How To Get Your Hands on Good Digital Images
- Digital Cameras
- Scanners
- Importing from CD/DVD
- Stock Photo Services
- Public Domain Images
This chapter is from the book
This chapter is from the book
This chapter is from the book
While Photoshop is a great tool for a lot of tasks, most of them center around the sizing, manipulation, and processing of digital images. While their contents may vary, all digital images are essentially the same: They are composed of pixels that contain color and luminance information. Photoshop’s powerful features will allow you to adjust those pixels to better match your needs.
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While the destination may be the same, the path your digital images take to get inside of Photoshop will vary. Some may start out as digital images acquired with a still camera, while others may get loaded via a scanner. You may also find yourself turning to online resources to find specialized images. Let’s take a look at the many ways to acquire your digital images.
Digital Cameras
This book will not teach you how to use your digital camera. There are many excellent books on that subject as well as classes offered. What we will address is how the pixels are converted, what file format you should choose to shoot your images, and how to transfer them to your computer.
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Digital Camera Technology
Shooting a photo digitally produces a less accurate image than scanning a photo shot on film and scanned with a flatbed scanner using a high SPI setting. This is because digital cameras capture data using photosensitive electronic sensors. These sensors record brightness levels on a per-pixel basis. However, these sensors usually are covered with a patterned color filter that has red, green, and blue areas. While the filter attempts to capture all detail that the lens sees, it is unable to due to its design.
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The filter used is usually the Bayer filter arrangement, which contains two green pixels and one red and one blue. The Bayer filter uses more green because the human eye has increased sensitivity to green. This filter allows the image to record the brightness of a single primary color (red, green, or blue) as digital cameras work in the RGB color space. The RGB values combine using the additive color theory (which we briefly discussed in Chapter 1, “Digital Imaging Fundamentals”) and form an image when viewed from a suitable distance.
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Since not all traditional camera functions can be fully imitated by the computer sensors in a digital camera, the camera must interpolate the color information of neighboring pixels. This averaging produces an anti-aliased image, which can show visible softening. When anti-aliasing is present, hard edges are blended into one another. Sometimes this can be desirable (with low-resolution Internet graphics where you reduce file size by limiting color). Other times, anti-aliasing can produce an undesirable softness when you print an image. Depending on the colors in the original image, a digital camera may only capture as little as one-fourth of the color detail. For example, if you had a scene like a desert with a great detail of red, and little green or blue, the sensor would rely on the red areas of the filter (which only cover a fourth of the sensor face).
Am I saying to shoot film only? Of course not... I shoot both. What is important is to shoot for what you need; there are strengths and weakness to both film and digital (as well as several stylistic decisions as well). Ultimately, film captures a high-quality image that can be optically enlarged using the negative. However, digital can be more convenient and affordable as you get instant feedback on the images you have just taken, and you eliminate the time-consuming process and costs associated with developing the film. It is just important to note that you should shoot at a higher pixel count (which can be accomplished by telling the camera to shoot a high- or best-quality mode). You can always crop or shrink the image down for output or display, but you should avoid having to enlarge the image as this will create unwanted softness or pixelization (a visible blockiness) in the image.
Shooting JPEG vs. RAW
When digital cameras became commercially available, the memory cards used to store pictures were very expensive. Photographers could not afford multiple or high-capacity cards, so they wanted more images to fit on a single, smaller card. Many users also emailed their pictures to friends and family. Smaller file size enabled consumers who lacked an understanding of digital imaging to attach photos to email with minimum technical headaches. With these two scenarios in place, manufacturers turned to an Internet-friendly format, JPEG. It was a proven technology and one that was familiar to many users.
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The Joint Photographic Experts Group ( JPEG) format is extremely common as most hardware and software manufacturers have built support for it into their products. The JPEG format is also extremely efficient at compressing images, and it is a good format for continuous tone images, such as photos. A JPEG file looks for areas where pixel detail is repeated, such as the color white on every key of your computer keyboard. The file can then discard repeated information and tell the computer to repeat certain color values or data to re-create the image.
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While JPEG is a good format for distributing images (due to their compatibility and small file size), it is not great for image acquisition or production. A JPEG file is lossy, as every time you modify it in Photoshop, and resave, additional compression is applied to the image. Over subsequent compressions, the image quality can noticeably deteriorate. This is similar to the act of making a photocopy of another photocopy: Additional image deterioration occurs with each processing step. The visible loss in image detail or accuracy is referred to as compression artifacts.
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So, if JPEG is so bad, why do so many people use it? Money and resistance to change are the simple answers. It’s a lot cheaper to shoot JPEG images, as you don’t need to buy as many memory cards. Additionally, even many pros have been slow to abandon JPEGs. Learning how to use new technology requires time, something that most people are short of these days.
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Newer digital cameras, generally the pro models, offer a newer format called raw. This newer format has several benefits over shooting to JPEG. The images are usually captured at a higher bit rate, which means that the pixels contain more information about the color values in the image. Most raw files have a depth of 12 bits (or 16 bits) per channel instead of the 8 used by JPEG. This raw format also has a greater tonal range, hence better exposure for shadows and highlights. This extra information will make your work in Photoshop easier as it adds greater flexibility and control in image adjustments and color correction. You should have less work to do as well, since the image captured more detail than a JPEG would have.
Raw files can be two to six times larger than JPEG files. This extra data is used to hold more image detail. This can reduce, or even eliminate, compression artifacts. However, that extra data can take longer for the files to write to the memory card.
The raw file captures the unprocessed data from the camera’s image sensor. While your camera may contain settings for sharpness, exposure, or lighting conditions, the raw file stores that info as modifiable information, and captures the original (unmodified) data that came through your camera’s sensors. Each manufacturer treats the format differently, using a proprietary format. Fortunately, Photoshop frequently updates its raw technology to support the newest cameras on the market. To find out if you can access a particular camera format from within Photoshop, visit Adobe’s Web site (www.adobe.com/products/photoshop/cameraraw.html).
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Because the raw data is unprocessed, you must essentially “develop” the image data inside of Photoshop. You’ll be presented with several choices when opening a raw image. You can choose to adjust several options related to the image, as well as the lens and lighting conditions. You can “tweak” the image after shooting it (as opposed to JPEG, which is limited to the settings you had when shooting).
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Is DNG the New Raw?
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In 2004 Adobe released the Digital Negative Specification (DNG). The code and specifications have been made publicly available so manufacturers can build in support to their products. The goal was to replace several proprietary raw file formats with a universal format. Despite initial optimism, camera manufacturers have been very slow to adopt it (some even refusing). At this point, DNG files are a useful way to archive raw files and attach additional metadata. You can find out more at Adobe’s site at www.adobe.com/products/dng/main.html.
The raw dialog box has continued to evolve since it was first introduced as a purchased add-on to Photoshop 7. Subsequent versions of Photoshop have continued to modify the user interface. To help you learn about these options, your safest bet is to read the many entries in the Adobe Help Center. Fortunately, the Camera RAW dialog box is fairly intuitive, especially once you understand the concepts of adjusting images. Once you have completed Chapter 10, “Color Correction,” you should feel much more confident using the options in the Camera RAW dialog box.
Acquiring Images from a Digital Camera
There are two major ways of downloading images from a digital camera. Which connection type you choose will depend upon your work environment and budget for additional hardware.
The first method involves plugging the camera directly into the computer. Many cameras ship with a connecting cable (generally USB). The advantage of this approach is that it doesn’t require an extra hardware purchase. The primary disadvantages of this method are that it ties up the camera and it is hard on delicate ports built into the camera. If you break the USB port by constantly plugging and unplugging a camera, it can lead to an expensive service bill. The data port is interconnected with several other systems on the camera; a break at one end can result in problems in other areas.
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A better option is to purchase a stand-alone memory card reader. There are many options available, so ask yourself a few questions and choose wisely:
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