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Tips for Adobe Photoshop CS3, How to Pick an image resolution (Understanding Image Resolution)

asu — Tue, 08 Jul 2008 12:34:06 +0000

After you have the concept of resampling under your belt, how do you know what size you should be resampling to? How many pixels do you need? Here are your general guidelines:
Photos for your inkjet printer:
Inkjet printers are stochastic printing devices: That is, they use a series of droplets to replicate each pixel in your image, as shown in Figure 2-12. In theory, the optimal image resolution is ƒ1?3 of the printer’s rated resolution.
For example, a printer rated at 720 ppi works best with images at 240 ppi.
1,440 ppi printer, the formula calls for an image resolution of 480 ppi (and that goes for the 2,880 x 1,440 printers, too). However, most folks find that regardless of the printer’s rating, they never need an image resolution higher than 300 ppi.
Web images: Ignore resolution. Ignore the entire Document Size area of the Image Size dialog box. Consider only the image’s pixel dimensions. Determine what area of the Web page the image will occupy and then resize to exactly those pixel dimensions.
Page layout programs and commercial printing: If your image is to be placed into a page layout program’s document and sent to a commercial printing facility, you need to know the line screen frequency (the resolution, so to speak) of the printing press on which the job will be run. Ask the print shop or the person handling the page layout. Your image resolution should be either exactly 1.5 times or exactly twice the line screen frequency. (You shouldn’t notice any difference in the final printed product with either resolution.)
PowerPoint presentations and word processing documents: Generally speaking, 72 ppi is appropriate for images that you place into a presentation or Word document. You should resize to the exact dimensions of the area on the page or slide that the image fills.

Resolution Revelations

asu — Tue, 08 Jul 2008 12:14:44 +0000

In this wonderful world of digital imaging, you see resolution used in four basic ways:
Image resolution: Image resolution is the size of your image’s individual pixels when you print. I go into greater detail about this concept in the upcoming section, “Picking an image resolution.”
Camera resolution: Digital cameras capture each image in a specific number of pixels. Check your camera’s user guide or open one of the images in Photoshop and choose Image? Image Size. Take a look at the number of pixels that your camera records for the width and for the height. Multiply the numbers together, divide by one million, and round off the result. (If you’re in the camera maker’s marketing department, make sure that you round up.) That’s the megapixel (MP) rating for the camera. Use it as a general guideline when shopping. If you create Web graphics or snapshot-size prints, 3 or 4 MP is fine. For large prints, you need at least 6 MP.
Monitor resolution: Monitor resolution determines how many pixels are visible on-screen. Whether you use a Mac or a PC, you set the monitor resolution at the system level (as shown in Figure 2-4). When you use a higher monitor resolution, you get a larger workspace, but each pixel is smaller, which might make some jobs tougher. Experiment to find a monitor resolution that works just right for you.
Mac: Click the blue Apple menu in the upper-left corner of the screen and choose System Preferences. Then click Displays. (Some Apple monitors have a button on the bezel that automatically opens the window for you.)
Windows: Choose Start?Control Panel and then double-click Display. Click the Settings tab to see what monitor resolutions are available.
Printer resolution: Unlike the three preceding terms, printer resolution doesn’t involve pixels. Rather, a printer resolution tells you how many tiny droplets of ink are sprayed on the paper. Remember that it takes several droplets to reproduce a single image pixel — you certainly don’t need an image resolution anywhere close to the printer’s resolution!
(See the following section for more on this.)

Formats for digital photos (Tips For Adobe Photoshop CS3)

asu — Sun, 15 Jun 2008 12:13:58 +0000

If you print your images yourself at home or the office, you can stick with the original format or use the PSD Photoshop format. If you send the photos to the local camera shop (or discount store) for printing, stick with JPEG — or, if they accept it, TIFF. Here are the pros and cons of the major formats that you should consider for photos:

PSD: Photoshop’s native file format is great for saving your images with the most flexibility. Because the PSD format supports all of Photoshop’s features, you don’t need to flatten your images — and keeping your layers lets you make changes later. If your file size is very large (4MB or larger), make a TIFF or JPEG copy before printing, flattening all the layers. Don’t send PSD files to the local shop for prints.

TIFF: Although the TIFF file format (as you use it in Photoshop) can save your layers and most other Photoshop features, make sure to choose Layers Flatten Image before sending files out for printing. Layered TIFF files generally are compatible only with programs in the Creative Suite. If you don’t flatten the image prior to saving as TIFF or if you elect to include layers when saving as TIFF, Photoshop presents you with a gentle reminder.

JPG: JPEG, as it’s called, is actually a file-compression scheme rather than a file format, but that’s not important. What is important is that JPEG throws away some of your image data when it saves the file. Save important images in PSD or TIFF and use JPEG only for copies. When should you use JPEG? When sending images to a photo lab that doesn’t accept TIFF files and when sending images (perhaps by e-mail or on CD) to people who don’t have Photoshop. Unlike PSD and TIFF, you can open JPEG images in a Web browser and print from there — and so can Granny, and Cousin Jim, and that overseas soldier you adopted. When saving JPEGs, the lower the Quality setting you choose in the JPEG Options dialog box, the smaller the file but also the more damage to the image. I discuss saving as JPEG in more detail in the sidebar, “Resaving images in the JPEG format.”

PDF: It’s easy to overlook Adobe’s PDF format when talking about photos, but you should consider using this format. Although the local photo lab probably won’t accept it, it’s a great format for sharing your pictures with folks who don’t have Photoshop. Unlike JPEG, your images won’t be degraded when saving as PDF; and like JPEG, just about anyone with a computer can view the files. (Adobe Reader, which you can use with PDFs,
is found on just about every computer now, just like Web browsers for JPEG.) Keep in mind, however, that PDF files are larger than JPEGs.

Large Document Format (PSB): Really, really, really big pictures over 30,000 pixels wide or long or both need to be saved in the PSB file format. Will you ever need this format? Consider that 30,000 pixels at a
photo-quality resolution of 300 ppi is 100 inches long. At a resolution of 85 ppi, more appropriate for a long banner to hang in a hallway, you’re talking about artwork that stretches almost 30 feet! Can your printer do that? If not, you probably don’t need the PSB file format. You could theoretically use a number of other available formats, such as DCS, PNG, and Photoshop Raw, but there’s no real need with the more common and more versatile formats about which you just read.

If you’re working with photos from your digital camera and you want to save them as JPEG but that format isn’t available in the Save As dialog box, convert the image to 8-bit color with Image > Mode > 8-Bits/Channel. If you shot the image in Raw (or TIFF) and need to save as JPEG, you’ll have to convert to 8-bit color because JPEG doesn’t support 16-bit color.