Adobe PhotoShop CS5 : Acquiring Digital Images - Digital Cameras

Shooting a photo digitally produces a less accurate image than scanning a photo shot on film 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, the sensors are usually covered with a patterned color filter that has red, green, and blue areas. Although the filter attempts to capture all detail that the lens sees, it is unable to completely do so due to its design.

A CMOS sensor (left), such as this one from Nikon, is the standard imaging device on a digital camera. The Bayer filter arrangement (right) uses red, green, and blue pixels and is very common in digital cameras.

The filter used is typically the Bayer filter arrangement, which contains two green pixels, one red pixel, and one blue pixel. The Bayer filter uses more green because the human eye has an increased sensitivity to green. This filter allows the image to record the brightness of a single primary color (red, green, or blue) because digital cameras work in the RGB color space. 

Not all the properties of film can be fully imitated by the computer sensors in a digital camera, so 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 might only capture as little as one-fourth of the color detail. For example, if you had a desert scene with lots of red detail 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).

Does this mean you should shoot film only? Of course not; I shoot both. But it’s important to shoot for what you need. There are strengths and weakness of both film and digital capture (as well as several stylistic decisions). Ultimately, film captures a high-quality image that can be optically enlarged using the negative. However, digital capture can be more convenient and affordable because 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 important to shoot at a high pixel count (which can be accomplished by setting the camera to shoot in a high- or best-quality mode). You can always crop or shrink the image for output or display, but you should avoid enlarging the image if you don’t have to. When a digital image is enlarged, it can create unwanted image softness or pixelization (a visible blockiness). Capture as much pixel data as possible to minimize digital upsampling (increasing the resolution of the image).

Shooting JPEG vs. Raw

When digital cameras became commercially available, the memory cards used to store pictures were very expensive. Many 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. Small file sizes enabled consumers who lacked an understanding of digital imaging to attach photos to emails with minimum technical headaches. With these two scenarios in mind, manufacturers turned to an Internet-friendly format, JPEG (Joint Photographic Experts Group). It was a proven technology and one that was familiar to many users.

The JPEG format is extremely common because 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 blue in a photo of the sky. The file then discards repeated information and tells the computer to repeat certain color values or data to re-create the image.

The JPEG Options dialog box is available when you modify a JPEG file with Photoshop. When saving, you can adjust the Quality slider to reduce file size. It is best to leave Quality set to maximum if you will be making future edits to the image: This applies the least compression that could damage the image’s appearance.

Although 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, meaning that every time you modify it in Photoshop and resave as a JPEG, 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.

This image was captured as both a raw and a JPEG file when it was shot. The picture was taken with a Nikon D300, which can simultaneously write both files to the memory card when shooting.

So, if JPEG is inferior, 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 because you don’t need to buy as many memory cards. Certain scenarios like sports and photojournalism often rely on the speed associated with smaller files as well. Additionally, even many pros have been slow to abandon JPEGs due to fear of change. Learning how to use new technology requires time, something that most people are short of these days.

Newer digital cameras, generally the pro models, offer newer formats, typically called raw. These raw (or native) formats have 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 10, 12, or even 16 bits per channel instead of the 8 used by JPEG. The raw format also has a greater tonal range; hence, there is a better exposure for shadows and highlights. This extra information makes your work in Photoshop easier because it adds greater flexibility and control in image adjustments and color correction. You should have less work to do in Photoshop as well, because the image captured has more color information 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, which can reduce, or even eliminate, compression artifacts found in JPEG files. However, that extra data can increase the time it takes for the files to write to the memory card.

The raw file captures the unprocessed data from the camera’s image sensor. Although your camera may contain settings for sharpness, exposure, or lighting conditions, the raw file stores that setting as modifiable information and captures the original (unmodified) data that came through your camera’s sensors. This is very useful because it lets you easily adjust white balance within Photoshop. 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 at www.adobe.com/products/photoshop/cameraraw.html.

Because the raw data is unprocessed, you must essentially “develop” the image data inside 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. All the adjustments made in the Camera Raw dialog box are nondestructive, meaning the original image is preserved in pristine condition. You can “tweak” the image after shooting it, including being able to easily save those changes and apply them to similar exposures.

The Adobe Camera Raw dialog box is a versatile environment for “developing” your pictures. The image Ch03_Overhang.RAW is included on the DVD. Choose File > Open and navigate to the file . In Photoshop CS5, you can even make localized adjustments by painting an area to select it and then use sliders to modify it.

The Camera 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 updated the user interface. Be sure to watch my detailed video tutorial to learn more about this powerful developing tool. Fortunately, the Camera Raw dialog box is fairly intuitive, especially once you understand the concepts of adjusting images. 

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 on 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 in 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. Additionally, if the camera’s battery were to be depleted during image transfer, the memory card and its contents can become corrupt.

A better option for downloading images from a digital camera is to purchase a stand-alone memory card reader. There are many options available, so consider these questions and choose wisely:

• Do you need only one card format, or do you need to read multiple formats?

• Do you want a read-only device, or do you want to be able to erase and reformat cards while they are in the reader?

• How fast do you want your files to transfer? Be wary of card readers that are USB 1, which can take a long time to transfer files. Look for USB 2, USB 3, FireWire, or eSATA for faster data rates. Laptop users with a card slot can purchase an effective card adapter for fast file transfers without tying up ports.

• Do you want to transfer multiple cards at once? Some readers allow for two or even four cards to be mounted at one time so you can initiate a large transfer and walk away.