Working with Raster Images In This Chapter 20 With AutoCAD® you can add raster images to your ■ Attaching and scaling raster image files vector-based AutoCAD drawings and then view and plot ■ Tuning image performance the resulting file. There are a number of reasons for ■ Managing images ■ Clipping images combining raster images with vector files, including ■ Accessing images from the scanning documents, faxes, or microfilm drawings; Internet ■ Controlling image brightness, using aerial and satellite photographs; using digital contrast, and fade photographs; creating effects such as watermarks and ■ Managing image support preferences logos; and adding computer-rendered images. 727 Using Raster Images in Drawings Raster images consist of a rectangular grid of small squares or dots known as pixels. For example, a photograph of a house is made up of a series of pixels colorized to represent the appearance of a house. A raster image references the pixels in a specific grid. Raster images, like many other AutoCAD drawing objects, can be copied, moved, or clipped. You can modify an image with grip modes, adjust an image for contrast, clip the image with a rectangle or polygon, or use an image as a cutting edge for a trim. The image file formats supported by AutoCAD include the most common for- mats used in major technical imaging application areas: computer graphics, document management, engineering, mapping, and geographic information systems (GIS). Images can be bitonal, 8-bit gray, 8-bit color, or 24-bit color. Several image file formats support images with transparent pixels. When image transparency is set to on, AutoCAD recognizes those transparent pixels and allows graphics in the drawing area to “show through” those pixels. (In bitonal images, background pixels are treated as transparent.) Transparent images can be gray-scale or color. Although the file extension is listed in the following table, AutoCAD determines the file format from the file contents, not from the file extension. 728 | Chapter 20 Working with Raster Images Supported image file formats Type Description and versions File extension BMP Windows and OS/2 bitmap format .bmp, .dib, .rle CALS-I Mil-R-Raster I .gp4, .mil, .rst, .cg4, .cal FLIC FLIC Autodesk Animator Animation .flc, .fli GeoSPOT GeoSPOT (BIL files must be .bil accompanied with HDR and PAL files with correlation data, in the same directory) IG4 Image Systems Group 4 .ig4 IGS Image Systems Grayscale .igs JFIF or JPEG Joint Photographics Expert Group .jpg or .jpeg PCX Picture PC Paintbrush Picture .pcx PICT Picture Macintosh Picture .pct PNG Portable Network Graphic .png RLC Run-Length Compressed .rlc TARGA True Vision Raster-Based Data Format .tga TIFF Tagged Image File Format .tif or .tiff Attaching and Scaling Raster Images Images can be referenced and placed in drawing files, but like external refer- ences (xrefs), they are not actually part of the drawing file. The image is linked to the drawing file through a path name. Linked image paths can be changed or removed at any time. By attaching images using linked image paths, or by dragging images using AutoCAD DesignCenter™, you can place images in your drawing and only slightly increase the drawing file size. See “Using AutoCAD DesignCenter to Attach Raster Images” on page 505. You can also access image files from the Internet by specifying a URL. See “Access- ing Raster Images Using the Internet” on page 743. Attaching and Scaling Raster Images | 729 Once you’ve attached an image, you can reattach it multiple times, treating it as if it were a block. Each insertion has its own clip boundary and its own settings for brightness, contrast, fade, and transparency. You can specify the raster image scale factor when you attach the image so that the scale of the geometry in the image matches the scale of the geometry in the AutoCAD drawing. AutoCAD multiplies the image by the specified scale. The default image scale factor is 1, and the default unit for all images is “Unitless.” The image file can contain resolution information defining the dots per inch (DPI), relating to how the image was scanned. If an image has resolution information, AutoCAD combines this information with the scale factor and the AutoCAD unit of measurement of the drawing to scale the image in your drawing. For example, if your raster image is a scanned blueprint on which the scale is 1 inch equals 50 feet, or 1:600, and your AutoCAD drawing is set up so that 1 unit represents 1 inch, then in the Image dialog box under Scale, select Specify On-Screen. To scale the image, you clear Specify On-Screen, and then enter 600 in Scale. AutoCAD then attaches the image at a scale that brings the geometry in the image into alignment with the geometry in the drawing. If no resolution information is defined with the attached image file, AutoCAD calculates the image’s original width to be one unit. After attaching, the image width in AutoCAD units is equal to the scale factor. To attach and scale an image 1 From the Insert menu, choose Raster Image. 2 In the Select Image File dialog box, select a file name from the list or enter the name of the image file in the File Name box. Then choose Open. 730 | Chapter 20 Working with Raster Images 3 In the Image dialog box, use one of the following methods to specify insertion point, scale, or rotation: ■ Choose Specify On-Screen to use the pointing device to insert the image at the location, scale, or angle you want. ■ Clear Specify On-Screen and enter values under Insertion Point, Scale, or rotation. To view the unit of measurement for the image, choose Details. 4 Choose OK. Command line IMAGEATTACH Related IMAGE displays the Image dialog box, from which you can manage your attached images. Tuning Image Performance Manipulating large or many small raster images can make severe demands on system performance. AutoCAD provides a variety of tools that help you work with and manage your image information. For example, if performance slows when you use the Clipboard, you can unload the raster image or turn off the layer containing the image before using the Clipboard. Changing the Temporary Swap File Location AutoCAD uses a special temporary image swap file to reduce the amount of RAM occupied by images. The Windows temp directory is the default location of the temporary swap file. You can specify a different directory by adding an entry under Temporary Drawing File Location on the Files tab in the Options dialog box. See OPTIONS in the Command Reference. Tuning Image Performance | 731 Using Tiled Images Tiled images are small portions (a series of tiles) of large images that load much faster than nontiled images when using AutoCAD. If you edit or change any properties of an image, AutoCAD regenerates only the modified portion, thus improving the regeneration time. TIFF (Tagged Image File Format) is the only tiled format that AutoCAD supports. The TIFF reader supports all image types: ■ Bitonal (1 bit per pixel) ■ Gray scale and indexed color (8 bits per pixel) ■ True Color (24 or 32 bits per pixel) You can save tiled TIFF images with most image scanning tools. The image tiles should be no smaller than 64 × 64 pixels and no larger than 512 × 512 pixels. Additional file readers that support other tiled formats, such as CALS Type II, are available from third-party developers. Loading and Unloading Images You can improve performance by unloading images when you do not need them in the current drawing session. Unloaded images are not displayed or plotted; only the image boundary is displayed. Unloading an image does not alter its link. If memory is not sufficient to open multiple attached images in a drawing, AutoCAD automatically unloads images. In the Image Manager dialog box, you can use Reload to reload an unloaded image or to update a loaded image by reloading the image from the specified directory path. If a drawing is closed after an image is unloaded, AutoCAD does not load the image file when the drawing is next opened; you must reload it. To unload or reload images 1 From the Insert menu, choose Image Manager. 2 In the Image dialog box, select the image, and then choose Unload or Reload. or Select the image name, and then double-click on the status to immediately change the image’s status either from Unload to Reload or from Loaded or Reload to Unload. The status of the selected image changes. 3 Choose OK. All instances of the selected attached images are unloaded or reloaded. Command line IMAGE Shortcut menu Select an image to load or unload, right-click in the drawing area, and choose Image ➤ Image Manager. 732 | Chapter 20 Working with Raster Images To display specific image instances 1 From the Modify menu, choose Properties. 2 Select the images you don’t want to display. 3 In the Properties window, select Yes or No in the Show Image list. Shortcut menu Select an image, right-click in the drawing area, and choose Properties. Detaching Images You can detach images that are no longer needed in a drawing. When you detach an image, all instances of the image are removed from the drawing, the image definition is purged, and the link to the image is removed. The image file itself is not affected. To detach an image 1 From the Insert menu, choose Image Manager. 2 In the Image dialog box, select the image name. 3 Choose Detach. The image is no longer linked to the drawing file, and all instances of the image are removed from the drawing.