Understanding Adobe Photoshop: Digital Imaging Concepts and Techniques

2017-07-07 02:10:07

While it may come as a surprise to some of the people reading this book, not all cameras are digital. Shooting on film is still a very valid choice. Film offers greater flexibility for low-light situations, as well as offers some aesthetic options not afforded by digital. Many purists swear that shooting film adds richness in detail and color, as well as the introduction of subtle nuances like film grain, which cannot be replicated with a digital camera. Additionally, many pictures that you'll need to work with may exist on traditional media (such as prints) or as a negative. You'll need to use a scanner to turn these optical formats into digital formats.

Tip: Keep Your Images Organized on Your Computer

To manage your digital photo collection you have several options. Photoshop CS2 includes an application called Bridge that works efficiently to search and organize images. Additionally, I find that iPhoto works well for the Mac (and its bundled with most machines or part of the $49 iLife suite). You can also modify iPhoto's preferences so double-clicking a photo opens it in Photoshop. For PC users, be sure to check out Photoshop Album for its convenient cataloging abilities.

Choosing a Scanner

If you are in a computer lab or work environment, your choice in scanners may have already been made for you. However, it is still important to understand the different types of scanners that are available to consumers.

Flatbed Scanners

The most common scanner type is a flatbed scanner. Photos are loaded, face down, on a piece of glass. The scanner then moves a chargecoupled device (CCD) across the image to capture/digitize the image. High-quality scans can greatly increase the amount of data that is captured. As such, be sure to look at high-speed scanner-to-computer connection options. For a modern computer, FireWire or USB 2 are the best options. Do not get too bogged down with scanner attachments. Unless you only occasionally need them, slide adapters and transparency adapters don't work as well as a dedicated specialized scanner. These options often just add to the cost of the scanner. Be sure though to pay close attention to the optical resolution of the scanner; this is the maximum size of the image before software interpolation to enlarge it. Most users doing intermediate-level work, or desktop publishing, find a scanner capable of 600 to 1200 SPI to be adequate. Remember, samples per inch can translate fairly well into pixels per inch. It is a good idea to have more pixels to start with, and size the image down for delivery.

Note: LPI versus PPI

The general rule is to take your LPI requirement and multiply by two. Round up to the nearest large number and you have your PPI requirements.

Common PPI Requirements for Final File

Output Method	Typical PPI
Onscreen	7296
Screen Printing	100150
Laser Printing	150250
Newsprint	120170
Offset Printing	250300
High-Quality Offset Printing	300600

Film/Slide Scanners

Specialized scanners load in slides or film negatives. These scanners use a tray to hold the material, and then a motor pulls the tray slowly across an optical sensor. This process is relatively slow due to the resolution needed. The scanner must capture a lot of data from a very small surface area in order to produce a usable image. These scanners are slightly more expensive than flatbed scanners, but are essential if you work with slides or negatives frequently.

Tip: Multifunction Units

Many people purchase all-in-one units to save space and money. These combo machines can offer scanning, printing, photocopy functions, and faxing abilities. Do not ignore these units, as they can be great space-savers. Do realize, though, that if part of the unit breaks, you may be faced with a higher replacement cost. Consider an extended warranty, especially if you are a heavy user.

Drum Scanners

When top image quality is a must, pros turn to drum scanners. These units are very expensive (starting at $5,000 and going upsignificantly). This scanning technology is the oldest. It calls for the image to be mounted on a drum. This drum is then rotated in front of a photomultiplier tube. This tube is much more sensitive than the CCDs used in flatbed scanners. Drum scanners' primary advantage is resolution, and they should be used when you need to significantly enlarge a scanned image (such as museum archival pieces or for magazine output). Because the machines are expensive and very complex (as well as potentially destructive), users will often send images to a service bureau for drum scanning.

A drum scanner is a highly specialized piece of equipment. These machines are very expensive and are usually found only in high-end service bureau facilities.

What Size to Scan? Think in Pixels

People often get thrown when determining how big to scan. Too little information and the picture goes soft. Too much and you'll just slow the scanning down to a crawl. The answer is to know your intended output resolution as well as your device.

Purchasing Power

Shopping for a scanner can be a very confusing experience (which is usually made worse by the sales staff). Prices have plummeted in recent years as scanners have become more common. (Scanners used to cost so much that they would bundle in full copies of Photoshop to entice purchasers).

Be sure to keep the following in mind when looking to buy a scanner:

Does the scanner connect to my computer using a fast interface such as USB 2 or FireWire?

What is the optical resolution of the scanner? For example, 3000 pixels are enough to print a 10-inch image at 300 DPI.

Does the scanner support my computer's operating system?

Does the scanner come with a TWAIN plug-in that will allow Photoshop to see the scanner for direct import of images?

Does the scanner offer special features such as Digital ICE or a descreen filter for improving image quality?

For example, if you need to create a poster that is 20 inches wide and will be printed on a high-quality press requiring 300 PPI, use this calculation:

20 (inches) x 300 (PPI) x 1.25 (pad for flexibility) = 7500 pixels

Do not adjust the DPI (or PPI) settings of your scanner. Rather, crop the image after running a preview scan. You can then adjust the scanner's resolution by looking at the output size of the scanned file. As you adjust the output file size, the scanning software will automatically determine the appropriate settings for samples per inch. All scanners tell you just how many samples you are about to capture. Looking at these numbers gives you a truer sense of what you are really going to get. Total pixel count is much more important than DPI, especially when scanning images of various original sizes.

Troubleshoot your Scanner

Routinely check your manufacturer's Web site for new drivers. This software improves how well your scanner interfaces with Photoshop. The updates are generally free.

If your scanner malfunctions, power down your system and check your cable connections. When satisfied, power up the scanner first and restart your computer. If the problem is not fixed, check for new drivers.

Scanner Operation

It is safe to say that every scanner model is a little different. Hardware manufacturers must write software that allows the scanner to interface with your computer. When choosing a scanner, be sure it works with your computer's operating system (always check the box or manufacturer's Web site carefully).

Video Training

Scan, Crop & Straighten

1.	Before scanning an image, install the software and drivers needed by your scanner. These are usually included on a disc provided by the manufacturer or for download from its Web site.
2.	Ensure that the scanner is lying flat, or you may get misregistered scans.
3.	Place your photos on the scanner straight. Use the edges to help you maintain parallel edges on your photos. If you get crooked photos, try the new automation tool File > Automate > Crop and Straighten Photos (available in Photoshop CS or later). You'll find two Crop and Straighten demo files in the Chapter 3 folder.
4.	Run a preview scan first to check image placement and details.

5.	If your scanner allows you, set the white and black points before scanning. This is accomplished by making a preview scan, then using your scanner's software to identify a black and a white point in the image. You can then use Photoshop's color correction tools to adjust the white and black points as well as make additional color changes. Every scanning software program is different, so be sure to see the documentation included with the scanner or on the manufacturer's Web site.
6.	Scan slightly higher than the quality you need; for example, scan at 300 SPI for newsprint, even though you may only deliver it at 170 PPI. The extra pixel information will allow you to zoom in for further corrections. It also gives you extra pixels in case you need to crop the image.
7.	Save to formats such as TIFF (Tagged Image File Format, a standard in the print industry). This file is efficient for storage and supports Lossless compression to reduce file size. The Photoshop (PSD) format is great for layered files, but is not as efficient for single-layer files. Always save the appropriate file extension for your file type.

Tip: Capture More Than You Need

There's no need to overdo it, but I always recommend capturing two to three times more data then you will need. For example, if you are going to be outputting a Web graphic at 1024 x 768, you should capture at least 3000 x 2000 pixels to start. Having the extra pixel data will give you more details to work with when zooming in for touchup. It also allows for you to make decisions about cropping and reformatting.

Good Clean Fun

There is no quick fix for dirt or grime on an image once it's in Photoshop. With this in mind, make sure your scanner and images are clean before you scan.

1.	Make sure the scanner is clean. Use a gentle glass cleaner whenever smudges appear. Spray the cleaner on a soft cloth, and then wipe the scanner bed down. Let the scanner completely dry before placing photos on the glass.
2.	Make sure your photos are clean before scanning. Never write on the back of photos, instead write on a Post-it note and temporarily adhere it to the back.
3.	If scanning previously printed items (such as magazines, books, or inkjet prints) you will likely get a moiré pattern. This is manifested by visible dots and is caused by the scanner grid not lining up with the dot pattern of the original image. Try scanning at a higher resolution, and if that doesn't work, use the descreen filter in the scanning software. If this option is not available (or you can't rescan the picture), run Photoshop's Median filter at a low value (Filter > Noise > Median).

If you scan an item that has been previously printed, you'll often see a moiré pattern. To fix this problem, your best option is to go back to the original source, or turn on the descreen option in your scanner's software.