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To Shoot in Camera Raw or JPEG format
With the advent of digital cameras came issues of format and storage of digital images. The two most popular formats are raw and JPEG. Users new to digital cameras often wonder which format to use. When should you use camera raw format? The answer to this question should be never, but the technology isn't quite there yet. This article explains the advantages and challenges of camera raw and JPEG formats. What are the properties of camera raw?
- Camera raw images retain all the image information. Raw format is a file that records the information received by the camera in a fashion similar to the sensor in the camera. High quality raw images enable the editing of the image for technical adjustments such as color balance, sharpening, equalizing. It is for this reason that camera raw images are sometimes called digital film.
- Camera raw is not a single standard format type. Different camera manufacturers have different raw formats and even different camera models from the same manufacturer can have different raw formats. Each camera comes with software to read the camera's own raw format, but the capabilities of these software packages are quite limited. High-end image processing applications from Adobe support 150 different proprietary camera raw formats.
- Camera raw images are not in a format that can be viewed. The image displayed in your camera and the image on your monitor or being sent to your printer are not the same as the raw image. Displays and printers expect to receive an RGB-triple for every pixel (i.e. location in the image). The RGB-triple, one Red value, one Green value, and one Blue value, are read by displays such as computer monitors. Printers need a value for each ink they have available, usually Cyan, Magenta, Yellow, and Black, but the printers are happy to convert from RGB. Camera sensors, on the other hand, usually have one pixel with a Red sensor, two with a Green sensor, and one with a Blue sensor in every two by two square. Thus some conversion must be made from the camera raw format to a format that can be used by displays and printers, just like film negatives.
- Camera raw is not widely supported. Because of the huge variety of camera formats, and the fact that these formats are not viewable, many software applications and websites don't support any camera raw format. While there is more support for raw formats everyday, there is no guarantee this support will be long lasting. Suppose you only saved the image in camera raw format, and fifteen years from now, found out that the current applications no longer support your ancient camera model. Even worse, what if the software that came with your camera no longer ran on any available computer. Remember disk film? I no longer have that camera or the ability to deal with the film so some of the prints taken with a disk camera are my only record of that high school trip to Mexico.
Digital images can be converted into two different formats, depending on the camera, but the industry standard is JPEG. The best alternative to camera raw format is the JPEG format. - The JPEG format is universally usable. All digital cameras and computer software support the JPEG format. Camera manufacturers, who know the details of their camera's sensor, are in the best position to provide a conversion from the sensor format to a useable JPEG format. Indeed most cameras provide a direct conversion on the camera from the sensor information to the JPEG format.
- The JPEG format compresses files, saving memory. Not only does the camera's conversion put the image in a universally useable format, it also compresses the file thereby saving space on the memory card. Even with large cheap memory cards, JPEG compression means copying the image to a computer, using an image in an application, and uploading an image to be printed are all much faster than with camera raw.
- JPEG files store less information. Unfortunately, the information that JPEG intentionally stores less information than what is available to the many different varieties of camera sensors. This difference is due primarily to bit depth and color accuracy. It's also true that JPEG, in an effort to make small files, throws away some information. Good cameras, however, provide a high enough quality setting that makes the loss due to JPEG compression completely negligible.
- JPEG files are restricted in information available. The biggest problem with JPEG is bit depth. Basic JPEG files are restricted to 8 bits of information for red, 8 bits for green, and 8 bits for blue. Eight bits of information means a value between 0 and 255 is used to record the intensity of each color. Camera sensors, on the other hand, record 10 or 12 bits of information. In other words, they record values from 0 to 1023 or from 0 to 4095 instead of 0 to 255. Fundamentally, reducing the bit depth from 10 bits to 8 bits means throwing away information. It could be done by clipping the dark regions, clipping the light regions, or losing detail in both light and dark regions. Different choices can lead to dramatically different images. In some cases it's possible to get two very different 8-bit images from the same 10-bit image, both of which are stunning.
In a perfect world, JPEG would not have these limitations and would be used by all cameras and the words "camera raw" would never be heard. There are a few ongoing attempts to overcome the information limitations of JPEG and the isolation of camera raw formats.
- The JPEG committee created the JPEG 2000 standard, which provides the ability to handle much more information than JPEG, and also provides better compression and lossless compression.
- Adobe supports their own "Digital Negative (DNG)" specification in the hopes of having a unified format that could store the original information from any camera raw format.
- Microsoft is promoting HD Photo to capture more information than JPEG and provide better compression for the digital camera market.
So far JPEG support is about one hundred times more common than support for all three of these put together, but there is hope that some day soon we won't have to think about camera raw again. JPEG images are better because they are smaller, can be used anywhere and are likely to last forever. Camera raw images are better because they retain all of the information available at capture time. If you never tweak an image digitally, other than to crop it, you should continue to enjoy the bliss of JPEG. If you do everything you can to get the most out of your images digitally - adjusting the color balance, sharpening, equalizing, etc.- consider using the raw format. To get the best possible image and to keep a copy of your image for as long as possible, keep both camera raw format and a JPEG format image of the same photograph. -- Michael Gormish is a Research Scientist with Ricoh Innovations, an Associate Editor of the Journal of Electronic Imaging, member of the JPEG committee, and co-inventor on more than forty issued patents on image compression and processing.
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