Sunday, April 11, 2010

JPEG Versus Raw

I'm trying to play catch up. Here is something that I wrote for ENG1010 Composition and Language this last session. If you see any mistakes, be sure to point them out to me so that I can learn and correct them for future readers. By the way, I gave up on trying to get the MLA format citations to render properly in the browser.



All photographers will eventually reach the point where they ask whether to shoot in JPEG or Raw format. There is no right or wrong answer to this question. Every photographer will need to weigh the pros and cons for both file formats before coming to their own conclusion. The JPEG versus Raw debate is one that has been around for as long as digital SLRs and will probably continue for many years to come.

The JPEG file format was designed with image distribution in mind and it follows a well defined standard. The generated files store 24 bits per pixel. That translates into a capacity for storing 16 million (2^24 or 16,777,216) colors. The files store 8 bits per color channel and this equates to only 256 (2^8) brightness levels. To put it into photography terms, every bit of information in the image gives an extra stop of dynamic range. The maximum dynamic range could of JPEGs can be described as 8 stops.

There is no single Raw file format but each of the file formats was designed for image capture. Every camera vendor has their own proprietary file format for each camera that they make and each file format has a specific bit depth. The generated files store 36, 42, or 48 bits per pixel which means that they are capable of storing 68 billion (2^36 or 68,719,476,736), 4.3 trillion (2^42 or 4,398,046,511,104) or 281 trillion (2^48 or 281,474,976,710,656) colors. The files store 12, 14 or 16 bits per color channel which provides for 4,096 (2^12), 16,384 (2^14) or 65,536 (2^16) brightness levels. The maximum dynamic range of Raw files can be described as 12, 14 or 16 stops, as much as twice the dynamic range available in JPEG files!

When a camera produces a JPEG file, it does so from the raw sensor data but only after it has performed some post-processing on the image. Typically the camera will apply the selected white balance, adjust the contrast and color saturation, apply an unsharpen mask and the selected color space (typically sRGB or Adobe 1998). The final step prior to saving it on disk is to compress the image. JPEG compression is not lossless, data will be lost. Cameras usually store a small amount of metadata in the JPEG files such as the date and time the photo was taken but not what camera settings were used. The file size of JPEGs is much smaller than the Raw file of the same image from the same camera which also means that JPEG files do not take as long to save to disk.

When a camera produces a Raw file, it does no post-processing; it simply dumps the unmodified sensor data. The camera settings, such as aperture, exposure time, and focal length, along with a JPEG version of the image will be stored with the rest of the metadata in the final Raw file. The image files may or may not be compressed. All of the compressed Raw file formats use a lossless compression scheme so no data will be lost during the compression phase. Raw files are larger than JPEGs so they take longer to write to disk.

JPEG files are usable in virtually every image viewer and image manipulation software available. They can be used straight out of camera (sometimes abbreviated as OOC or SOOC), if desired, because the camera has already performed the post-processing. JPEGs can be further post-processed; however, there are limitations. The image is a subset of its original form so color space changes may not be as accurate as they are with Raw files. Over- and under-exposed images can only be repaired to a small degree. Also, any time that a JPEG is saved with compression, it will further degrade.

Raw files are only recognized by a small subset of the available image manipulation and viewing software so the files require conversion before they can be used. It is quite common for them to require changes to white balance, exposure, brightness and contrast. Color space changes are often able to be made flawlessly due to the sheer number of available colors in the images. Severely over- or under-exposed images can be restored with great success. The only limitations in the post-processing exist in the software used for the post-processing and the imagination of the person performing the edits.

Ultimately, the decision of which file format is best will depend upon the needs and wants of the individual photographer, but the decision must be based on many factors such as how the image will be distributed, what level of post-processing will be done and the final purpose of the image. Again, there is no right or wrong answer to this question and the decision will need to be made for every photo shoot.


Works Cited

Goldstein, Jim. "RAW vs JPEG: Is Shooting RAW Format for Me?." JMG Galleries. JMG Galleries, Web. 7 Mar 2010. <http://www.jmg-galleries.com/articles/raw_vs_jpeg_is_shooting_raw_right_for_me.html>.

Reichmann, Michael. "Understanding Raw Files." Luminous Landscape. Web. 7 Mar 2010. <http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml>.

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