Adobe Photoshop CS3 for Photographers phần 2 ppsx

Martin Evening Adobe Photoshop CS3 for Photographers 46 Determining output image size Image size is determined by the fi nal output requirements and at the beginning of a digital job, the most important information you need to know is: • How large will the picture appear on the page, poster, etc.? • What is the screen frequency being used by the printer – how many lpi? • What is the preferred halftone factor used to determine the output resolution? • Will the designer need to allow for page bleed, or want to crop your image? But we always use 300 ppi! There is a common misconception in the design industry that everything must be supplied at 300 pixels per inch. This crops up all the time when you are contacting clients to ask what resolution you should supply your image fi les at. Somehow the idea has got around the industry that everything from a picture in a newspaper to a 48-sheet poster must be reproduced from a 300 ppi fi le. It does not always hurt to supply your fi les at a higher resolution than is necessary, but it can get quite ridiculous when you are asked to supply a 370 MB fi le in order to produce a 30” x 36” print! with which to generate the black plate. The spacing of the pixels in relation to the spacing of the 45 degree rotated black plate is thereby more synchronized. For this reason, you will fi nd that the image output resolution asked for by printers is usually at least 1.41 times the halftone screen frequency used, i.e. multiples of ×1.41, ×1.5 or ×2. This multiplication is also known as the ‘halftone factor’, but which is best? Ask the printer what they prefer you to supply and some will say that the 1.41:1 or 1.5:1 multiplication produces crisper detail than the higher ratio of 2:1. There are other factors which they may have to take into account such as the screening method used. It is claimed that Stochastic or FM screening permits a more fl exible choice of ratios ranging from 1:1 to 2:1. Ideally this information needs to be known before the image is scanned (or captured digitally). Because if you calculate that only 10 MB worth of RGB data will actually be required, there may be no point in capturing more image data than is absolutely necessary. If the printer’s specifi cation is not available to you, then the only alternative is to scan or shoot at the highest practical resolution and resample the image later. The downside of this is that large image fi les consume extra disk space and take longer to process on the computer. If a print job does not require the images to be larger than 10 MB, then you’ll want to know this in advance rather than waste time and space working on unnecessarily large fi les. On the other hand, designers like to have the freedom to take a supplied image and scale it in the design layout program to suit their requirements. So it may seem contrary for me to state that I normally supply my fi les using a ×2 halftone factor, because that way I know there will always be enough data in the supplied fi le to allow for a 20% scaling without adversely compromising the fi nal print quality. chapter_02.indd 46chapter_02.indd 46 5/2/07 2:11:02 PM5/2/07 2:11:02 PM 47 Photoshop fundamentals Chapter 2 Pixel Aspect Ratio The Pixel Aspect Ratio is there to aid multimedia designers who work in stretched screen formats. So, if a ‘non-square’ pixel setting is selected, Photoshop will create a scaled document which will preview how a normal ‘square’ pixel Photoshop document will actually display on a stretched wide screen. And the title bar will add [scaled] to the end of the fi le name to remind you that you are working in this special preview mode. When you create a non-square pixel document the scaled preview can be switched on or off by selecting the Pixel Aspect Correction item in the View menu. Figure 2.17 The New document and New Document Preset dialogs. Creating a new document If you want to create a new document in Photoshop with a blank canvas, go to the File menu and choose New This will open the dialog shown in Figure 2.17, where you can select a preset setting from the Preset pop-up menu or manually enter new document dimensions and resolution in the fi elds below. When you choose a preset setting, the resolution will adjust automatically depending on whether it is a preset used for print or computer screen type work. You can change the default resolution settings for print and screen in the Units & Rulers Photoshop preferences dialog. The Advanced section lets you do extra things like choose a specifi c profi led color space. After you have entered custom settings in the New Document dialog these can be saved by clicking on the Save Preset button. In the New Document Preset dialog shown below you will notice that the options will allow you to select which attributes will be included in the saved preset. chapter_02.indd 47chapter_02.indd 47 5/2/07 2:11:02 PM5/2/07 2:11:02 PM Martin Evening Adobe Photoshop CS3 for Photographers 48 Altering the image size The image size dimensions and resolution can be adjusted using the Image Size dialog. The dialog will normally open with the Resample Image box checked. This means that as you enter new pixel dimension values, measurement values or adjust the resolution, the overall image size will adjust accordingly. As you adjust one set of units you will see the others adjust simultaneously. When Resample Image is unchecked, the pixel dimensions will be grayed out and any adjustment made to the image will not alter the total pixel dimensions, only the relationship between the measurement units and the resolution. Remember the rule I mentioned earlier: the number of pixels = physical dimension × (ppi) resolution. You can put that rule to the test here and use the Image Size dialog as a training tool to better understand the relationship between the number of pixels, the dimensions and the resolution. The Constrain Proportions checkbox links the horizontal and vertical dimensions, so that any adjustment is automatically scaled to both axis. Only uncheck this box if you wish to squash or stretch the image while adjusting the image size. Figure 2.18 To change the image output dimensions but retain the resolution, leave the Resample box checked. To change the image output dimensions with a corresponding change in resolution, leave the Resample box unchecked. Click on the Auto button to open the Auto Resolution dialog. This will help you pick the ideal pixel resolution for repro work based on the line screen resolution. Resolution and viewing distance In theory the larger a picture is printed, the further away it is meant to be viewed and the pixel resolution should not have to alter in order to achieve the same perception of sharpness. There are limits though, below which the quality will never be sharp enough at normal viewing distance (except at the smallest of print sizes). It also depends on the image subject matter – a picture containing a lot of mechanical detail will need more pixels to do the subject justice and be reproduced successfully. If you had a picture of a softly lit cloudy landscape, you could quite easily get away with enlarging a small image through interpolation, beyond the normal constraints. chapter_02.indd 48chapter_02.indd 48 5/2/07 2:11:06 PM5/2/07 2:11:06 PM 49 Photoshop fundamentals Chapter 2 When to interpolate? I consider ‘ interpolating up’ an image in Photoshop to be preferable to the interpolation methods found in basic scanner software. Digital fi les captured from a scanning back or multishot digital camera are extremely clean and, because there is no grain present, it is usually possible to magnify a digitally captured image much more than you would magnify a scanned image of equivalent size. There are other third-party programs that claim to offer improved interpolation, but there appears to be little evidence that you will actually gain any major improvements in image quality over and above what you can achieve using Photoshop. Image interpolation Image resampling is also known as interpolation and Photoshop can use one of fi ve methods when assigning approximated values for any new pixels that are generated. The interpolation options are located next to the Resample Image checkbox. Nearest Neighbor is the simplest interpolation method, yet I use this quite a lot, such as when I want to enlarge a screen grab of a dialog box for this book by 200% and I don’t want the sharp edges of the dialog boxes to appear fuzzy. Bilinear interpolation will calculate new pixels by reading the horizontal and vertical neighboring pixels. It is fast, and perhaps that was an important consideration in the early days of Photoshop, but I don’t see there is much reason to use it now. Bicubic interpolation provides better image quality when resampling continuous tone images. Photoshop will read the values of neighboring pixels vertically, horizontally and diagonally, to calculate a weighted approximation of each new pixel value. Photoshop intelligently guesses the new pixel values, by referencing the surrounding pixels. Figure 2.19 If Image Size is proving too confusing, the Resize Image Assistant is on hand to help guide you. This wizard is located in the Help menu and can be used to resize images both for print and for the Web. chapter_02.indd 49chapter_02.indd 49 5/2/07 2:11:08 PM5/2/07 2:11:08 PM Martin Evening Adobe Photoshop CS3 for Photographers 50 Bicubic interpolation methods The Photoshop bicubic interpolations are improved and more accurate than before, especially with regard to the downsampling of images. And if you need to apply an extreme image resize either up or down in size, I suggest that you consider using the Bicubic Sharper or Bicubic Smoother interpolation methods. Bicubic Smoother is the ideal choice if you wish to make an image bigger. In my view it is not a good idea to use Bicubic Sharper when interpolating an image up in size, because although Bicubic Smoother will result in (as the name suggests) a smoother interpolation enlargement. it is better to use Bicubic Smoother followed by a sharpening action at the end, which should be dictated by the type of print output you wish to make. Bicubic Sharper should be used when you want to reduce the pixel resolution more accurately ; for example, if you have a high resolution digital capture of detailed machinery and want to make a duplicate copy but at a much lower pixel resolution. If you reduce the image size using Bicubic Sharper the scaled down image will retain more detail and sharpness. Step interpolation Some people might be familiar with the step interpolation technique, where you gradually increase or decrease the image size by small percentages. This is not really necessary now because you can use Bicubic Sharper or Bicubic Smoother to increase or decrease the image size in a single step. Some people argue that for really extreme image size changes they prefer to use a 10% step method. Unsharp masking should always be applied last as the fi le is being prepared for print. This is because interpolating after sharpening will enhance the image artifacts introduced by the sharpening process. Planning ahead Once an image has been scanned at a particular resolution and manipulated, there is no going back. A digital fi le prepared for advertising usage may never be used to produce anything bigger than a 35 MB CMYK separation, but you never know. It is safer to err on the side of caution and better to sample down than have to interpolate up. It also depends on the manipulation work being done. Some styles of retouching work are best done at a magnifi ed size and then reduced. Suppose you wanted to blend a small element into a detailed scene. To do such work convincingly, you need to have enough pixels to work with to be able to see what you are doing. For this reason some professional retouchers will edit a master fi le that is around 100 MB RGB or bigger even. Another advantage of working with large fi le sizes is that you can always guarantee being able to meet clients’ constantly changing demands, although the actual resolution required to illustrate a glossy magazine double-page full-bleed spread is probably only around 40–60 MB RGB or 55–80 MB CMYK. Some advertising posters may even require smaller fi les than this, because the print screen on a billboard poster is that much coarser. When you are trying to calculate the optimum resolution you cannot rely on being fully provided with the right advice from every printer. Sometimes it will be necessary to anticipate the required resolution by referring to the table in Figure 2.21. This shows some sample fi le size guides for different types of print job. chapter_02.indd 50chapter_02.indd 50 5/2/07 2:11:10 PM5/2/07 2:11:10 PM 51 Photoshop fundamentals Chapter 2 Figure 2.20 The above table shows a comparison of pixel resolution, megapixels, megabyte fi le size and output dimensions at different resolutions, both in inches and in centimeters. Figure 2.21 Here is a rough guide to the sort of fi le sizes required to reproduce either a mono or CMYK fi le for printed use. The table contains fi le size information for output at multiples of x1.5 the screen ruling and x2 the screen ruling. Inches Centimeters Inches Centimeters Pixel size Megapixels MB (RGB) MB (CMYK) 200 ppi 80 ppc 300 ppi 120 ppc 1600 x 1200 2 6 7.5 8 x 6 20 x 15 5.5 x 4 13.5 x 10 2400 x 1800 4.3 12.5 16.5 12 x 9 30 x 22.5 8 x 6 20 x 15 3000 x 2000 6 17.5 23.5 15 x 10 37.5 x 25 10 x 6.5 25 x 17 3500 x 2500 8.75 25 33.5 17.5 x 12.5 44 x 31 11.5 x 8.5 29 x 21 4000 x 2850 11.4 32.5 43.5 20 x 14 50 x 36 13.5 x 9.5 33.5 x 24 4500 x 3200 14.4 41 54.5 22.5 x 16 56 x 40 15 x 10.5 37.5 x 27 5000 x 4000 20 57 76 25 x 20 62.5 x 50 16.5 x 13.5 42 x 33.5 Output use Screen ruling x1.5 Output resolution MB Grayscale MB CMYK x2 Output resolution MB Grayscale MB CMYK A3 Newspaper single page 85 lpi 130 ppi 3 12.5 170 ppi 5.5 21.5 A3 Newspaper single page 120 lpi 180 ppi 6 24 240 ppi 10.5 42.5 A4 Magazine mono single page 120 lpi 180 ppi 3 na 240 ppi 5.3 na A4 Magazine mono double page 120 lpi 180 ppi 6 na 240 ppi 10.6 na A4 Magazine single page 133 lpi 200 ppi 3.7 14.8 266 ppi 6.5 26.1 A4 Magazine double page 133 lpi 200 ppi 8 29.6 266 ppi 13 52.2 A4 Magazine single page 150 lpi 225 ppi 4.7 18.7 300 ppi 8.3 33.2 A4 Magazine double page 150 lpi 225 ppi 9.4 37.4 300 ppi 17 66.4 chapter_02.indd 51chapter_02.indd 51 5/2/07 2:11:11 PM5/2/07 2:11:11 PM Martin Evening Adobe Photoshop CS3 for Photographers 52 Converting raw data into pixels A large number of readers will probably be using a digital camera to capture their photographs and will fi nd themselves presented with a choice between capturing in JPEG or raw mode. Whichever way you look at it, all images are captured as raw data and the raw information has to be converted at some stage into an RGB pixel image that Photoshop can work with. All digital cameras have an on-board processor that will interpret the raw capture data and render it as a pixel image. This process will usually take into account the camera white balance settings, along with any other custom settings that dictate things like sharpness, levels clipping, color mode and noise reduction, etc. If you shoot using the camera’s JPEG mode, you will be letting the camera decide on-the-fl y how the conversion is to be carried out and the capture fi le output will be a fully-rendered pixel image saved using the JPEG format. If your camera output is a JPEG or a TIFF image, there is not much else you need to know about raw data right now and you can get straight down to the business of editing your images in Photoshop. When you edit a pixel image, your starting point will always be a fi xed pixel original. There are a number of ways in Photoshop that you can edit such a picture non- destructively, by using layers and adjustment layers or Smart Objects even. But your options will always be constrained by the nature of the original pixel image. Plus, adding more layers can greatly increase the overall fi le size. But if you choose to shoot in raw mode, the possibilities are endless. The raw data is just that: it is the raw image data that was captured by the sensor and the only thing that is fi xed in the raw fi le is the ISO setting that was used to capture the photograph. The raw image is therefore like a digital negative just waiting to be developed and you can have complete control over how the image is processed, whereas if you shoot using the JPEG mode, you will be letting the camera make all the raw process editing decisions for you. chapter_02.indd 52chapter_02.indd 52 5/2/07 2:11:13 PM5/2/07 2:11:13 PM 53 Photoshop fundamentals Chapter 2 Before there was Camera Raw Deferred pixel processing isn’t such a new concept. Some of you may remember the Live Picture program, which used proxy images to apply the image edits and stored these as instructions which could later be used to render a fi nal output image. The Adobe Camera Raw plug-in has evolved over several versions of Photoshop now and provides a lot of powerful features with which to process raw image fi les from selected cameras and convert them into pixel images that Photoshop can work with. The Camera Raw plug-in provides true non-destructive image editing because the raw fi le is never modifi ed. The edits you make via the Camera Raw plug-in are effectively instruction edits that are saved as metadata to a central database and can also be saved locally to XMP sidecar fi les (or in the case of DNG and other non-proprietary fi les saved to the fi le itself). This marks a radical shift in direction from the pixel-based image editing that Photoshop built its reputation on, and in Chapter 5 you can read all about all the new features in the Camera Raw 4 plug-in. If I want to preserve all the information from one of my Canon EOS 1Ds Mk II camera captures as a 16-bit TIFF fi le, the fi le would end up being almost 100 MB in size (and that is before adding extra layers). A raw master fi le by comparison will be no bigger than 15 MB (less if converted to DNG) and every time I edit the raw fi le, the edit instructions can be stored in just a few kilobytes of extra data. Raw image processing is now just as important as pixel imaging (some would argue it is even more so) and it is not just in the realm of Photoshop. There are now many other programs that will allow you to edit almost exclusively with raw images. The new Adobe Photoshop Lightroom program will let you edit and manage both raw and non-raw images. Capture One is another raw image processor that is popular with photographers and Apple’s Aperture which, like Lightroom, is primarily a workfl ow tool for digital photographers. How do we describe this raw image processing? Do we call it raw editing, instruction set editing, metadata editing? Whatever it is called, Raw offers photographers a greater level of control over how they process their images and encourages us to keep our images in their raw state longer, before it is necessary to render them as pixel images to be worked on in Photoshop. chapter_02.indd 53chapter_02.indd 53 5/2/07 2:11:14 PM5/2/07 2:11:14 PM Martin Evening Adobe Photoshop CS3 for Photographers 54 Figure 2.22 Where tools are marked with a triangle in the bottom right corner, if you mouse down on the tool you will see all the other tools that are nested in that particular group. Photoshop CS3 Tools palette The Tools palette layout contains 60 separate tools. Double-clicking any tool will automatically display the Tool options palette (if it happens to be hidden) and from there you can select individual options for that tool (see page 58). Many of the tools listed in the Tools palette have a triangle in the bottom right corner of the tool icon, which indicates that there are extra tools nested in a tool group. If you mouse down on the tool icon, this will reveal the list of tools (see Figure 2.22) and you can click on any of the tools in the list to make it the new default tool for that group. You will notice that each tool or set of tools will have an associated keyboard shortcut. This is displayed whenever you mouse down to reveal the nested tools or hover with the cursor to reveal the tool tip info; you can use these to quickly select a tool without having to always use the Tools palette to select the tool you wish to use. For example, pressing c on the keyboard will activate the crop tool and pressing j will select whichever of the healing brush group of tools is currently selected in the Tools palette. Where more than one tool shares the same keyboard shortcut, you can cycle through these other tools by holding down the S key as you press the keyboard shortcut. But if you prefer to restore the old behavior whereby repeated pressing of the key would cycle the tool selection, go to the Photoshop menu, select Preferences ➯ General and deselect the Use Shift Key for Tool Switch option (personally, I prefer using the shift key method). You can also O A-click the tool icon in the Tools palette to cycle through the grouped tools. There are specifi c situations when Photoshop will not allow you to use certain tools and displays a prohibit sign ( ). For example, you might be editing an image in 32-bit mode where only some tools can be used to edit the image. Clicking once in the image document window will call up a dialog explaining the exact reason why you cannot access or use a particular tool. Adobe On-line Any late-breaking information plus access to on-line help and professional tips are all easily accessible within Photoshop. If you click on the PS icon in the Tools palette, this will open the Adobe On-line dialog (which is also available in the Help menu). chapter_02.indd 54chapter_02.indd 54 5/2/07 2:11:14 PM5/2/07 2:11:14 PM 55 Photoshop fundamentals Chapter 2 Figure 2.23 The Tools palette with keyboard shortcuts shown in brackets. Note that the count tool is only available in the extended version of Photoshop CS3. Move tool (V) Quick selection/Magic wand (W) Brush tool/Pencil/Color replacement tool (B) Eyedropper/Color sampler/Measure/Count* (I) Zoom tool (Z) Spot Healing brush/Healing brush/Patch tool/Red eye tool (J) Eraser/Background/Magic Eraser (E) Clone Stamp/Pattern Stamp (S) Hand tool (H) Lasso tools (L) Marquee selection tools (M) Background color Exchange colors (X) Foreground color Default colors setting (D) Standard display/Quickmask display mode (Q) Screen display modes (F) History/Art History brush (Y) Blur/Sharpen/Smudge (R) Adobe On-line Pen path tools (P) Crop tool (C) Type tools/Type mask tools (T) Dodge/Burn/Sponge (O) Gradients/Paint Bucket (G) Slice/Slice select tool (K) Annotation tools (N) Path Selection/Direct Selection (A) Shape tools (U) chapter_02.indd 55chapter_02.indd 55 5/2/07 2:11:15 PM5/2/07 2:11:15 PM [...]... button button Figure 2. 26 The Tool Presets palette Figure 2. 27 The Tool Presets options 57 chapter_ 02. indd 57 5 /2/ 07 2: 11:19 PM Martin Evening Adobe Photoshop CS3 for Photographers Rectangular marquee tool Elliptical marquee tool Single row marquee tool Single column marquee tool Quick selection tool Magic wand tool Lasso tool Freeform lasso tool Magnetic lasso tool Selection tools In Photoshop the usual... the palette 70 chapter_ 02. indd 70 5 /2/ 07 2: 12: 01 PM Chapter 2 Photoshop fundamentals Automating Photoshop Why spend more time than you have to performing repetitive tasks, when Photoshop is able to automate many of these processes for you? For example, the Actions palette will let you load and save Photoshop actions, which are basically recordable Photoshop scripts In Figure 2. 45 you can see a screen... the rectangular marquee I deleted the selected areas and placed the cut-out image as a layer above a seascape image (see Figure 2. 44 for an example of how Photoshop layers work) 59 chapter_ 02. indd 59 5 /2/ 07 2: 11 :23 PM Martin Evening Adobe Photoshop CS3 for Photographers Figure 2. 30 These composite screenshots show Quick Mask views of selections created by dragging out from the center with S held down... 15 I will explain in more detail how to automate Photoshop using Actions, batch processes and droplets Figure 2. 45 The Actions palette Figure 2. 46 With Photoshop droplets you can apply a batch action operation by simply dragging and dropping a file or folder onto a droplet 71 chapter_ 02. indd 71 5 /2/ 07 2: 12: 05 PM Martin Evening Adobe Photoshop CS3 for Photographers Nudging layers and selections The keyboard... 76–77) 75 chapter_ 02. indd 75 5 /2/ 07 2: 12: 12 PM Martin Evening Adobe Photoshop CS3 for Photographers Figure 2. 52 The History Options are accessed via the History palette fly-out menu These will allow you to decide the snapshot settings I usually prefer to check the Allow Non-Linear History option, because this enables me to use the History feature to its full potential (see page 80) Figure 2. 53 This picture... chapter_ 02. indd 74 5 /2/ 07 2: 12: 09 PM Chapter 2 Photoshop fundamentals History The History feature was introduced in Photoshop 5.0 and back then it was considered a real breakthrough feature, because for the first time Photoshop offered multiple undos during a single Photoshop editing session History can play a really important role in the way you use Photoshop I thought here would be a good opportunity for. .. during a typical Photoshop session The opened image was 63 MB in size and 1300 MB of memory was allocated to Photoshop The scratch disk overhead is always quite big at the beginning of each Photoshop session, but notice how there is little proportional increase in scratch disk size with each added history state 77 chapter_ 02. indd 77 5 /2/ 07 2: 12: 16 PM Martin Evening Adobe Photoshop CS3 for Photographers. .. down, which will result in an intersected selection being made 61 chapter_ 02. indd 61 5 /2/ 07 2: 11 :29 PM Martin Evening Adobe Photoshop CS3 for Photographers Brush tool Pencil tool Blur tool Sharpen tool Smudge tool Burn tool Dodge tool Sponge tool Brush size limits The standard brush presets in Photoshop range from a single pixel to a 25 00 pixel-wide brush, with varying degrees of softness Painting tools... that is available on the DVD 58 chapter_ 02. indd 58 5 /2/ 07 2: 11 :20 PM Chapter 2 Photoshop fundamentals Figure 2. 28 A selection can be used to define a specific area of an image that you wish to work on In this example, I made an elliptical marquee selection of the inner tire wheel and followed this with an image adjustment to desaturate the red color Figure 2. 29 In this example I used the rectangle marquee... deselected, you can hold down C L to temporarily switch the move tool to the Auto Select Layer mode 73 chapter_ 02. indd 73 5 /2/ 07 2: 12: 07 PM Martin Evening Adobe Photoshop CS3 for Photographers Hand tool Zoom tool Eyedropper Color sampler Measure tool Count tool Notes tool Audio annotation tool Figure 2. 49 The Info palette showing an eyedropper color reading, a measurement readout plus two color sampler readouts . image (see Figure 2. 44 for an example of how Photoshop layers work). chapter_ 02. indd 59chapter_ 02. indd 59 5 /2/ 07 2: 11 :23 PM5 /2/ 07 2: 11 :23 PM Martin Evening Adobe Photoshop CS3 for Photographers 60 . tools (U) chapter_ 02. indd 55chapter_ 02. indd 55 5 /2/ 07 2: 11:15 PM5 /2/ 07 2: 11:15 PM Martin Evening Adobe Photoshop CS3 for Photographers 56 Figure 2. 24 The Options palette. Figure 2. 25 Here is a view. images to be worked on in Photoshop. chapter_ 02. indd 53chapter_ 02. indd 53 5 /2/ 07 2: 11:14 PM5 /2/ 07 2: 11:14 PM Martin Evening Adobe Photoshop CS3 for Photographers 54 Figure 2. 22 Where tools are marked