By David Saffir
Decisions made during image capture can have a significant impact on post-production costs and the quality of the finished prints. Two of the most important decisions we make during image capture are which file format and color space to use. Many cameras, particularly DSLRs, allow us to capture images either as JPEG, TIFF, or RAW files. They also allow us to choose to work in the sRGB, the Adobe 98 RGB, or a custom color space.
In terms of cost and quality, the Great Divide lies between JPEG and RAW file capture. It’s easy to understand why many photographers would naturally gravitate toward JPEGs. JPEGs are a compressed file format that reduces file size and increases rate of capture. JPEGs are fast, and in some ways more convenient in terms of storage and computing power. With modern in-camera automatic exposure and color correction, JPEGs can deliver good image quality.
But JPEGs have some important limitations. For example, in a recent article in Photo Techniques magazine, Timothy Edberg noted that the cameras he tested produced images with at least one f-stop less dynamic range in a JPEG file compared to a RAW capture. This makes sense, as an 8-bit JPEG digital capture uses lossy compression. A RAW file typically uses no compression, or lossless compression.
Additionally, an 8-bit JPEG file contains about 256 tones per color channel and a RAW file shot in 14-bit contains just over 16,000 tones. A 16-bit file RAW file has over 65,000 tones per channel. In color editing and in the final print, this can make a huge difference in the appearance of intense colors, such as open skies.
Not only that, but the default setting for JPEG capture is the sRGB color space. This color space is fine for digital images that will only be viewed on a computer display, but sRGB is not ideal for printing. The Adobe 98 RGB color space is significantly larger.
JPEGs also aren’t as versatile as RAW files. RAW files are very flexible, while JPEGs are pretty much locked in. With RAW files, it is much easier to correct color casts or make adjustments in certain colors or the overall color temperature, color balance, exposure, and contrast/levels.
Color artifacts and distortion in details will also be visible much sooner in a JPEG file than in the RAW. The distortions may show up in high-contrast transitions first, but can appear anywhere in the image.
Some photographers object to using RAW capture because it produces “big files” and slows the computer. Given the improvements in computer hardware and falling costs of memory and hard drives, it just doesn’t make sense to accept the limitations of JPEG capture for most uses.
Conclusion: JPEGs are fine if you plan to go straight from the camera to publication. You’ll probably want to use RAW if you plan to edit your images post-shoot.
You can find more details on the basics of RAW file processing in my book Mastering Digital Color published by Thomson Publishing.
Posted
07-24-2007 5:06 PM
by
BlogArchive