| Exactly what is raster? | |
| A raster image or scan is a digital representation of the original document that is made up of a series of dots (pixels). The most common type of raster is binary. In a binary file, each pixel is designated to be either black or white (on or off). The pixels are arranged in rows (scan lines) and present a visual picture of the document. | |
 Representation of Pixels |
| I have heard the term resolution used when referring to scanning, what is this? | |
| Above, we talked about dots, pixels and scan lines. Resolution is the number of dots or pixels captured per inch of scanned image. While resolution can be virtually anything, typical resolutions are 200dpi (dots per inch), 400dpi and 500dpi. The higher the resolution, the greater the detail that is captured from the document and the smoother the image appears. A 400dpi scan represents each inch of the document with 400 pixels in each direction or 160,000 pixels (400x400) for each square inch. A 200dpi scan on the other hand will have only 40,000 pixels (200x200) representing the same square inch. To produce the best image, the resolution used to scan a document should be matched to the detail and in most instances, the condition of the document. |
| Does a higher resolution make the digital file larger? | |
| It certainly does. A binary scan is a 1 bit image. This means that it requires 1 bit of data to define each pixel. In the example above, the 400dpi scan will require 160,000 bits of data for each square inch of the document, while the 200dpi scan will require only 40,000 bits. A 400dpi scan is 4X the size of a 200dpi scan. This is the size for an uncompressed file. Typically, binary scans are saved in a compressed format such as TIFF Group 4. Compression algorithms can reduce the size of the scans by as much as 18 - 770 times. |
| How can I use a binary scan? | |
| A binary scan is essentially a digital photograph. It can be stored on disk, CD or DVD, it can be retrieved for viewing and printing. With proper software, the scan can also be edited. |
| How can I edit a binary raster scan? | |
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This usually requires additional software that is designed to edit the raster image. MicroStation V8 software does have the ability, as part of the reference file attachment, to crop and mask the raster scan.
Bentley I/RAS B is an excellent tool to use for editing raster files. I/RAS B integrates with MicroStation V8 and provides tools to edit, scale, warp and cleanup binary scans from within MicroStation. | |
 Original Binary Scan | |
 Same Scan After Editing | |
| Can I use this digital picture in conjunction with my CADD software? | |
| Yes. MicroStation V8 can use raster images in many formats as reference files. This feature of MicroStation V8 is part of the foundation software and does not require additional or third party software. Autocad has almost figured out how to handle raster images as Xrefs as well as MicroStation, but still requires a product such as Cad Overlay or RasterX to edit the raster files. Both MicroStation V8 and Autocad provide a means to import raster images into the CADD file, but this is not a recommended use of scanned images. |
| What is the advantage of using raster files with CADD? | |
| Raster files can be a valuable tool in preparing CADD drawings. For example, you might use a scan of an existing floor plan and then use the CADD program to add to or change a portion of the plan in Vector. This approach produces what is called a Hybrid CADD file. When this Hybrid file is plotted, it is often difficult to distinguish between the raster and vector portions. | |
 Hybrid Floor Plan | |
| What other ways can I use binary raster scans? | |
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One of the most popular ways to use this type of scan is to convert all of your existing paper documents to digital format. You can index these digital files with a database and then use a Document Management program to find, recall, view and print the files.
Another use is to attach each raster scan to a MicroStation V8 design file containing your company's title and border. This design file would then be stored under your normal filing procedure. When you call up the design file, your raster scan is attached as a reference file. |
| What if I have a black and white photograph I want to use? | |
| A black and white photograph is scanned to what is called a Grayscale or continuous tone file. This image is much larger than a binary scan because it requires 8 bits per pixel to define the different shades of gray. There is also a 4 bit Grayscale file. The 8 bit file defines 256 shades of gray while the 4 bit file can only define 16 shades of gray. The 8 bit file produces a much more detailed representation of the original. This type of file is typically used when scanning aerial photographs. |
| Can I use a Grayscale scan with my CADD program? | |
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Bentley Descartes provides an excellent means to utilize scanned Grayscale photographs. Descartes' Image Transform feature includes transformation (move, scale, rotate, mirror) and layout tools for this type of scanned image. Descartes' Image Register tools provides a set of dynamic interactive image and vector warping tools to geometrically correct images and vectors within a given coordinate system.
Grayscale photographs also provide an excellent approach for renovation or addition of an existing structure. Instead of drawing the existing elevations, take a picture and use the Grayscale scan as a background for vector information. This approach can provide many benefits to almost all disciplines. | |
 Grayscale scan with vector overlay |
| Can I display and use more than one aerial photo at a time? | |
| Yes. The MicroStation V8 reference file capability and Bentley Descartes both provide the ability to simultaneously use multiple 8 bit Grayscale files as well as binary and color files - all of differing resolutions - at the same time. Bentley Descartes provides tools to edit, transform, enhance, mosaic and georeference these files. File display and editing is accomplished at amazing speeds for these large raster files. |
| How large are Grayscale scans? | |
| 8 bit Grayscale scans are 8 times larger that a binary file scanned at the same resolution. We have provided a File Size Chart below to make it simple to determine file sizes for all types of scans. |
| What about scans of color photographs? | |
| Very large, very useful and until now rather difficult to work with. MicroStation Descartes provides the ability to work with 8 bit files (256 colors) and 24 bit color (16 million colors). MicroStation V8 reference file and Image Manager provide for display of 8 and 24 bit color files. These files are most often stored in compressed JPEG format or TIFF RGB. | |
 Color Aerial Photograph |
| Just how large can a color file be? | |
| The File Size Chart below will help you determine file sizes for uncompressed scans. As an example: a 4 x 4 inch, 200 dpi binary scan will be 80k, 8 bit Grayscale or color scan will be 640k and a 24 bit color scan will be 1,920k. |
| Does ComputerGraphics / Atlanta have the capability to scan all of these file types? | |
| Yes. ComputerGraphics / Atlanta has scanning capability for binary, Grayscale and Color from page scans to large format documents up to 40" wide by virtually any length. Files can be delivered in any of over 170 different file formats including all of the different TIFF compression formats. For engineering documents, we use ANAtech large format Eagle and SLI scanners exclusively in our operation. |
| What resolutions can CGA provide? | |
| Our scanners are capable of scanning images up to and including 1600 dpi. The typical resolutions requested are between 200 and 500 dpi. Some scans that will be used for precise mapping applications are scanned at 1000 dpi. |
| How quickly can I expect ComputerGraphics / Atlanta to return my scans? | |
| We have the capability to scan 1200 - 1500 large scale documents per day. Depending on workload, simple scans of single drawings can usually be returned the same day they are received. |
| What media can I expect the scans returned on? | |
| Our standard return media is ISO9660 Standard CD-ROM. We can also provide 100Mb ZIP disks and DVDs. |
| Last, but not least, how much would all of this cost me? | |
| ComputerGraphics / Atlanta has a $25.00 minimum order. This includes scanning, media and shipping. A typical "E" size 200 dpi binary scan will cost $2.75 each in quantities of less than 100. For other resolutions or quantities please call us for a price quote. |
| One last question. What other services does ComputerGraphics / Atlanta offer? | |
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Other than full size document scanning, we offer aperture card scanning, page scanning and complete CADD Vectorization of paper documents to MicroStation V8, Autocad and most other CADD systems. Aperture card scans are either 200 or 400 dpi in any of 170 different formats. Page scans are typically the same, however we are finding that more and more companies, and the Federal Government, are requesting Adobe Acrobat® PDF files.
ComputerGraphics / Atlanta provides complete scanning and imaging solutions. CGA is also a Bentley Authorized MicroStation Reseller. We use all of the Bentley MicroStation products on a daily basis in our scanning, imaging and vectorization work. |
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or Halftones |
= Size of Scanned Image in Bytes |
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256 Gray Levels or 256 Colors |
= Size of Scanned Image in Bytes |
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Millions of Colors |
= Size of Scanned Image in Bytes |
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ComputerGraphics / Atlanta
The Park at Fowler Crossing
645 Molly Lane, Suite 130
Woodstock, GA 30189
770.517.6126
800.272.5681
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