Today’s Question: As a follow-up to your answer about color spaces, if the limiting factor is the image bit depth, why not just use a higher bit depth?
Tim’s Quick Answer: To truly leverage a higher bit depth to achieve the benefits of a larger range of colors, you would need to start with higher bit depth in the original capture. In other words, until and unless cameras offer higher bit depth at the sensor level, there’s little benefit to working in a higher bit depth.
More Detail: When optimizing photos, in many respects you are limited by the quality of the data you started with, which in the context of digital photography means the quality of the original image capture. For example, one of the reasons I strongly advocate for the use of raw capture rather than JPEG capture is to avoid the image quality degradation caused by lossy JPEG compression.
As noted in yesterday’s answer, bit depth determines how many possible color values an image can contain. For example, and 8-bit per channel image can contain almost 16.8 million colors, while a 16-bit per channel image can contain more than 281 trillion possible color values.
However, converting an 8-bit per channel image to 16-bit per channel won’t change the number of colors actually present in the image. Applying adjustments may increase the total number of colors represented, but doing so will never get you to the same point you would have been had you started with high-bit data to begin with.
Similarly, today’s cameras primarily process image data at 12-bit, 14-bit, or in a relatively small number of cases 16-bit per channel. Therefore, converting a raw capture to 32-bit per channel won’t provide any significant benefit in terms of expanding the existing data in the image. In addition, doubling the bit depth will double the base file size.
Furthermore, there isn’t much support for bit depths above 16-bit per channel in most imaging software. When 32-bit per channel is supported, such as in Photoshop, it is primarily focused on enabling the editing of high dynamic range (HDR) images, and many of the editing features are not supported above 16-bit per channel.
