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Sponsored By HITACHI Microdrive Digital Media
Written by Shane Schmidt, Technical Marketing Manager,
Pexagon Technology, Inc.
Digital camera technology has improved with leaps and bounds over the past several years. The digital cameras of today allow us to capture an increasing number of high quality images by way of large capacity storage cards, larger imaging chips and outright faster cameras. With each generation new features are added and existing features refined. It’s these improvements that have spawned a new breed of digital camera bringing 8 megapixel advanced compacts and 6 megapixel digital single lens reflex (DSLR) cameras to the masses. A paradigm shift exists in the number of pictures we take and the image formats we shoot.
Improvements in on-board buffers, battery life, and faster, more accurate auto focus systems deliver benefits to digital shooters across the board. Performance enhancements have brought digital to a new height for the professional and the novice alike.
Larger on-board buffers enable continuous burst depths of over 20 RAW and 40 JPEG images at rates of up to 8 frames per second (fps). The Canon EOS 1D Mark II supports a burst depth of up to 20 RAW images at 8 fps, the Nikon D2H up to 25 RAW images at 8 fps and the Nikon D70 up to 144 JPEG compressed images at 3 fps. It’s speed like this that empowers the digital photographer to capture more high quality pictures in a shorter amount of time.
Capturing a Digital Image:
Capturing a digital image is a process of exposing the light sensitive image sensor (CCD or CMOS) to light. There are many things that happen in a digital camera before the file is written to the camera’s storage card. The output file type and size depend directly on any in-camera processing and compression applied to the file.
The exposure, which is the amount of light that reaches the sensor, is directly controlled by the camera’s aperture and shutter. The aperture controls the amount of light let into the camera. Think of this as a lens pupil. The camera’s shutter covers the image sensor and controls the length of time that light is able to reach the actual sensor.
Once the light reaches the camera’s imaging sensor, the sensor records the amount of light that hits each pixel as a voltage level. This voltage level is then converted from an analog voltage to a digital value by the camera’s analog to digital circuitry. Either 12 or 14 bits of data are recorded for each pixel depending on the camera. This is what is considered the unprocessed or RAW image data.
What happens to the photograph after it is captured is a function of the user-specified settings. In most cases digital cameras provide several different file formats for output including various qualities of JPEG, uncompressed TIFF and RAW. The output file type determines if the image is altered by the in-camera processing and if compression is applied to the image to reduce its size.
RAW Files Explained:
RAW files are raw image data captured by the image sensor before any in-camera processing has been applied. The cameras settings (i.e. color correction, white balance, sharpening, contrast, saturation, etc.) are disregarded, but are instead written in a header file. RAW files can be compared to exposed undeveloped film negatives in this respect.
Generally, RAW files are not compressed and are written to the camera’s storage card in this RAW format as 12 or 14 bit per channel files, depending on the camera. However, some camera manufacturers may use lossless or slightly lossy compression to reduce file size. Lossless compression is where the image is compressed, but no information is lost. Lossy compression is where the image is compressed and a certain amount of information is lost. There are also situations where minimal in-camera processing may be applied to the RAW image. The details are unknown outside of the specific camera manufacturers.
RAW files are valued for their latitude. Capturing the RAW image data and writing this information in an unaltered or mildly altered state provides the photographer with endless possibilities and potential. In most cases, post processing is required to create a finished image, but this post processing can be done on a computer system with more processing power and more advanced algorithms than that of the camera alone.
The Benefits of Shooting RAW:
Shooting RAW provides benefits over other formats for many different reasons. Depending on the situation, the benefits may be substantial or nominal. In many instances, hi-resolution JPEG files may be adequate for the task at hand, but it’s the latitude and potential for higher quality that makes RAW most appealing for pros and novices alike.
One of the greatest RAW benefits is latitude. RAW files allow the photographer to harness the full potential of each shot. Images are either unaltered, or minimally altered by the in-camera process and can then be processed externally using a computer and conversion software to achieve best results. The photographer ultimately has control over the image and can tailor settings to extract the best possible quality. This is most important in situations of difficult lighting. Color temperature and white balance can be adjusted as needed without quality degradation.
Externally processing images on a computer system allows the photographer to choose what he/she feels to be the best tool for the job. The original RAW file can be archived and revisited at a later date should a better utility become available. Fast computer processors and specialized software such as Phase One’s Capture One and Adobe’s Camera RAW plug-in for Photoshop make post processing RAW image files fast and easy. In most cases a conversion and processing software is provided with the camera or can be obtained from the manufacturer.
RAW files can be easily converted to any of the conversion software’s supported output formats including JPEG and TIFF. Conversion settings can be customized for specific print sizes. Maximum quality can be attained from each image. Using RAW files as a sort of exposed, undeveloped digital film negative gives the photographer the freedom to create and the ability to improve.
RAW files do not suffer from the same limitations other image file formats do. Because you are dealing with unaltered or minimally altered RAW image data, there is greater flexibility in applying corrections and adjustments without significant degradation in the output file’s quality. Files can be easily adjusted and converted from their RAW format to other file formats using either the RAW conversion software provided with your camera or with third party converters such as those from Adobe and Phase One. Quality is retained and the output customized for the specific applications when needed.
RAW files support either 12 or 14-bit per channel color bit-depth, depending on the camera. For example, a 12-bit RAW file supports up to 4096 (2^12) discreet levels of information or tones per channel and a 14-bit RAW file over 16,000 (2^14) levels per channel. An 8-bit JPEG file would support only 256 (2^8) discreet levels or tones per channel. The benefit here is a higher bit-depth, which translates into more color information in each of the three channels (red, green and blue). Raw files can also be converted and edited in 16-bit mode via software. This 16-bit mode allows for over 65,000 discreet levels of information per channel. What does this all mean you ask? Well, look at it this way. JPEG files support 256 possible color values per channel, a 12-bit RAW file over 4,000 and a 16-bit file over 16,000. The point being more information translates into better image quality.
When post processing the image, the added color information of the RAW file allows for expansion of specific parts of the color spectrum for correcting of less than perfect exposures. This can be quite helpful when trying to alter brightness levels or bringing out detail in shadows. The added color information of RAW files helps to avoid posterization or banding, such as found in 8-bit JPEG files. This banding occurs when there aren’t enough tonal values to display continuous tonality. Where you should see a smooth gradient, a rough jump in color or a band may appear. Evidence of the lack of tonality can be seen in the image’s histogram.
JPEG files are pre-processing compressed image files. The camera’s settings for color correction, white balance, sharpening, contrast, saturation, etc. are applied to the image and the image is compressed to reduce overall file size. The result is a finished, processed image file written to the camera’s storage card.
JPEG files generally do not require post processing and are much smaller in size when compared to RAW files from the same camera. JPEG files do suffer from quality loss due to the compression used. Depending on the level of compression used, the affects of the compression may or may not be noticeable. JPEG files are considered a finished product the moment the image is captured. You are for the most part locked into the settings you chose before you captured the image. Post processing is possible, but is hindered by the settings applied to the image in-camera. The cameras settings may have created an image suitable for a specific print size, but attempting to enlarge a print may result in less than desirable effects. JPEG files are already fully-cooked and too much manipulation can severally degrade the output quality.
RAW + JPEG Mode:
RAW+JPEG is a mode most commonly found in DSLRs and advanced compacts. This is a sort of best of both worlds solution designed to meet the need on both ends. This mode combines the latitude and quality of the RAW file with the pre-processed, small file size of the JPEG image format. Both image formats are captured and written to the media. For those who need the convenience of JPEG files, but want the latitude of shooting RAW, archive the RAW file and use the JPEG file for the task at hand.
Now photographers don’t have to choose which format to shoot as they can have their cake and eat it too. In many of the models which support this feature you are also able to choose the quality of the JPEG file produced. This option will consume more space than JPEG or RAW alone, so the only decision left now is how much storage to carry with you. Pack a Hitachi Microdrive and SHOOT RAW!