In our last article we took a hard look at pixels. We learned that each pixel on your camera's imaging chip records only one color. For this reason digital cameras use mathematical algorithms to sample surrounding pixels in order to create the remaining two thirds of the color information that each pixel needs in order to display the correct color.

Now we need to get the pixels of your photograph saved in the best format for your needs. Here is where file types become very important in the digital photography workflow. We'll now look at the various file types available to you on your digital camera and help you decide which type works best for you. We'll take a look at the big three file types: jpeg, tiff and raw. Each file type as advantages and disadvantages and it's important that you know enough about these issues in order to choose the right file format for your individual type of photography.

RAW Files
The concept of a "raw" camera file is really not complicated at all. Remember that the imaging chip in your digital camera records only one color per pixel and then uses algorithms to construct the missing two-thirds of the color data. A "raw" file simply consists of the individual 12-bit numbers corresponding to the single color that each pixel captured when the shutter was released. Along with that raw data are separate areas in the file that contain full color thumbnails for the photo and the camera's metadata for that photo.

You should now be questioning whether your "raw" file actually contains a photograph as each recorded pixel contains only one color of the Red, Green and Blue that is required to generate a correctly colored pixel. The answer would be "no". A "raw" file cannot be displayed as a photo unless the algorithms that your camera uses to create jpeg and tiff files are applied to the "raw" data to create the missing information.

You now see the small drawback to shooting in "raw" which is the necessity of converting the "raw" data into a useable picture. This conversion, which is done in your camera for jpeg and tiff files, is done in your computer using the "raw" conversion software for your particular camera or in a program like Photoshop CS or Camera One from Phase One. However, this conversion process is actually the advantage of shooting in "raw".

With a "raw" file the process of applying the required algorithms is now given to your computer rather than to your camera. This means that the conversion process can take advantage of the more powerful processor in your computer as opposed to the processor in your camera. And, because your computer's more powerful processor is being used, camera manufacturers have the option of using more powerful algorithms to process your photograph than could be used in the camera. This can have the effect of giving you richer, sharper pictures. Each camera manufacturer's strategy for deploying the "raw" conversion algorithms is different but you can easily see that using your computer rather than your camera to create your photo is an advantage.

There is an even more powerful reason for shooting your photographs in the "raw" format and that is the ability to make exposure, white balance and other edits to your photo before you even create the photo. Photo editing applications such as Photoshop handle most exposure and white balance editing on jpeg, tiff and Photoshop files by actually removing data from the photo. To test this out just launch a photo in Photoshop, open the Levels panel (Image>Adjustments>Levels) where you'll see a histogram for your photo. At the bottom of the histogram are three diamond shaped sliders. Move in the left and right sliders toward the center. In most photos this action will have the effect of increasing the contrast of your photo. Click on the "OK" button, which accepts your levels changes. Then reopen the Levels panel and you'll most likely see the histogram with open vertical lines. These open vertical lines indicate missing information or data that has been removed from the photo in order to achieve the effect you saw on your monitor.

With a "raw" photo you can make these levels and other adjustments before you use the conversion algorithms. In Photoshop CS this is done when you double click on a "raw" photo. Photoshop will present you with a panel with various exposure, white balance, contrast, saturation, shadow and other adjustment options in addition to a very large thumbnail of your photo. You can play with these adjustments and Photoshop will adjust the thumbnail photo to give you a very good representation of what the final photo will look like if you accept these settings. When you click "OK" your editing adjustments are made to the algorithms that convert your "raw" data to reflect the changes you want to make in the photo. The most important thing to remember here is that your adjustments are being applied while your photo is being created. This means that no data is lost and your photo will have all the tonal characteristics that are possible with that file. Because no data is lost when you adjust a "raw" file this gives you the ability to make exposure changes to your photo that are as wide as two f-stops or more. This is the reason many commercial photographers shoot in "raw" and it is the reason many photojournalists use the "Raw + jpeg" setting on newer pro-level digital cameras.

Once your "raw" file is converted to a photograph in Photoshop CS, the raw conversion software for your camera or another application you will be able to save the photo as a Photoshop, tiff, jpeg or other common file format. Some programs like Nikon Capture have a batch conversion function that allows you to convert an entire folder of photos with one setting.

All you really need to remember about "raw" file formats is that they allow you to produce the best photos with the data that was captured at the time you clicked the shutter.

JPEG Files
The common language of digital photography today is "jpeg" (jay-peg). Jpeg stands for Joint Photographic Experts Group which is the organization that created the "jpeg" standard. And that is what "jpeg" actually is, a published standard that is used by all photo hardware devices and software applications that want to work with jpeg files. Having a published standard ensures that media files will work across the product lines of different vendors. So the photo you take with your Nikon camera will be recognized by your Adobe photo editing software, your Kodak print kiosk and any other device or software that wants to support jpeg files.

In the early days of digital media, hard drives, memory cards and random access memory were very small by today's standards. A typical hard drive in a computer manufactured around 1990 would be only 20 to 40 megabytes as opposed to today's hard drives of 40 to 80 gigabytes. One of the primary reasons jpeg exists is to provide the computer industry a standardized way of reducing photo and media file sizes so that they use less space on your hard drive and computer's Random Access Memory.

In our last article we calculated that a photo made with a two megapixel camera has 1200 x 1600 or 1,920,000 pixels. With one byte used for each color (R,G, B) on each pixel (or three bytes) that would make the size of the file from this little chip 1.92 million times 3 bytes or 5,760,000 bytes or 5.7 megabytes of information. That's a lot of information being produced by a little imaging chip. This is the reason jpeg exists, to reduce the amount of that information so it takes less space on your computer's hard drive.

The jpeg standard specifies how the file will be reduced in size. There are multiple steps to the process but the most important step from the photographer's point of view is the implementation of the Discrete Cosine Transformation (DCT). This is the point where your photograph is divided up into 8 pixel by 8 pixel blocks. Then the DCT is applied to each of these blocks in order to find data that can be eliminated from the block. This is where much of jpeg data loss happens. When you choose a high compression ratio for your jpeg files this is the step at which it is applied. Because your data loss happens by eliminating rounding errors resulting from the DCT, the data loss is permanent because the numbers lost to round cannot be recovered.

Further degradation is inflicted on your file where the edges of the 8 by 8 boxes meet each other. At higher compression ratios formerly smooth tones can become distorted at these edges because the averaging effect of one 8 by 8 box next to another averaged 8 by 8 box can result in a visibly large step.

The most important thing to remember about jpeg is that the entire jpeg specification is performed each time you save your photograph. Therefore it is possible to keep losing data from your valuable photographs time after time until you have a quite unpleasing photo. That's why if you are going to be working with one of your jpeg files in a photo editing program like Photoshop you should make sure that you save the file in some other format such as tiff or Photoshop's own format .psd. These formats are lossless formats that do not use compression and therefore will preserve your photo over time. By converting to another format you leave your original jpeg untouched and ready for use another time.

TIFF files
Tiff (Tagged Image File Format) files are full data files where each pixel contains the full numerical information for each of the three colors Red, Green and Blue. This is the reason tiff files are huge and it's the reason why you can fit so few images on your Lexar memory card. Our web survey at Lexar is showing that 67% of the survey takes are using six megapixel or larger cameras. If you do a little math and realize that each pixel requires one byte for each color or three bytes per pixel and then multiply that by six million you are looking at very large files.

The advantage to tiff is each file contains all of the information for the final photograph. Many photographers prefer working with tiff files when they are editing photographs because there is no data loss.

In the next article we'll look at a strategy for downloading and editing your files in a very fast and powerful way.

Other Articles by John Santoro:
- Understanding the Digital Photography Workflow

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