Bit or 16bit Color Depth

> As of the CS2 version, Photoshop also includes a 32-bit mode for use with HDR images. This mode is, however, limited in its scope (see section 9.4, page 364).

JPEG saves images in 8-bit (3 x 8) format.

> Printers (or, more accurately, printer drivers) that can effectively process 16-bit image data are starting to become available.

For RGB color images 3 x 16 = 48 bits per pixel, for CMYK images its 4 x 16 bits = 64 bits per pixel.

Photoshop works with various color depths (or bit depths). The two most commonly used are:

8-bpc mode uses 8 bits (1 Byte) to represent each color component of an image. This means that in standard RGB mode, each pixel is stored using 3 x 8 (= 24) bits per channel. Many DSLRs shoot 12- or 14-bit image data per pixel and deliver 16-bit or 48-bit (3 x 16) (per pixel) results either in 16-bit TIFF or 16-bit RAW format.*

If the images delivered by digital cameras were perfect, we would never need more than 8-bit color depth, especially considering that most output devices (printers, for example) cannot handle data with more than 8-bit color depth. However, images that require no correction at all are very rare, and each correction step that involves color, contrast, saturation, or scaling produces rounding errors that reduce the effective color depth of the image. This means that if you start out with 8-bit color depth, your results will often have 6-bit color depth or less. Color smears or jagged histogram curves are the most obvious signs of this type of image quality loss. If you process 16-bit image data, you will have enough data in reserve to produce high-quality images, even after complex processing. Use 16-bit mode for as long as your memory, disk capacity, and processor power allow.

It doesn't help to convert images that are already saved with 8-bit color depth to 16-bit for processing. Image detail that is no longer (or was never) present cannot be retrieved or recreated, however much color depth you use.

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