Do I really need to keep the photographs or negatives from a client job--since I've already scanned the images and have them saved with the rest--of the job files for any future changes?

Maybe not, but I'll answer that question by relating my experience. When I was at the university in the early '90's, my department handled most of the medical photography for the university and its various medical research facilities. This generated thousands of negatives a year for us to archive. We had a stash of over 50 years worth of medical photography negatives. We began to toss around the idea of scanning them to store digitially then converting some of our Nikons to digital to record the imagery in digital form from the get go.

Problem though is two fold:(1) No digital storage medium is as permanant as film. Proof is the fact that we have film stored for over 40 years that is still in good enough shape to make a print and/or re-archive. Hard drives we bought only five years ago are now dead or dying, tape backup is about as reliable over long periods of time as an 8-track tape, and optical storage systems once thought to be truly permanant have now been shown to begin substrate corruption after only a few years service.(2) Most digital storage medium mechanisms are bound in time technologically.

That is to say, if you standardize on DAT tape, whose to say that DAT tape will not go the way of QIC 20 format or 9 track format. The mechanism may not be available in the near future let alone the distant future. So to compensate for this many organizations develop elaborate redunancy policies regarding digital storage. This means that they get multiple copies of the image in digital form often on different types of storage systems. Redunancy and multiple mediums drastically increase the physical space requirements for image storage. In short, save the negatives.

The question I have is where do they come up with setting the-- LPI to 53, 83, and 106. Are these magic numbers or what?

Almost! The screen rulings (LPI) are based on a mathematical formula that takes into consideration, among other things, the occilation frequency of the video clock generator in the laser control circuit. What? Suffice it to say that the rulings are practically magical. As a matter of fact most screen frequencies and angles used in four color separating in more expensive imagesetters are arrived at with a great deal of secrecy because these little differences mean the world to those little color rosettes.

What exactly is the difference between a PICT (or other types of vector file formats) and a TIFF (or bitmap) file format?

For the most part they contain the same type data when it comes to bitmap information, that is each pixel in the image. But the PICT file specification (created by Apple and based on Quickdraw) can also contain vector data. Vector data is resolution independant. For example, instead of a series of pixels making up a line across an image in a bitmap, a vector line would be an x,y coordinate where the line starts and stops and then a value for its thickness and color.

As you can see the PICT file can be much more complex than a TIFF file and this is why Aldus (now owned by Adobe) along with Microsoft created the TIFF file specification. They needed a simple yet rich file type that could handle greyscale data from a scanned file and be exchanged between various machines and operating systems. TIFF is one of the most widely supported lossless bitmap file format to date. It is now capable of handling not only greyscale data but color data as well and even has the ability to store data in a lossless compressed form (LZW and Packbits in the 5.0 spec, CCITT IV and V, and JPEG/M-JPEG in the 6.0 spec). PICT currently has only one method for compressing a file, through the use of the Quicktime/Quickpress extension from Apple, this allows a PICT file to be stored as a JPEG lossy compressed file and read by any application without conversion first.-- Which format is best for a specific image (i.e. a simple B&W, a scaled-- image, a color image, etc.) It depends entirely on your situation. Remember, that more pleasing it is -- the more memory and the slower your system will be in manipulating them. In my opinion TIFF is the best file format for all of these examples mentioned. The basic TIFF file (5.0) can handle 1-bit, 4-bit, and 8-bit greyscale data, and can handle 8-bit, 16-bit, and 24-bit color data. The most common forms however are 1-bit and 8-bit greyscale, and 8-bit and 24-bit color. With the two basic forms of compression recognized in the TIFF spec you can successfully compress all of these types of images so that they take up less space in storage without worrying about using some secondary compression utility.

Why are there so many different DPI scales? What common laser printers-- use what DPI? What DPI do image-setters use? What DPI can PageMaker-- handle? MicroSoft Word? Quark? What about an Image Writer or a-- Stylewriter?

DPI or Dots Per Inch is a clever marketing tool that the early laserprinter manufacturers came up with that really doesnt mean a whole lot. A few years ago, imagesetter manufacturers and scanner makers were talking in the more descriptive SPSI (spots per square inch) and LPI (lines per inch) measurements. It was very common for imagesetters to produce 1.6 million SPSI at 133 LPI, or 1270dpix1270dpi with 256 grey scales. Marketing types couldnt compete because the laserprinter seemed paltry in comparison, 90,000 SPSI at 53 LPI, or 300dpix300dpi with 14 grey scales.

Anyway DPI has become dominant because laserprinter manufacturers had more advertising money. Most laserprinters are now showing their DPI uniformly anyway, so you can simply square the DPI and get an accurate SPSI. So DPIxDPI = SPSI which is much more useful in determining how much better one laserprinter is over another one.

For instance, the original Apple Laserwriter was 90,000 spsi (300x300), the NeXT Laserprinter is 160,000 spsi (400x400) which is 1.7 times better not 1.3 as the 400/300 ratio would suggest. Where this really gets interesting is with the new crop of 600dpi lasers. For instance, the new QMS 860 is 360,000 spsi, or 4 times better not 2 times as the 600/300 ratio would suggest. Below is a list of some common printers at the turn of the century and their SPSI:

Printer                     SPSI                    Type
-------------------------------------------------------------------------	

Epson LX-80                 14,400          9-pin Dot Matrix
Apple Imagewriter           20,760          18-pin Dot Matrix
Apple Laserwriter           90,000          Canon CX Laserprinter
HP LaserJet III             90,000          Canon SX Laserprinter
Panasonic KXI1124          129,600          24-pin Dot Matrix
Canon BJ200e               129,600          Canon 36-valve Bubble Jet
NeXT Laserprinter          160,000          Fujitsu Laserprinter
Dataproducts LZ960         160,000          Fujitsu Laserprinter
Compaq PageMarq 20         320,000          Xerox Laserprinter
HP LaserJet IV             360,000          Canon BX Laserprinter
Lasermaster L1000          600,000          Fujitsu Laserprinter
Linotronic 170           1,612,900          Infrared Laser imagesetter
Linotronic 330          11,444,689          Helium Neon Laser imagesetter

AGFA SelectSet 5000     21,622,500          Helium Argon Laser 
imagesetter

What are the best ways (if any) to compress a graphics file once its-- been scanned?

The TIFF format provides a Compressed TIFF version -- that is usually recognized anytime that Uncompressed TIFF is. Other formats can be manually compressed -- but will need to be manually uncompressed anytime you need them. Manual compression is used more for archiving the file for storage and can save a significant amount of space.

Without loosing any of the data, most forms of compression are based on For inthe LZH (Lempel-Zimpel-Huffman) algorithm, they are:

For the Mac: Stuffit CompactPro

For the PC: PKZip ARJ LHA

For UNIX Machines; Unix Compress gzip

They are all good and most will compress a file within 5-10% of the other.

My Hewlett-Packard ScanJet came with a rudimentary scanning package.-- Is there better scanning software than DeskScan? What are the main-- features to look for in scanning software?

Concensus favorite for professional scanning and retouching these days is still Adobe PhotoShop. Look especially for software that gives you the ability to scan and save in all the common file formats that you will want to use, and your scanning software should definitely allow you to crop and rotate before or during saving. Your scanner should also have a TWAIN (Technology Without An Interesting Name) module. TWAIN is an interface supported by many applications these days and allows you to preform scanning inside of usually non-image processing packages such as Adobe Creative Suite Apps, Office Applications, etc.

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