Help Desk.How It Works.Page Eight

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Laser and Ink Jet Printers

Although there are hundreds of different printers on the market, on this page we'll only look at the two most common types used today: Color Ink Jet Printers, and Black and White Postscript Laser Printers.

As their names imply, ink jet printers create an image on paper by using a jet to spray colored inks in a specific pattern. In short, they "spit" liquid ink at the paper. Although the ink may smear when wet, newer types of ink are fairly permanent when fully dry.

Laser printers, one the other hand, use a more complex process that involves tiny particles of powdery dry "toner." A laser beam creates a positive electrical charge on certain areas of the paper, which attracts and holds negatively charged toner particles ONLY in those areas. Then, the whole page runs through a "fuser" assembly which applies heat and pressure to permanently bond the toner particles to the paper.

Because of the complexity of how printers work, there's not much you can do to fix them if they malfunction. Just keep them clean and dust-free, use a gentle hand when operating them, and replace the toner or ink cartridges as often as needed (Always follow the directions in your printer's owners manual carefully). If you do these few things faithfully, your printer should provide many years of excellent service.

Understanding Printer Resolutions: The "resolution" of your printer is the maximum number of individual ink or toner dots the printer is capable of printing in one square inch of paper. Most modern laser printers can print a grid that measures 600 dots wide by 600 dots high (measured in dots per inch, or "600 dpi"). More expensive laser printers can produce 800, 1200 or even 1800 dpi resolutions. The higher the number, the finer the detail in your printed images.

Most older ink jet printers used a grid that measured 360 dots wide by 360 dots high. Modern ink jet printers have a resolution of 720 dpi. The most expensive models use an advanced technology to produce "half dots" and achieve an "apparent resolution" of 1440 dpi. (NOTE: Even a 1440 dpi ink jet printer cannot produce the image clarity of a 600 dpi laser printer due to the fact that ink jets "spray" ink on the paper, which always creates a very slight "overspray haze" around solid objects.)

Understanding Line Screens: Line screens were developed by commercial printers as a way to reproduce "continuous tone" photographic images. (The colors in a photograph blend together smoothly and evenly.)

Printing, however, is a mechanical process, in which continuous tone images are an impossibility. But, commercial printers discovered that they could make a printed image LOOK like a continuous tone image by printing a grid of tiny ink dots. When the ink dots were larger and closer together, they looked like a darker tone. When the dots were smaller and further apart, they looked like a lighter tone.

The easiest way to see this in action is to look at a newspaper. Most newspaper images are printed using a line screen of 65, 72 or 85 lines per inch ("lpi"). If you look at each image closely, you'll see that what appears to be various shades of gray are actually a pattern of larger and smaller solid-black dots. The same process is used to print images in consumer magazines. But, magazine printers use higher line screens (133 or 150 lpi) to create more detailed images. You'll have to look very closely, but you'll see that magazine images are also created using an arrangement of individual ink dots packed very closely together. (NOTE: In color images, the overlapping of the color dots helps to disguise the line screen pattern.)

Most modern printers are limited to creating a line screen from 85-110 lines per inch, based on their actual printing resolution. As an example, if a laser printer with a printing resolution of 600 dots (of toner) per inch is used to print an image at 60 lines per inch, we can assume that each individual dot in the final image will be created using a small grid of toner dots measuring 10 dots wide and 10 dots high.

Understanding Color Printing: Inside most color ink jet printers are FOUR liquid ink cartridges: Magenta (purplish red), Cyan (light blue), Yellow and Black. Almost any color you can imagine can be printed using a mixture of these four ink colors. (NOTE: Expensive color printers may use six or eight different ink colors to reproduce colors more accurately.)

When the computer sends a command to print one of these basic ink colors, the appropriate ink gets sprayed right on the paper. But, what happens when an image needs to be green? For this information, the computer looks at the printer's driver software and "color-matching" abilities. It might determine that - on this particular printer - the desired shade of green can be created using a spray of Cyan, a spray of Yellow, a touch of Magenta, and a smidgen of black.

Unfortunately, because computer printer inks are opaque, if you would spray each of these four colors in exactly the same place, you would only see the color that's on top of the pile (usually black). So, to compensate, the printer "offsets" the placement of each color by a fraction of an inch, so that in any one spot on the paper (a "line screen dot") you'll be able to see a little bit of all four colored inks (if all four are used to create that particular color.) Your brain mixes these four colors together and says, "That's Forest Green"! The amount of offset for each color is largely determined by the printer's resolution.

The amazing thing is that your printer needs to calculate the individual color ink mix and spray offset for each and every line screen dot in the image. That should obviously explain why the printer can print a whole page full of solid black text so much faster than even a small 4-color photographic image.

Understanding Postscript: Adobe's Postscript page description language, or a variation of it, is used by almost every laser printer to define exactly how the printed page should look. Postscript software is what allows laser printers to produce images with far more precision and accuracy than any ink jet printer can. Postscript is also the reason laser printers are more expensive than ink jets: they need to have an expensive microprocessor and RAM inside to translate the postscript commands.

Postscript software capabilities are also available on some of the better, more expensive ink jet printers through the use of RIP (Raster Image Processing) software. RIP software translates the Postscript commands using the computer's CPU (rather than the built-in processor found inside laser printers). Using RIP software may slow down both the computer's performance and the printing process substantially, but it allows any printer to produce a much finer and more accurate image.

How to Connect Your Printer: It's important to remember that all printers for PCs and Macs are exactly the same, except for how they connect to the computers. Knowing this, it's surprising that the prices often vary between the two versions.

Most home computer printers connect to your Mac using a standard Apple serial cable. A suitable cable should be included with the printer, but be sure to ask the salesman just in case. The advantage of a serial connection is fast, easy setup. Just plug one end of the cable into your printer, plug the other end into your Mac's printer (serial) port, and off you go.

The disadvantage of a serial connection is the slow data transfer speed from the computer to the printer. This isn't too much of a problem for older ink jet printers - which run very slowly - but it may become a factor with newer ink jet printers and all laser printers. To speed things up, you may want to consider a printer that has the ability to connect via an AppleTalk network connection.

Although you will have to purchase a separate network cable and network connectors for both devices, the increased printing speed and productivity should quickly make up for the additional expense. What's more, in a home or small office with two or more computers, a network connection can allow all users to share the same printer. That saves money in the long run! Most laser printers and some ink jet printers already have an AppleTalk connection port built in. If not, the manufacturer may sell an optional AppleTalk (LocalTalk) network interface for your printer.

At the top of the line for data transfer speed is an Ethernet connection. Ethernet ports are very rare on inexpensive ink jet printers (they may be available as an option), but are quite common on most laser printers. Add a simple Ethernet cable to your purchase and you will have the fastest data transfer speeds possible.

(NOTE: The single most common "printing problem" we are asked to repair in the field turns out to be nothing more than a loose printer cable connection. You can save yourself many hours of frustration by always checking your printer cable connections FIRST!)

Connecting Printers to the iMac and newer G3 Computers: Apple's new iMac,"2nd generation" G3 computers, and all future models now under development don't use traditional Macintosh serial (printer and modem) ports. Instead, these machines use Universal Serial Bus (USB), Ethernet and "FireWire" technology to communicate with printers and other external peripherals.

If this is your first computer purchase, you can buy a new printer that is specifically made to connect to an iMac or G3 model using USB or Ethernet. However, if you already own a high-quality ink jet or laser printer that's worth using for a few more years, you'll have to look at these options:

Check with your printer manufacturer to see if they offer a USB or Ethernet adapter for your model printer. (Note: These interface adapters can be quite expensive.)

Purchase an inexpensive (under $100) USB-to-Serial converter from your favorite retailer or mail order catalog. (Note: We like the products manufactured by Griffin Technologies.) These devices are compatible with both the iMac and the new G3 models.

Purchase a slightly more expensive (but still under $100) Serial PCI card (for the new G3 Macs only) which installs inside your computer and provides one or more (up to four) traditional Macintosh serial ports.

(NOTE: If you have an older ink jet printer, the best solution may be to replace it with a newer ink jet. Technology improvements in the past few years have dramatically improved ink jet print quality, software drivers, print speed and color accuracy, for a fraction of the old printer prices.)

About Printer Driver Software: To tell the computer exactly how to communicate with the printer, you will need to install the printer driver software that comes with the printer. It should only take a few minutes and is usually a problem-free process on the Mac.

(NOTE: Be sure to visit your printer manufacturer's web site every few months to see if updated driver software for your printer has been released. These updates usually fix bugs and problems that became apparent after the software was shipped.)

If you have an Apple ink jet printer, or almost any laser printer, you may not need to install printer drivers at all. The necessary driver software for all Apple ink jet printers are installed by the MacOS System Software. And, almost all Mac-compatible laser printers can use the built-in LaserWriter 8 software driver installed as part of the MacOS operating system. (NOTE: Read the directions that come with your printer to determine which printer drivers you should install.)

About the Print Monitor: In the Chooser application (which allows you to "choose" the printer you want to use) you will find controls to turn AppleTalk Networking On/Off (Keep if off when using a serial port connection. Turn it on for any network printer connection.)

In addition, you will find the controls to Enable/Disable background Printing. Most Mac-compatible printers have no problems printing in the "background" (so you can move on to other work while the printer does its job), but some less expensive printers have problems if printing takes place in the "background."

If you "enable" background printing, something quite amazing happens when you tell your computer to print a page. Instead of sending the document directly to the printer, the computer quickly "spools" the data to a holding area, then feeds it to the printer in the "background" at a more leisurely pace.

Your window to this "holding area" is the Print Monitor Application which is automatically activated any time you print a document. Using the Print Monitor (or similar monitoring applications installed as part of the software for your particular printer), you can track the progress of your printing, rearrange the printing order of multiple documents and receive important information when the printer has a problem.

It's important to remember these Print Monitor applications when your computer appears to be having printing problems. One of the most common printing problems on a Mac is the printing of complex documents that contain many graphics, type faces of colors. The document may be too large to fit into the Print Monitor's "holding area." Allocating more memory to the appropriate Print Monitor Application (located in the Extensions Folder inside your System Folder), and allocating more memory to your working application will often solve these simple printing problems.

About GX Technology and Desktop Printing: GX Printing WAS an attempt by Apple to improve certain printing functions. It failed to take off as expected and has since been discontinued. If you still use System Software versions 7.5-7.6, don't use the GX printing options.

As for Desktop Printing, it is still in use today, but we're not really sure why! After speaking with more than 300 Macintosh clients, we have yet to find a single person who actually LIKES or uses Desktop Printing.

For those who don't know, this technology allows you to print files by dragging document icons and dropping them on "virtual printer icons" located on the desktop. Most people simply tell the current application to "print" the current document, then close that document and move on. So, the ability of Desktop Printing is largely unnecessary.

Our advice is to use the Extensions Manager Control Panel to disable all of the Desktop Printing extensions. And, if you have ever discovered a GOOD reason to use Desktop Printing, please send us an email by clicking on the "mail" icon below.

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Help: How it Works: 8 of 9
Laser and Ink Jet Printers Although there are hundreds of different printers on the market, on this page we'll only look at the two most common types used today: Color Ink Jet Printers, and Black and White Postscript Laser Printers. As their names imply, ink jet printers create an image on paper by using a jet to spray colored inks in a specific pattern. In short, they "spit" liquid ink at the paper. Although the ink may smear when wet, newer types of ink are fairly permanent when fully dry. Laser printers, one the other hand, use a more complex process that involves tiny particles of powdery dry "toner." A laser beam creates a positive electrical charge on certain areas of the paper, which attracts and holds negatively charged toner particles ONLY in those areas. Then, the whole page runs through a "fuser" assembly which applies heat and pressure to permanently bond the toner particles to the paper. Because of the complexity of how printers work, there's not much you can do to fix them if they malfunction. Just keep them clean and dust-free, use a gentle hand when operating them, and replace the toner or ink cartridges as often as needed (Always follow the directions in your printer's owners manual carefully). If you do these few things faithfully, your printer should provide many years of excellent service. Understanding Printer Resolutions: The "resolution" of your printer is the maximum number of individual ink or toner dots the printer is capable of printing in one square inch of paper. Most modern laser printers can print a grid that measures 600 dots wide by 600 dots high (measured in dots per inch, or "600 dpi"). More expensive laser printers can produce 800, 1200 or even 1800 dpi resolutions. The higher the number, the finer the detail in your printed images. Most older ink jet printers used a grid that measured 360 dots wide by 360 dots high. Modern ink jet printers have a resolution of 720 dpi. The most expensive models use an advanced technology to produce "half dots" and achieve an "apparent resolution" of 1440 dpi. (NOTE: Even a 1440 dpi ink jet printer cannot produce the image clarity of a 600 dpi laser printer due to the fact that ink jets "spray" ink on the paper, which always creates a very slight "overspray haze" around solid objects.) Understanding Line Screens: Line screens were developed by commercial printers as a way to reproduce "continuous tone" photographic images. (The colors in a photograph blend together smoothly and evenly.) Printing, however, is a mechanical process, in which continuous tone images are an impossibility. But, commercial printers discovered that they could make a printed image LOOK like a continuous tone image by printing a grid of tiny ink dots. When the ink dots were larger and closer together, they looked like a darker tone. When the dots were smaller and further apart, they looked like a lighter tone. The easiest way to see this in action is to look at a newspaper. Most newspaper images are printed using a line screen of 65, 72 or 85 lines per inch ("lpi"). If you look at each image closely, you'll see that what appears to be various shades of gray are actually a pattern of larger and smaller solid-black dots. The same process is used to print images in consumer magazines. But, magazine printers use higher line screens (133 or 150 lpi) to create more detailed images. You'll have to look very closely, but you'll see that magazine images are also created using an arrangement of individual ink dots packed very closely together. (NOTE: In color images, the overlapping of the color dots helps to disguise the line screen pattern.) Most modern printers are limited to creating a line screen from 85-110 lines per inch, based on their actual printing resolution. As an example, if a laser printer with a printing resolution of 600 dots (of toner) per inch is used to print an image at 60 lines per inch, we can assume that each individual dot in the final image will be created using a small grid of toner dots measuring 10 dots wide and 10 dots high. Understanding Color Printing: Inside most color ink jet printers are FOUR liquid ink cartridges: Magenta (purplish red), Cyan (light blue), Yellow and Black. Almost any color you can imagine can be printed using a mixture of these four ink colors. (NOTE: Expensive color printers may use six or eight different ink colors to reproduce colors more accurately.) When the computer sends a command to print one of these basic ink colors, the appropriate ink gets sprayed right on the paper. But, what happens when an image needs to be green? For this information, the computer looks at the printer's driver software and "color-matching" abilities. It might determine that - on this particular printer - the desired shade of green can be created using a spray of Cyan, a spray of Yellow, a touch of Magenta, and a smidgen of black. Unfortunately, because computer printer inks are opaque, if you would spray each of these four colors in exactly the same place, you would only see the color that's on top of the pile (usually black). So, to compensate, the printer "offsets" the placement of each color by a fraction of an inch, so that in any one spot on the paper (a "line screen dot") you'll be able to see a little bit of all four colored inks (if all four are used to create that particular color.) Your brain mixes these four colors together and says, "That's Forest Green"! The amount of offset for each color is largely determined by the printer's resolution. The amazing thing is that your printer needs to calculate the individual color ink mix and spray offset for each and every line screen dot in the image. That should obviously explain why the printer can print a whole page full of solid black text so much faster than even a small 4-color photographic image. Understanding Postscript: Adobe's Postscript page description language, or a variation of it, is used by almost every laser printer to define exactly how the printed page should look. Postscript software is what allows laser printers to produce images with far more precision and accuracy than any ink jet printer can. Postscript is also the reason laser printers are more expensive than ink jets: they need to have an expensive microprocessor and RAM inside to translate the postscript commands. Postscript software capabilities are also available on some of the better, more expensive ink jet printers through the use of RIP (Raster Image Processing) software. RIP software translates the Postscript commands using the computer's CPU (rather than the built-in processor found inside laser printers). Using RIP software may slow down both the computer's performance and the printing process substantially, but it allows any printer to produce a much finer and more accurate image. How to Connect Your Printer: It's important to remember that all printers for PCs and Macs are exactly the same, except for how they connect to the computers. Knowing this, it's surprising that the prices often vary between the two versions. Most home computer printers connect to your Mac using a standard Apple serial cable. A suitable cable should be included with the printer, but be sure to ask the salesman just in case. The advantage of a serial connection is fast, easy setup. Just plug one end of the cable into your printer, plug the other end into your Mac's printer (serial) port, and off you go. The disadvantage of a serial connection is the slow data transfer speed from the computer to the printer. This isn't too much of a problem for older ink jet printers - which run very slowly - but it may become a factor with newer ink jet printers and all laser printers. To speed things up, you may want to consider a printer that has the ability to connect via an AppleTalk network connection. Although you will have to purchase a separate network cable and network connectors for both devices, the increased printing speed and productivity should quickly make up for the additional expense. What's more, in a home or small office with two or more computers, a network connection can allow all users to share the same printer. That saves money in the long run! Most laser printers and some ink jet printers already have an AppleTalk connection port built in. If not, the manufacturer may sell an optional AppleTalk (LocalTalk) network interface for your printer. At the top of the line for data transfer speed is an Ethernet connection. Ethernet ports are very rare on inexpensive ink jet printers (they may be available as an option), but are quite common on most laser printers. Add a simple Ethernet cable to your purchase and you will have the fastest data transfer speeds possible. (NOTE: The single most common "printing problem" we are asked to repair in the field turns out to be nothing more than a loose printer cable connection. You can save yourself many hours of frustration by always checking your printer cable connections FIRST!) Connecting Printers to the iMac and newer G3 Computers: Apple's new iMac,"2nd generation" G3 computers, and all future models now under development don't use traditional Macintosh serial (printer and modem) ports. Instead, these machines use Universal Serial Bus (USB), Ethernet and "FireWire" technology to communicate with printers and other external peripherals. If this is your first computer purchase, you can buy a new printer that is specifically made to connect to an iMac or G3 model using USB or Ethernet. However, if you already own a high-quality ink jet or laser printer that's worth using for a few more years, you'll have to look at these options: Check with your printer manufacturer to see if they offer a USB or Ethernet adapter for your model printer. (Note: These interface adapters can be quite expensive.) Purchase an inexpensive (under $100) USB-to-Serial converter from your favorite retailer or mail order catalog. (Note: We like the products manufactured by Griffin Technologies.) These devices are compatible with both the iMac and the new G3 models. Purchase a slightly more expensive (but still under $100) Serial PCI card (for the new G3 Macs only) which installs inside your computer and provides one or more (up to four) traditional Macintosh serial ports. (NOTE: If you have an older ink jet printer, the best solution may be to replace it with a newer ink jet. Technology improvements in the past few years have dramatically improved ink jet print quality, software drivers, print speed and color accuracy, for a fraction of the old printer prices.) About Printer Driver Software: To tell the computer exactly how to communicate with the printer, you will need to install the printer driver software that comes with the printer. It should only take a few minutes and is usually a problem-free process on the Mac. (NOTE: Be sure to visit your printer manufacturer's web site every few months to see if updated driver software for your printer has been released. These updates usually fix bugs and problems that became apparent after the software was shipped.) If you have an Apple ink jet printer, or almost any laser printer, you may not need to install printer drivers at all. The necessary driver software for all Apple ink jet printers are installed by the MacOS System Software. And, almost all Mac-compatible laser printers can use the built-in LaserWriter 8 software driver installed as part of the MacOS operating system. (NOTE: Read the directions that come with your printer to determine which printer drivers you should install.) About the Print Monitor: In the Chooser application (which allows you to "choose" the printer you want to use) you will find controls to turn AppleTalk Networking On/Off (Keep if off when using a serial port connection. Turn it on for any network printer connection.) In addition, you will find the controls to Enable/Disable background Printing. Most Mac-compatible printers have no problems printing in the "background" (so you can move on to other work while the printer does its job), but some less expensive printers have problems if printing takes place in the "background." If you "enable" background printing, something quite amazing happens when you tell your computer to print a page. Instead of sending the document directly to the printer, the computer quickly "spools" the data to a holding area, then feeds it to the printer in the "background" at a more leisurely pace. Your window to this "holding area" is the Print Monitor Application which is automatically activated any time you print a document. Using the Print Monitor (or similar monitoring applications installed as part of the software for your particular printer), you can track the progress of your printing, rearrange the printing order of multiple documents and receive important information when the printer has a problem. It's important to remember these Print Monitor applications when your computer appears to be having printing problems. One of the most common printing problems on a Mac is the printing of complex documents that contain many graphics, type faces of colors. The document may be too large to fit into the Print Monitor's "holding area." Allocating more memory to the appropriate Print Monitor Application (located in the Extensions Folder inside your System Folder), and allocating more memory to your working application will often solve these simple printing problems. About GX Technology and Desktop Printing: GX Printing WAS an attempt by Apple to improve certain printing functions. It failed to take off as expected and has since been discontinued. If you still use System Software versions 7.5-7.6, don't use the GX printing options. As for Desktop Printing, it is still in use today, but we're not really sure why! After speaking with more than 300 Macintosh clients, we have yet to find a single person who actually LIKES or uses Desktop Printing. For those who don't know, this technology allows you to print files by dragging document icons and dropping them on "virtual printer icons" located on the desktop. Most people simply tell the current application to "print" the current document, then close that document and move on. So, the ability of Desktop Printing is largely unnecessary. Our advice is to use the Extensions Manager Control Panel to disable all of the Desktop Printing extensions. And, if you have ever discovered a GOOD reason to use Desktop Printing, please send us an email by clicking on the "mail" icon below.
BACK		NEXT

HOME . SERVICES . HELP DESK . RESOURCES . WHY MAC . CREDENTIALS
Copyright 1998, 5-Minute Mac Consulting, Wampum, Pennsylvania, USA