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Benefits of 48-Bits Scanning
The Epson Perfection 4990 PHOTO and PRO Scanners have 48-bits scanning capability (internal and external). Some have wondered what are the benefits of 48-bits scanning. Most scanners have only the capability to acquire 24-bits scans. Some can do 30-bits, 36-bits or even 48-bits "internal" scans, but they cannot export (external) higher than 24-bits information to an image editing software i.e. Photoshop. The following is an attempt to explain the benefits of acquiring 48-bits scans.
| Adjusting your monitor. To fully appreciate the info on this page you'll need to have a properly adjusted monitor. If you cannot see a separation of tones in all 20 steps of this grayscale (to the right), your monitor is not properly adjusted for contrast and brightness. |  |
 | Understanding Bit-Depth. To understand 48-bits scanning, let's first discuss "bit depth". A standard 8-bits (2 to the 8th power) grayscale image has 256 shades of gray -- going from pure black (a "0" value) to pure white (with a value of "255"), and 254 gray values in between. If dithered properly, the eye sees this as a smooth transition between pure black and pure white, like the tonal strip below: |
| 24-bit Color. A standard 24-bit color image is made up of three 8-bits channels of red, green and blue (RGB) values. An 8-bit color image has about 16.7 million possible color values (256 x 256 x 256, or 2 to the 24th power). This means that each pixel has the possibility of having one of those 16.7 million color/tonal values. FYI: a CMYK image that has 8 bits/channel is 32 bits. |  |
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| Learn about how one loses tonal values when adjusting image file, and how scanning in 48-bits to acquire a greater number of tonal/color values to start with can protect your scan from these loses. See an example scanned from Ansel Adams' famous "The Tetons - Snake River" photograph! |  |
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