The amount of data digital SLRs capture is way more than photographers of 100 years ago would have dreamed of and a RAW photograph can even add to this luxury. Digital camera doesn’t expose a scene as the same way a photographic film does. Photographic film and silicon have a very different response to the same light. Photographic film response in a non-linear fashion like human visual system. Whereas the response of an image sensor be it a CMOS (Complementary Metal Oxide Semiconductor) or CCD (Charge-Coupled Device) is linear in its nature. So, even if a great photographer with a great understanding of exposure theory of photographic film goes out shooting might run into trouble of loosing valuable luminous data what many photographers are concerned about these days. The strength a RAW photograph must be understood if you are serious about photography which is specially designed and developed for professional photographers.
There are still a lot of arguments going about shooting RAW vs JPEG. A lot of photographers complain that a RAW processing is an extra layer of complexity into their digital workflow. But JEPGs are already processed, and processing a processed photograph will never yield a good quality. You might end up with banding, or posterization or artifacts. RAW is like a digital negative. Reasons of capturing RAW are quite obvious. JPEG becomes important only when the kind of shooting you do needs a fast delivery to your clients or you have a very little processing time, like photo journalists or event shooters; because RAW file must be processes and converted into JPEG or other usable file formats before it’s used.
There are many photographers who are so expert in getting a correct exposure on the fly. They have mastered this technique. When they look at a scene they can visualize the translated image. They require a very minimum editing to their images and often they find themselves comfortable with JPEG capture. But even with the highest degree of this technical expertise one cannot be sure to get a great exposure every time. If you are not shooting RAW having an extra copy of RAW with JPEG (RAW + JPEG) would be wise. Shooting only JPEG means throwing away the “negative” forever. Because you can’t go back in time and get the shot in raw. Time travel isn’t possible. Get home with maximum data that you DSLR can capture.
What is a JPEG Photograph?
JPEG is the acronym for Joint Photographic Experts Group. It’s already a compressed and processed image file, in computing and ready for printing as well. It’s a lossy compression that typically achieves 10:1 compression. JPEGs are generally popular for web usage. Algorithm written for this kind of compression is primarily intended for web usage to resolve bandwidth issues that large uncompressed files often cause. So shooting JPEG means you leave your camera Raw Converter to make all the decision like White Balance Correction, Color Space, Sharpening, Interpolation and other adjustments for you. Your camera may allow you to pre-configure some of the settings for this conversion to JPEG but that hardly makes a great difference.
What is a RAW Photograph?
RAW is a general term for a variety of proprietary file formats. Different camera manufacturers have different RAW file extensions, like Canon’s .CR2, Nikon’s .NEF and so on. As the name suggests it’s the RAW data, gathered by the imaging sensor of your camera. So basically it’s an uncompressed sensor data. For example, if it’s a 20 MP camera, means that has a sensor board of 20 million tiny grids of pixels each of them associated with a voltmeter that measures the charge of the photons that strike the sensor. A raw capture gives that original information untouched by the Raw Pre-processor or Raw Converter built into that camera so that it can be processed later in your computer with greater judgments and controls. So, basically what it does is it gathers the information of luminous light and converts it into pixel values. The camera settings that effect a RAW capture are only the Aperture, Shutter Speed and ISO. White Balance, Colorimetric Rendering, Sharpening and Noise Reduction settings have nothing to do with a raw capture; because these things can be readjusted on raw-processing.
It may vary manufacturer to manufacturer but a RAW capture can ensure you at least 12 bits or 4096 shades of tonal information per pixel. Whereas a JPEG file contains 8 bits or 256 shades of tonal information per pixel at most. Technically a stop of usable information is thrown away and most importantly you have no control on what gets discarded by the built-in Raw Converter in your camera.
Demosaicing is an algorithm that averages neighboring pixels values to reconstruct a full color image for CFA (Color Filter Array) interpolation. In this process a “decoder ring” gets embedded into the metadata (“data about data”) of a raw capture that helps raw converters figure out the color of each pixels. Then raw converter converts the gray scale raw capture into a color image by interpolation. This process is called demosaicing. It happens in your digital camera when you choose to shoot JPEG or in Adobe Camera Raw (or in other raw converters of your choice) when you choose to shoot Raw.
The Major Advantages of a Raw Capture
- White Balance: You may have set your preferred white balance settings in your camera. But technically, it has nothing to do with a raw capture. I mean it doesn’t effect a raw capture. Then a question may arise like “If a raw capture isn’t effected by the camera white balance settings then how does it appear identical on my display to what I set on my camera?” It’s the metadata that’s get embedded with the raw file; metadata tells the raw converter to set the default camera settings to the defaults on the raw converter. This is why it appears exactly what you set on a camera. But you have full control to readjust the white balance settings in a raw converter like Adobe Camera Raw.
- Colorimetric Interpretation: RGB filters stacked on the camera sensor are responsible for recording the luminance values of red, green and blue. But each of these values has a very wide range of shades (e.g 0 to 255). So this judgment becomes very different and subjective. RAW capture enables you to have that flexibility of readjustment.
- Gamma Correction: RAW capture has a very different tonal response than that of human eye. It captures linear gamma (gamma 1.0). So the gamma correction becomes very important to redistribute the tonal values to make a proper exposure.
- Detail Rendition: RAW images appear soft and a bit blurry. This is one of the reasons a lot of people don’t shoot raw. So the raw converter also allows to make some adjustments for noise reduction, sharpening and chromatic aberration (if there is any).
- Non-destructive: RAW files are non-destructive in nature. So a RAW file cannot be altered anyway. You can always revert to it’s original state.
- Fast Processing: Raw processing is the global adjustment you make to your photographs; it allows some advance local adjustment though. Unlike film you may automate your raw workflow or train your computer to batch process all the photographs that come out your camera to make them look good, then great when you are done with the housekeeping. If you use ACR or Lightroom you can synchronize image settings across multiple images or with a series of images which saves a lot of time.