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.An inch in the medium-sized image comprises four times as many pixelsas an inch in the largest image.Consequently, the medium-sized image consumesone-fourth the area of the largest image.Changing the printing resolutionWhen printing an image, a higher resolution translates to a sharper image withgreater clarity.Photoshop lets you change the resolution of a printed image inone of two ways:&' Choose Image ª' Image Size to access the controls that enable you to changethe pixel dimensions and resolution of an image.Then enter a value into theResolution option box, either in pixels per inch or pixels per centimeter.CautionA good idea (although not essential) is to turn off the Resample Image checkbox, as demonstrated in Figure 3-2.If you leave it on, Photoshop may add orsubtract pixels, as discussed in the  Resampling and Cropping section laterin this chapter.By turning it off, you instruct Photoshop to leave the pixelsintact but merely change how many of them print per inch.&' Alternatively, you can ask Photoshop to scale an image during the print cycle.66In Version 6, you hand down this edict in the new Print Options dialog box.Choose File ª' Print Options or press Ctrl+Alt+P to open the dialog box.Youcan enter specific Width and Height values or enter a percentage value intothe Scale option box.Lower values reduce the size of the printed image andthereby increase the resolution; higher values lower the resolution.(Chapter18 contains more information about scaling images as well as the other set-tings in the Print Options dialog box.)Photoshop saves the Resolution setting with the image; the scale settings in thePrint Options box affect the current print job only.Together, the two determine theprinted resolution.Photoshop divides the Resolution value in the Image Size dialogbox by the Scale percentage from the Page Options dialog box.For example, if theimage resolution is set to 72 ppi and you reduce the image to 48 percent, the finalprinted image has a resolution of 150 ppi (72 divided by 0.48).NoteAt the risk of boring some of you, I briefly remind the math haters in the audiencethat whenever you use a percentage in an equation, you first convert it to a decimal.For example, 100 percent is 1.0, 64 percent is 0.64, and 5 percent is 0.05.PhotoshopPart I &' Welcome to Photoshop 670Turn offFigure 3-2: Turn off the Resample Image check box tomaintain a constant number of pixels in an image and tochange only the printed resolution.TipTo avoid confusion, most folks rely exclusively on the Resolution value and leavethe Page Options dialog box Scale value set to 100 percent.The only exception iswhen printing tests and proofs.Because ink-jet and other consumer printers offerlower-resolution output than high-end commercial devices, you may find it helpfulto proof images larger so you can see more pixels.Raising the Scale value lets youaccomplish this without upsetting the Resolution value.Just be sure to restore thevalue to 100 percent after you make your test print.Changing the page-layout resolutionThe Scale value in the Print Options dialog box value has no effect on the sizeand resolution of an image imported into an object-oriented application, such asQuarkXPress or Illustrator.But these same applications do observe the Resolutionsetting from the Image Size dialog box.Specifying the resolution in Photoshop is a handy way to avoid resizing operationsand printing complications in your page-layout program.For example, I preset theresolution of all the images in this book so the production team had only to importthe images and print away.Chapter 3 &' Image Fundamentals71TipAlways remember: Photoshop is as good or better at adjusting pixels than anyother program with which you work.So prepare an image as completely as possiblein Photoshop before importing the image into another program.Ideally, you shouldnever have to resize, rotate, or crop an image in any other program.That tip is so important I m going to repeat it: Never resize, rotate, or crop an imagein Illustrator, FreeHand, CorelDraw, PageMaker, InDesign, or QuarkXPress.Get yourimage fully ready to go in Photoshop and then place it in the drawing or page-layoutprogram, position it on the page, and leave it alone.So what s the perfect resolution?After all this explanation of pixels and resolution, you might be thinking,  Okay, thisis all very interesting, but what s my bottom line? What Resolution value should Iuse? The answer is frustrating to some and freeing to others: Any darn resolutionyou like.It s true  there is no right answer, there is no wrong answer.The imagesin this book vary from 100 ppi for screen shots to 300 ppi for color plates.I ve seenlow-resolution art that looks great and high-resolution art that looks horrible.Aswith all things, quality counts for more than quantity.You take the pixels you redealt and make the best of them.That said, I ll share a few guidelines, but only if you promise to take them with agrain of salt:&' Most experts recommend that you set the Resolution value to somewherebetween 150 percent and 200 percent of the screen frequency of the finaloutput device.The screen frequency is the number of halftone dots per linearinch, measured in lpi (short for lines per inch).So ask your commercial printerwhat screen frequency he uses  generally 120 lpi to 150 lpi  and multiplythat times 1.5 or 2.&' Want to be more specific? For high-end photographic print work, it s hardto go wrong with a Resolution value of 267 ppi.That s 200 percent of 133 lpi,arguably the most popular screen frequency.When in doubt, most profession-als aim for 267 ppi.&' If you re printing on a home or small-office printer, the rules change slightly.Different manufacturers recommend different optimum resolutions for theirvarious models, but the average is 250 to 300 ppi.Experiment to see how lowyou can go, though  sometimes you can get by with fewer pixels than themanufacturer suggests.And don t forget that the quality of the paper youuse may be more to blame than a lack of pixels for a lousy print.&' What if you don t have enough pixels for 267 ppi? Say that you shoot a digitalsnapshot that measures 768 × 1024 pixels and you want to print it at 6 × 8inches.That works out to a relatively scant 128 ppi.Won t that look grainy?Probably.Should you add pixels with Image Size or some other command?No, that typically won t help.You have a finite number of pixels to work with,so you can print the image large and a little grainy, or sharp and small.Thechoice is yours.Part I &' Welcome to Photoshop 672&' What if you have a photograph or slide and you can scan it at any resolutionyou want? Flat-bed scanners typically offer two maximum resolutions, a trueoptical maximum and an interpolated digital enhancement.The lower of thetwo values is invariably the true optical resolution.Scan at this lower maxi-mum setting.Then use Image ª' Image Size to resample the image down to thedesired size and resolution, as explained in the  Resampling and Croppingsection near the end of this chapter.Orson Welles claimed that he relied on his inexperience when creating CitizenKane.He didn t know the rules of filmmaking, so they couldn t hamper him.When his assistants and technicians told him,  You can t do that, he ignoredthem because he didn t know any better.I feel the same about resolution.Take the pixels you have and try to make themlook the best you can.Then print the image at the size you want it to appear.Ifyou focus on the function of your image first and fret about resolution and othertechnical issues second, you ll produce better art [ Pobierz caÅ‚ość w formacie PDF ]