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.increases the file size and slows the printing of theimage; furthermore, the device will be unable toreproduce the extra detail provided by the higherresolution image.Monitor resolution The number of pixels or dotsdisplayed per unit of length on the monitor,usually measured in dots per inch (dpi).Monitorresolution depends on the size of the monitor plusits pixel setting.Most new monitors have aresolution of about 96 dpi, while older Mac OSmonitors have a resolution of 72 dpi.Understanding monitor resolution helps explain72-ppi and 300-ppi images; inset zoom 200%why the display size of an image on-screen oftendiffers from its printed size.Image pixels are trans-lated directly into monitor pixels.This means thatwhen the image resolution is higher than themonitor resolution, the image appears largeron-screen than its specified print dimensions. CHAPTER 294Getting Images into Photoshop and ImageReadyFor example, when you display a 1-by-1 inch, output devices, a lower resolution can produce144-ppi image on a 72-dpi monitor, it appears in a good results.To determine your printer s screen2-by-2 inch area on-screen.Because the monitor frequency, check your printer documentation orcan display only 72 pixels per inch, it needs consult your service provider.2 inches to display the 144 pixels that make up oneNote: Some imagesetters and 600-dpi laseredge of the image.printers use screening technologies other thanPrinter resolution The number of ink dots perhalftoning.If you are printing an image on ainch (dpi) produced by all laser printers, includingnonhalftone printer, consult your service provider orimagesetters.Most desktop laser printers have ayour printer documentation for the recommendedresolution of 600 dpi and imagesetters have aimage resolutions.resolution of 1200 dpi or higher.To determine theappropriate resolution for your image whenprinting to any laser printer, but especially toimagesetters, see screen frequency. Ink jet printers produce a spray of ink, not actualA Bdots; however, most ink jet printers have anapproximate resolution of 300 to 600 dpi andproduce good results when printing images upto 150 ppi.Screen frequency The number of printer dots orC Dhalftone cells per inch used to print grayscaleA.65 lpi: Coarse screen typically used to print newslettersimages or color separations.Also known as screenand grocery coupons.B.85 lpi: Average screen typically usedruling or line screen, screen frequency is measuredto print newspapers.C.133 lpi: High-quality screen typicallyused to print four-color magazines.D.177 lpi: Very finein lines per inch (lpi) or lines of cells per inch inscreen typically used for annual reports and images ina halftone screen.art books.The relationship between image resolution andFile size The digital size of an image, measured inscreen frequency determines the quality of detailkilobytes (K), megabytes (MB), or gigabytes (GB).in the printed image.To produce a halftone imageFile size is proportional to the pixel dimensions ofof the highest quality, you generally use an imagethe image.Images with more pixels may produceresolution that is from 1.5 to at most 2 times themore detail at a given printed size, but they requirescreen frequency.But with some images andmore disk space to store and may be slower to editand print.For instance, a 1-by-1-inch, 200-ppiimage contains four times as many pixels as a ADOBE PHOTOSHOP 6.0 95User Guide1-by-1-inch, 100-ppi image and so has four times Keep in mind that bitmap and vector data canthe file size.Image resolution thus becomes a produce different results when you resize ancompromise between image quality (capturing all image.Bitmap data is resolution-dependent;the data you need) and file size.therefore, changing the pixel dimensions of abitmap image can cause a loss in image quality andAnother factor that affects file size is file formatsharpness.In contrast, vector data is resolution-due to varying compression methods used by GIF,independent; you can resize it without losing itsJPEG, and PNG file formats, file sizes can varycrisp edges.considerably for the same pixel dimensions.Similarly, color bit-depth and the number of layersDisplaying image size informationand channels in an image affect file size.You can display information about the currentPhotoshop supports a maximum file size of 2 GBimage size using the information box at theand maximum pixel dimensions of 30,000 bybottom of the application window (Windows)30,000 pixels per image.This restriction placesor the document window (Mac OS).(Seelimits on the print size and resolution available to Displaying file and image information onan image.page 78.)To display the current image size:Changing image size andDo one of the following:resolution" (Photoshop) Press Alt (Windows) or OptionOnce you have scanned or imported an image,(Mac OS), position the pointer over the fileyou may want to adjust its size.In Photoshop,information box, and hold down the mousethe Image Size command lets you adjust the pixelbutton.The box displays the width and height ofdimensions, print dimensions, and resolution ofthe image (both in pixels and in the unit ofan image; in ImageReady, you can only adjust themeasurement currently selected for the rulers),pixel dimensions of an image.the number of channels, and the image resolution.For assistance with resizing and resampling" (ImageReady) Click an image information box,images in Photoshop, choose Help > Resizeand select Image Dimensions from the pop-upImage.This interactive wizard helps you scale yourmenu.The box displays the width and height ofimages for print or online media.the image in pixels. CHAPTER 296Getting Images into Photoshop and ImageReadyAbout resampling Choosing an interpolation methodResampling refers to changing the pixel dimen- When an image is resampled, an interpolationsions (and therefore display size) of an image.method is used to assign color values to any newWhen you downsample (or decrease the number of pixels it creates, based on the color values ofpixels), information is deleted from the image.existing pixels in the image.The more sophisti-When you resample up (or increase the number of cated the method, the more quality and detailpixels), new pixels are added based on color values from the original image are preserved.of existing pixels.You specify an interpolationThe General Preferences dialog box lets youmethod to determine how pixels are added orspecify a default interpolation method to usedeleted
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