Art 100

Introduction to Digital Photography

Digital Processing I: The Basics

Making Basic Adjustments in PhotoShop

Adobe's PhotoShop is a tremendously rich artistic tool that includes features you can use to create images wildly beyond your imagination. As an example, compare this color photograph of an aerial drop at a recent hillside fire with this painterly image of the same scene made with one of PhotoShop's "Filter" tools. In the latter, the photograph itself has merely provided the basic material from which a radically different kind of image has been created. In between the two examples is a very wide range of images that can only leave us wondering exactly what a photograph is. If I use PhotoShop to remove an offending power line, for instance, is my image still a "photograph"? The issue surfaces in a multitude of ways. A "nature photographer" was accused of abusing his medium, recently, because he produced a cute image with a whole row of ground squirrels looking over a log. Unfortunately, the original image only included one ground squirrel! He had "PhotoShopped" the others in from different photos.

In this section, we will ignore the more exotic tools available in PhotoShop and simply work on processing a photograph the way you would in a darkroom, trying to produce the best print possible. In the following section, we will open up some of the other tools available in PhotoShop but mainly with the idea of solving some of the problems that typically arise in photography. By and large, I will leave the radical departures from photographic images to your imagination and independent exploration. [I am assuming that you have either PhotoShop 7.0 or CS available.]

When you first open PhotoShop, it displays a large desktop where you can load images. On the left side is a Tool Bar and across the top (horizontally) is a Main Menu Bar. In this section, we will use only the tools available from the Main Menu Bar.

Both the 7.0 version and the CS version of PhotoShop have a "browse" utility in the File menu [though the CS browse utility is far superior]. Open Browse and find your folder for working files. You can click on one of the thumbnails to select it and you will see a larger thumbnail in the lower left. You can open the selected file by double-clicking on it. If the image needs to be rotated, you can use the Image menu and select "Rotate Canvas" choosing whichever direction is appropriate. [If a small amount of rotation is necessary to "level" the image, it is easiest to do that while cropping.] You may also wish to enlarge the image to fill the screen by using "Fit on Screen" in the View menu. The basic things you will want to do with PhotoShop at this point are to crop to the subject, size the image, adjust the light levels, adjust the hue and saturation (possibly), and sharpen the image.

Cropping There are several cropping tools in the toolbar on the left side of your screen. Click in the box and hold to see those available. The most useful tool looks like two right angles crossed and gives you a variable box superimposed on the image. You can click this tool and draw the sides of a rectangle around the part of the image you wish to keep. When you let go of the rectangle, it will darken the outside portions of the image that will be cropped out. Placing the cursor near the little boxes on the edges or corners will show you how you can change this cropping rectangle. At the edges, you can move the rectangle in or out, up or down. At the corners, you can expand or contract the rectangle or you can rotate the whole thing. [Major rotations of the image should be done with the "Rotate Image" selection in the Image menu.] When you are ready, use the Image menu and select "Crop" to finish. [Note that you can always reverse an action by going to the Edit menu and selecting "Undo xxx".]

PhotoShop has some built-in cropping tools that will crop an image to a specific size --- e.g., the classic print sizes of 4X6, 5X7, or 8X10. When you push or pull the cropping tool to include or exclude something, the rectangle will adjust the other axis appropriately so as to remain at the correct proportions. This is convenient if you want to mass-produce images of the same sizes. It may be entirely counter-productive, however, if you are trying to pursue artistic objectives. Much of what we will discuss in critique sessions deals with cropping and, in particular, how the cropping of an image calls attention to a subject and develops our interest in it. Cropping the vertical dimension down may be effective if you want to stress the horizontal idea inherent in an image. Cropping an action image so that the subject appears at the side and moves into open space may help to capture the tension of action. It is important a spend a while with the cropping tool.

Sizing the Image Use the Image menu to access the "Image Size" dialog box. You should begin with the "resample image" option unchecked; resampling will either discard pixels or create new pixels. The "Constrain Proportions" box will uncheck as a default; unless you want to create a distorted image of some kind, you should keep this unchecked. So long as resampling is unchecked, you will retain all of your pixels, merely grouping them more closely or more sparsely. The pixel dimension of your file appears at the top of the dialog box. You can begin by changing the "resolution" to 200 ppi. Note that the pixel dimension does not change but the width and height do change in proportion. Generally speaking, 200 ppi is the minimum resolution for printing photo-quality prints. Exactly what size you get will depend on the output of your camera's CCD and how much of your image you have thrown away in the cropping process. (If your camera has a relatively small megapixel output, you should do most of your cropping in camera work and leave a minimum to do in PhotoShop.) At 200 ppi a 5X7 print requires 1.4 megapixels; an 8X10 print requires 3.2 megapixels. If setting the resolution at 200 ppi gives you a larger image size than the paper you plan to use, just adjust the width or height to the correct paper size and print at higher resolution --- certainly no problem there.

The problems arise when you want to print something much larger and you don't have the pixels to pull it off! This is where resampling comes in. Suppose that you want to print a 20X30 inch poster. If you use only the pixels in your original image, the print will be "pixelated" --- that is, so large and few of them along an inch of length that you'll actually see them. [Remember that a Nikon D100 has 3000 pixels along the width which means that your image will be only 15 inches wide at 200 ppi. At 30 inches wide, you will have 100 ppi and, since they will fill the space, they will be twice as large.] To solve this problem, you check "resample image" and adjust the width to 30 inches while keeping the resolution at 200 ppi. Amazing! You have a huge image and the pixel dimension has jumped enormously. How did it do that? The answer is that PhotoShop went through your image pixel-by-pixel and created new pixels of its own between all of your originals, judging how best to fill the space. Rather than making the pixels bigger, it kept them at the appropriate size and just added more. You might notice at this point that there is an option box for resampling where you can select the algorithym that PhotoShop uses in creating pixels. It defaults on "bicubic". [Incidentally, you can improve the results of resampling by doing it in small steps --- say, 110% at a time --- even though you might have to repeat the process a number of times in order to get to the right size.]

Adjusting Levels Use the Image menu and select "Adjustments" and then "Levels" to adjust the light levels. (Select the manual option "Levels" rather than the "AutoLevels" options. In the next essay we will talk about the "Curves" option.) The display shows you a histogram of the pixel count at each brightness level from black (left) to white (right). Click on the left-most (black level) arrow and drag it over to set it under the first substantially numerous black pixels in your image. Then, click on the right-most (white level) arrow and drag it over to set it under the last substantially numerous white pixels in your image. This operation is essentially equivalent to what you would have done in the darkroom when you selected the contrast performance of your paper (or filter for your variable-contrast paper). You are filling the total light output with your image as opposed to having your image represent merely a part of the total light being output to the computer screen or printer. Notice, at the top of this dialog box, that you can survey the pixel count for the whole RGB spectrum or for each color channel separately.

The middle arrow can now be dragged to the left or right in order to change the overall midtone contrast of the image. The darkroom analog of this procedure is that of selecting an appropriate exposure time (by doing test strips) for the midtone contrasts you want. Click OK when finished.

Hue and Saturation The light levels (brightness) are merely one aspect of a color image. You may judge that the amount of color or the particular color balance (hue) need to be changed. Use the Image menu again, but select "Adjustments" and "Hue/Saturation" this time. This dialog box offers you options that you might have achieved with a film camera by selecting a particular film. Some transparency films, for inastance, are "saturated" or "highly saturated" meaning that they record higher color values in proportion to total brightness. Digital cameras often reproduce colors with less "saturation" so you may want to use the slider for saturation to adjust it upward. Note, at this point, that the dialog box provides an option at the top to select which color channel you wish to adjust. If you accept the default, you will increase the color saturation for everything. However, it may be that the sky is alreay very blue and what you really want is to emphasize the green in foreground plants. This option allows you to change saturation in some color channels of the image while leaving others about the same. Another common problem is that the blue sky may make objects on the ground tinged with blue color. Snow is a common example. If you desaturate on the blue channel, you can set the color of the snow back to a purer white. [This operation can produce digital artifacts so use it cautiously. Always check the preview image carefully.]

Sharpening At this point, you have a cropped, sized, and light-adjusted image. Before you print the image, however, you may want to sharpen it. [Remember that digital cameras have an inherent blurring (softening) effect.] Use the Filter menu and select "Sharpen" and "Unsharp Mask" to create a print that is photo sharp. The Unsharp Mask tool (in spite of its strange name) gives you the greatest amount of control in doing this. There are three variables that require attention and there is a preview screen above. If you click in the screen and drag in some direction, you can explore the effects of sharpening in different parts of the image. Start with "threshold" = 1, "radius" = 0.3 pixels, and adjust "amount" either by typing in a number or sliding the button. As you slide the button, you can watch to effect in the preview window. If you set the preview window on an edge in your image, you can see it sharpen. If you've set the radius at a fraction of a pixel (as above), you can afford to set the amount quite high (300-400%). Excessive sharpening can lead to substantial digital artifacts so you need to watch the image carefully. An overly sharpened image usually has visible halos along edges in the image. This technique requires some experimentation.

Basic Epson Printing

We are using the Epson Photo 900 InkJet printer; it is attached to a Dell PC. You should have the files you wish to print on the network, Zip disk, or CD. While you will open the files in PhotoShop in order to print them, you should have all of your "digital processing" done at this point.

Login on the PC attached to the printer and access your files. Open a file in PhotoShop. Printing requires both "Page Setup" and "Print" in the File menu. In the Page Setup box, you may need to select the Epson 900 printer, but you will need to select the paper size you are using and the correct format (portrait or landscape) for your image. You may wish to experiment with other controls and you may need to check "borderless" or "maximum" if you are trying to print your image as large as possible on the paper you are using.

In the Print box, you may need to select the Epson 900 printer again. Select printing in color or in black only. You must then tell the printer what kind of paper you are using. This is extremely important since the printer will change the amounts of ink sprayed on the paper as well as the pattern of spray in order to accommodate the paper's tendency to soak up ink or not. If you are using Epson photo paper, the type of paper is probably selectable in the printer menu and the adjustment will be made automatically. If you are using non-Epson paper, it should include directions for appropriate printing adjustments. Otherwise, you will have to experiment until you achieve satisfactory results.

The major choices remaining deal with color control. You can either allow the printer software to control color management or you can exercise custom control. This usually includes the speed of printing. Generally speaking, the selection of a slower speed will result in a finer print; however, you should take note of the fact that the only speed that is variable is the cartridge speed across the sheet. The paper itself is driven through the printer at a constant speed.

InkJet prints need to dry for about 24 hours so handle them with care. But drying is not the only thing that happens. Since the jets spray a pattern of dots for each pixel, these must "cure" by flowing into each other and mixing. [Take note how some areas of a print change over time as this process occurs.] Once dry, InkJet prints will last longer if you store them in plastic sleaves or in some other container where not exposed to sun or atmosphere.