the web because they are both compressed in file size. Uncompressed formats such as .tif are best for print, however, there are many other formats which you may come across: Other Bitmap formats: • .tif : uncompressed image format which is good for use in printed projects like pamphlets and posters. • .wpg: format used by Corel Presentations • .bmp: windows preferred image format (your wallpaper is a .bmp) • .psd: layered file format used in Adobe Photoshop • .cpt: layered file format used in Corel Photopaint Vector formats: • .cdr: CorelDraw format. MS PowerPoint often has difficulty reading this format. • .wmf: “windows metafile” format. this format is widely accepted by programs which use vectors, including MS PowerPoint, and Word. • .fla: animated vector file created in Macromedia Flash HOME

7. “handles” appear all around images in PowerPoint, and can be ‘clicked and dragged’ to enlarge or shrink the image, but this does NOT change the image’s file size or resolution. Photo Editors • although, images can be stretched, or cropped within PowerPoint, this does not alter their file size. • in order to crop an image so that parts are eliminated from the image file itself (and the file becomes smaller), a photo editor such as MS Paint, Corel Photopaint, or Adobe Photoshop must be used. similarly, when you stretch or shrink an image in PowerPoint, the file size is not effected. • Image file size must be changed in a photo editor by changing the resolution, cropping, or resaving in a compressed format such as jpg or gif HOME

8. JPG file format JPEG is a popular format for two reasons: • It keeps photographic images clear • It lets you adjust the amount of compression JPG format should be used for photographs which contain a lot of detail and thousands of colours JPG compression does change the way an image looks uncompressed (tif) file size = 152Kb slightly compressed (jpg) file size = 31Kb highly compressed (jpg) file size = 10Kb

9. GIF file format In a .gif image, the number of colours is reduced to 256 and then "runs" of same-colour pixels are encoded in a colour + number of pixels format. This makes a .gif file great for storing drawings that have lots of same-colour pixels. gif images are common on the web. What’s an animated gif or a transparent gif? GIF format should be used for diagrams or drawings which contain few colours If the image contains 256 colours or less, gif compression does not change the way it looks

10. Why does it ask me about the # of bits when I save my .bmp files? • The more colours in an image, the more bits are required to represent it digitally. • The best-looking images contain 16 million colours (this is known as RGB [Red Green Blue] mode) • Imagine a bitmap in RGB that is 400 by 400 pixels. Saving this image requires 24 bits per pixel for 160,000 pixels, or 480,000 bytes. • 480,000 bytes = 480 Kb which would take considerable time to download from the web • For the sake of comparison, an RGB .jpg containing the same number of pixels (400X400) might be as small as 5Kb.

11. Animated & Transparent gif.s What’s an animated gif? Animated gifs are also ‘.gif’ files, but they are actually composed of multiple gif images which cycle to give an animated effect. Animated gifs files are as big as the sum of the gif images which compose the animation. Why does this gif file look differently on my machine than it did on the web? Many photo editors will allow you to assign a “transparent colour” within a gif image. That’s why, when you download gif’s from the web, sometimes an ugly background colour appears when you open the gif in another program. The ‘transparent’ colour only looks transparent on the web!

12. Copying and Downloading images from the web There are two ways to get an image off the web. • copy and paste • save it Copy and Paste • copy the whole screen (PrtSc) • OR copy the active screen (Alt+PrtSc) • AND paste (Ctrl+V) directly into your document Save • Right Click, Save As • you can’t choose a file type, but you can give the file a new name

13. Image 1 inch 1 inch Resolution and Scanning Resolution:Image resolution is expressed in dots (or pixels) per inch (dpi). When scanning an image, the resolution you choose depends on the way that you intend to use the image, or how it will be displayed. Suggested Minimum Resolutions: • for use on the web and in presentations: 72 dpi • for print: 150-300 dpi If you are scanning an image for use on the web or in a presentation, you may wish to “blow-up” the image by scanning it at a resolution higher than 72 dpi. Computer screens display at 72 dpi, therefore, small images that are scanned at higher resolution will be displayed larger on the computer screen. image size = 1 X 1; resolution = 100dpi