Determining Bit Depth


Today’s Question: How do you know if you’re in 8-bit or 16-bit per channel bit depth?

Tim’s Quick Answer: Depending on the software you’re using, you may be able to determine the bit depth of an existing image or specify the bit depth used when creating a new image. You can also infer the bit depth of an image to some extent based on the file type.

More Detail: The first step in knowing what bit depth you’re currently working in for an image is to consider the type of file you’re working with. For example, a JPEG image will always be in the 8-bit per channel mode, because JPEG images don’t support bit depths higher than 8-bit per channel.

For a raw capture you can generally think of the image as being capable of 16-bits per channel, though in reality the source data is likely lower than that. Many cameras produce images with an analog-to-digital conversion of 12-bit or 14-bit per channel, with a relatively small number of cameras supporting 16-bit conversion. However, most imaging software only supports 8-bit and 16-bit per channel as the primary bit depth settings, so raw captures would typically be processed at 16-bit per channel even if you don’t have a camera that truly records 16-bit data.

Other file formats, such as TIFF and Photoshop PSD files, will vary since they support multiple bit depth settings.

The software you’re using may enable you to view the current bit depth. For example, in Photoshop you can go to the Image menu and choose Mode, then view which bit depth option is selected with a checkmark icon to the left of it on the menu.

In software such as Adobe Camera Raw, when processing a raw capture, you can specify the bit depth you want to use, which for a raw capture would generally be 16-bits per channel. Similarly, when exporting an image from Lightroom Classic you can specify a bit depth. The available options will depend on the file format being used, and how that file will be used, but the point is you can specify a bit depth for the image being exported.

Ultimately whether you’re able to easily determine the actual bit depth of an image depends on the software you’re using. Some software makes it easy to determine the bit depth, and others don’t provide that information at all. The key is to ensure that your workflow is structured such that you are making full use of the available bit depth for an image. For example, be sure to set the bit depth to 16-bit per channel when processing a raw capture in Adobe Camera Raw, and be sure the bit depth is set to 16-bits per channel on the External Editing tab of the Preferences dialog in Lightroom Classic for photos being sent to Photoshop.