Kevin Merchant Photography Articles

• White Balance Adjustment
• 16-bit Color
• Exposure Adjustment
• Highlight & Shadow Recovery
• Lens Optical Correction (chromatic aberation/optical distortion

What is RAW?

RAW is really a broadly applied term that encompasses the proprietary file format of every digital camera manufacturer. It is not a single, well defined file format such as TIFF or JPEG. Each camera manufacturer defines their own RAW format to contain proprietary data, captured by their cameras, that they do not wish their competitors to know about. Perhaps there are other reasons that are not generally known to the public.

But, it is to the camera manufacturer's advantage to allow a certain amount of the RAW file format definition to be known to software developers so that they can support the specific camera RAW format. What I have witnessed over many years, is that every time a new camera body is released, there is a lag time for software developers to support the camera body. It is up to the software developers to provide the updated support.

All of the major camera manufacturers provide their own software that can be used to process their own specific proprietary RAW format in order to convert images into a format that can be used by third party photo editing software such as Photoshop. The general problem with the software from these camera manufacturers is that they do not integrate well with other software used in the photographer's workflow. After all, the camera manufacturers do well at designing and making cameras; the software they provide for RAW editing, not so much.

One way to think of RAW

RAW is kind of a mystery when you first encounter it; I know it was for me. I think it helps to put RAW into the context of film photography. RAW files are literally unprocessed sensor data coming from the camera's digital sensor and stored in the proprietary format of the particular camera manufacturer that you are using - in my case Canon. There are people who would even make the distinction that the RAW sensor data is just that, data and not an image, yet.

Relative to film, the image contained in the RAW sensor data would exist before the film was even manufactured. How so? Well, when Kodak (or Fuji) formulated a particular film, they had to decide if the film was going to be color balanced for daylight (5500° Kelvin) or some other light source (tungsten - 2700° Kelvin, fluorescent - 5000° Kelvin). The color balance informed the decisions for the chemical formulation of the color layers contained in the film (I'm presuming color film here). Some films emphasized blues & greens, others emphasized reds & yellows, some emphasized skin tones and other such color formulations. The Kodachrome family of films tended to render colors in a neutral way, so that no one color was emphasized over others. Some Fujichrome films became very popular because they tended to render colors in a very saturated way, emphasizing blues & greens.

White balance

In the case of the sensor data contained in a RAW file, the color balance for the source light has not yet been rendered. These days digital cameras give the photographer a White Balance function to tell the camera what the light source is such as "daylight", "cloudy", "shade", "fluorescent" and so forth. Or, you can let the camera decide by using the "Auto" setting for White Balance where the camera makes an intelligent guess as to the light source (color temperature) - this is my typical approach. If you are shooting in RAW mode, the color (white) balance can be altered in any post processing tool of your choice (Adobe Lightroom, in my case). If however, you are capturing the image as a JPEG, then whatever color balance setting is selected in the camera is the color (white) balance that will be rendered in the actual JPEG image, which cannot be changed later. In the case of shooting in JPEG mode, the camera performs a set of processing steps on the sensor data before rendering the image as a JPEG file. This is one of many reasons that I choose to shoot all of my images with the RAW mode; rather than let the camera computer decide.

RAW adjustments

In RAW files, adjusting the color balance will globally affect all of the colors in the final image. This is not the end of what you can do to color in a RAW image before rendering it into a final image, rather it is the beginning.

For example, in Lightroom you have the ability to make exposure adjustments to the image – either increase or decrease the brightness of the image. I take full advantage of this ability by practicing a technique known as ETTR (expose to the right) which refers to making in-camera exposure adjustments based on the histogram display on the camera LCD. The technique involves over exposing to the point just short of pushing the right-most part of the histogram off the display where highlights are represented. This technique captures the largest amount of digital data for each pixel in the image. When processing in Lightroom, the exposure can be brought back down to the correct level, retaining more of the shadow detail, which is represented at the left end of the histogram.

Additionally, in Lightroom you can recover highlights and shadows in RAW files. This gives you the ability to retain detail that might otherwise be lost in a JPEG file. Of course, these adjustments have to be made judiciously. Otherwise, you can end up with unintended artifacts such as excess noise (in the case of shadow recovery) or edge banding (where an extreme highlight adjustment is made).

Bit depth

A very important distinction between RAW and JPEG is the issue of color depth. In both cases, color is represented with RGB (Red, Green & Blue) values. The JPEG file format can be considered a legacy format as it existed long before RAW came into existence. At the time the JPEG format was defined an 8-bit value for each of the three colors was considered to be sufficient for photo-realism (and still is, really). It provides 16,777,216 (256 x 256 x 256) possible distinct color values. Certainly, human color perception would have difficulty distinguishing a color difference of a value change of one but, when you are making color adjustments, the more data per pixel the better your resulting tonal values will be.

With RAW, there is no set bit depth for RGB color values – it depends on the sensor built into the camera. Today, there are cameras that have 12-bit and 14-bit color bit depths. This is determined by the analog-to-digital convertor that is built into the sensor. Suffice it to say that 12-bit or 14-bit data provides substantially more color information than an 8-bit JPEG file. One way to think about this is that you are “future proofing” your images in RAW when there is printing technology that has the ability to take advantage of this much information. This is not to say that there is no advantage today; there is. For example, when making adjustments to an image that contains a large area of continuous tone such as the sky, some 8-bit images will exhibit a banding artifact if an adjustment you make is too extreme. The higher bit depth RAW image provides more digital data for making tonal adjustments.

Optical correction

One final advantage of RAW that I would like to point out is the ability to make optical corrections to an image. All lenses have optical errors to one degree or another – chromatic aberration, vignette, pin cushion and barrel distortion. Lightroom has a large library of mathematical profiles for cameras and lenses, allowing you to make corrections to the optical errors introduced by the lens and camera combination. And, if there is no profile, it allows you to make manual adjustments that are visible. This can be very useful.

This is not meant to be an exhaustive explanation of RAW, but rather a few reasons to consider for using RAW in your own personal photography.