Bit Depth Importance


Today’s Question: How important is it really to work at a high bit depth? Will I even be able to see the difference in my photos?

Tim’s Quick Answer: That depends. When a photo requires strong adjustments or will be presented as a monochrome image, working at a high bit depth can be critical. When working with a full-color photo that only requires minor adjustments, the bit depth isn’t likely to be a significant factor. I simply prefer a conservative approach that involves always using 16-bit per channel mode when optimizing photos.

More Detail: The bit depth used when applying adjustments to your images affects the total number of tonal and color values available for the image. That, in turn, determines the degree to which smooth gradations of tone and color can be maintained, even as you apply strong adjustments.

A monochrome (such as black and white) image at a bit depth of 8-bits per channel will only have 256 shades of gray available, while a 16-bit image will have 65,536 shades of gray. That can translate into a tremendous risk of posterization (the loss of smooth gradations) for an 8-bit monochromatic image, even with modest adjustments.

A color image at 8-bits per channel will have more than 16.7 million possible tonal and color values available. At 16-bits per channel that number jumps to over 281 trillion tonal and color values.

While 16.7 million possible tonal and color values is generally adequate for ensuring smooth gradations within the photo, strong adjustments can result in a degree of posterization. It will usually take a very strong adjustment (perhaps combined with an image that had been under-exposed initially) to create visible posterization with a color image, but the point is that there is a degree of risk.

For many photographers the difference may be virtually non-existetnt between an 8-bit per channel and 16-bit per channel image for a color photograph that doesn’t require strong adjustments. However, my personal preference is to always work in the 16-bit per channel mode when possible, just to ensure I am always producing an image with the highest potential quality.

It is important to note, however, that if the original capture does not provide high-bit data, there is no real advantage to converting an 8-bit image to the 16-bit per channel mode. This is one of the key reasons I prefer RAW capture rather than JPEG capture (along with the risk of compression artifacts with JPEG captures).