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Digital Cameras There are hundreds of digital still cameras on the market today, with new models being introduced daily. These cameras can be divided in 2 main groups, SLR (single lens reflex) and non-SLR (point and shoot). SLR digital cameras are very similar to 35mm SLR cameras with the film transport mechanism being replaced with a digital chip and electronic processors. Through the use of mirrors and prisms you view through the same lens used to create the picture. SLR cameras are generally pieces of entire imaging systems which include interchangeable lenses, electronic flashes, and various other specialized products. Most SLRs offer fully automatic to fully manual control of both focusing and exposure. They are more expensive and bulkier than non-SLRs, but their adaptability to almost any photographic situation makes them indispensable to professionals. Examples of digital SLR cameras are the Canon EOS Digital Rebel XT, the Nikon D200, and the Olympus E-330. Non-SLR digital cameras are generally smaller and cheaper, offering convenience at the expense of adaptability. They have permanent lenses which often offer zoom and macro focusing capabilities that are usually adequate in most situations. Focusing and exposure are usually handled automatically which again is satisfactory in most situations. Examples of non-SLR digital cameras are the Canon Powershot series, Nikon Coolpix series, and the Panasonic Lumix series. The more advanced (aka expensive) cameras in each of these series pack many professional features in a small, easy to carry body. When choosing a camera, the first decision therefore is SLR vs. non-SLR. In the SLRs favor are its’ interchangeable lenses, fully auto to fully manual operation, and its’ long term adaptability to almost any situation. The disadvantages are their size and expense. Point and shoot cameras are smaller, lighter, and cheaper. Their lack of interchangeable lenses and inability to deal with non-standard lighting conditions are definite disadvantages though for high quality scientific imaging. Camera Resolution The number of image forming pixels in a digital cameras sensor determines its resolution. Manufacturers list a cameras resolution in terms of Megapixels (millions of pixels). To produce publication quality images, I would recommend purchasing a camera with a minimum of 6 Megapixels (Mp), preferably 8-12 Mp. A 6 Mp camera will produce an uncropped image that is 6.6 x 10 inches at 300 pixels per inch (ppi). Since publishers want submitted images to be actual size at a minimum of 300ppi, you can see that a 6 Mp camera will not produce a file large enough to be used for the cover of NPJ. Most modern SLR and advanced non-SLR cameras are in the 8-12 Mp range. These cameras will produce files that are large enough, even when cropped, to be used for everything from a full bleed cover to a quarter page illustration within an article. Most cameras give you the option of making images using all the pixels or some fraction thereof if you don’t need such a large file. If you know positively that an image will only be used on a web page or in a Powerpoint presentation, you can choose one of these lower resolutions and have the ability to store more images on the memory card. Changing the cameras resolution is usually done through its menu system, so check your manual. I would recommend that for scientific work you always leave the cameras resolution at its highest setting. This will result in larger files but memory is cheap these days so just pick up a few more cards or download more often. At some future date you may decide to make a large print or you may need to crop the image and still have a decent size file for publication. If the original image is too low in resolution you won’t be able to do these things. Storage Formats and Compression When a picture is made with a digital camera, it can be stored on a memory card in several different formats and compressions. SLR type digital cameras offer more options for storage than non-SLR cameras, another point in their favor. The most common formats are JPEG, TIFF, and RAW. Choosing which file format you want to use is usually done through a cameras menu system, so check the manual for instructions. JPEG (Joint Photographic Experts Group, .jpg) is a lossy compressed file format for images. It is extremely versatile as it can greatly reduce the size of a graphics file, thus allowing it to be used on the web or sent attached to an e-mail. Most digital cameras allow you to choose from 3 JPEG compression settings: High (highest quality and largest file size), Medium (medium quality and medium file size), and Low (lowest quality and smallest file size). The greater the compression, the smaller the file size, but at a price. When compressed, information about color and tonality are discarded permanently. A compressed file may exhibit blotchiness around objects with fine detail and color banding instead of smooth gradations of tone. If you save your digital images as JPEGs, I would recommend always using the highest quality setting. Most SLR and non-SLR cameras can also save images as TIFFs (Tagged Image File Format, .tif). TIFFs are uncompressed files and are therefore very large. They can easily be up to 10 times larger than a JPEG of the exact same scene. The advantage of using the TIFF format is that all the fine detail and smooth tonal gradations of the digital image are recorded. If you are taking images that are important and specifically being made to go into print, a TIFF file will provide better quality than a JPEG file. All new digital SLRs and many non-SLRs can also save images as RAW files. Each manufacturer has its own proprietary RAW format and you will need software from the manufacturer or Adobe Photoshop CS to open them. RAW files are just what they sound like, unfiltered, unprocessed, raw data that strikes a cameras digital sensor. When you save an image as a JPEG or TIFF file the cameras processor interprets the raw data and makes all sorts of decisions about color saturation, sharpening, contrast, etc. All these decisions are recorded in the file and will affect the look of the image. A RAW file does not do this, it only records the actual sensor data and allows you to make all these decisions for yourself when you open the file on a computer. Others advantages of the RAW format are that the files are usually smaller than uncompressed Tiffs and they can be opened on the computer as 16-bit files. A 16-bit file has greater latitude for image manipulation (tonality, contrast, color balance, color saturation, etc.) after the exposure than an 8-bit file. My recommended work flow for taking scientific images of the highest quality is this: 1. Take pictures with camera set to RAW mode. 2. Download the RAW files to computer and save these as archive files that you can always return to. 3. Open the RAW file in the camera manufacturers proprietary software or any of the Adobe Photoshop CS versions (1-3 at present). Open the image as a 16 bit file. Make exposure, color, saturation, contrast, and sharpening manipulations. Save 16 bit file as an uncompressed TIFF file. 4. For publication, open the 16 bit file and resize to desired dimensions and resolution, convert to an 8 bit file and save in TIFF format. 5. For attaching to an e-mail or adding to a web site, open 16 bit file, resize accordingly, convert to 8 bit file, and save as a JPEG. If your digital camera does not offer a RAW format then use this workflow: 1. Take pictures with camera set to TIFF mode. If these files are too large for convenient storage set camera to record at the highest quality JPEG mode. 2. Download the files to computer and save these as archive files that you can always return to. 3. Open file in image manipulation software (Adobe Photoshop, iPhoto, etc.). Make exposure, color, saturation, contrast, and sharpening changes. Save as an uncompressed TIFF file. 4. For e-mail size images, change image size to 5x7’ @ 200ppi and save as JPEG with medium compression. .
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