April 16 2012
Should photographers save their digital photos in RAW format or JPEG in their camera? Many photographers are unsure which digital photo format has the best image quality.
However, most digital photos end up as JPEGs for printing or web display. The real choice is where to process the RAW image data from the digital sensor. Should photographers do it in the camera as part of the picture taking process, or save the RAW image data and process it later on a computer using specialist software, such as Adobe Lightroom or DxO Optics Pro.
Saving digital photos in RAW format is not a magical recipe to give instantly better photos than saving as a JPEG photo in the camera. Many photographers claim the JPEGs from their camera look just as good as the RAW images, and in some cases better. They unintentionally are misleading themselves, and others, because they are not completely wrong. In ideal lighting conditions digital cameras produce JPEGs with little or no difference in quality to those from RAW files.
Processing Options and Adjustment Latitude
The difference is in the processing. Saving digital photos as a JPEG uses the camera’s processing software and the applies the same settings for sharpening, saturation, white balance and contrast.
While there is scope for adjusting the JPEGs later on a computer, there are limits to the extent of the adjustments. Adjusting JPEGs is undoing the processing already done in the camera and the JPEG file does not have all the original image information.
The RAW file contains all the image information, giving greater latitude for adjustments than a processed JPEG, where limits have been defined and information lost.
The difference emerges when lighting conditions are less than optimum. The RAW file contains all the image information from the sensor. Typically this is three sets of channel colour information, red, blue and green. Each channel has an intensity or luminosity level for the components of the light.
Digital image processing uses the relative levels of the red, blue, and green components of the light at each point on the sensor to produce the resultant luminosity and colour. The processed JPEG image contains the result of the processing, and none of the component information
The Light Meter is a Guide
The light meters in digital cameras are very good and usually give a good average representation of acceptable exposure settings for a scene. Their limitations start to show when lighting conditions are uneven. The digital camera does not understand the relative significance of the elements of scene. Here photographers need to make decisions on the areas to correctly expose, and the areas that consequentially are under or over exposed.
In difficult light, where the exposure is an estimate, photographers can use the RAW image data to adjust the interpretation of the three colour channels of data, not only individually for each photo, but for areas within the photo.
DxO say their RAW processing software, Optics Pro can reconstruct clipped highlights when one of the three coloured channels is not clipped. They use the “unclipped” channel as a basis for calculating the values of the two “clipped” channels.
The Original Remains Untouched
This is an important reason for processing RAW images on the computer rather than in the camera to produce JPEGs. Software such as DxO Optics Pro and Adobe Lightroom only apply the new image settings and adjustments to the JPEGs they produce. They save the details of the editing process separately, so they can be easily applied or changed at any time.
Why Use JPEGs
For good conditions there is little difference if any in the quality of in camera JPEGs compared to those processed separately. Because of the loss of information in producing JPEGs the image files are much smaller, making them easier to store or send over the net.
Saving digital photos in RAW format is not an instant guarantee of image quality, the results depend on the quality of the processing software, and the photographer’s ability to use the software. The RAW format allows greater precision in adjusting exposure, but at the price of increased storage costs and time spent processing images.
JPEG is a destination format for digital photos. Every time a digital photo is saved as a JPEG information is lost, and repeated editing and saving eventually causes noticeable loss in quality. Photographers who want to quickly print and share their digital photos straight from the camera using a RAW would get in the way of their fun.