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Robert D Feinman

High Bit Scanning

 

Scanned in images can be corrected with less posterization if more than 8 bits are used per color.

Here is a scan done with 12 bits per color.

It has been color corrected and corrected for brightness using Photoshop curves.

It has then been converted back to 8 bits per color.

Doing adjustments in 16 bit mode preserves details since there are more values for the curve to snap to.

12 Bit Scan
12 Bit Scan

 

Here is the same scan done with 8 bits per color.

It has been color corrected and corrected for brightness in 8 bit mode directly.

8 Bit Scan
8 Bit Scan

 

This shows the histogram of the red channel after the adjustments of the 12 bit image.

Notice that there is a smooth curve showing that no color values have been lost.

12 bit red histogram
Red 12 Bit Histogram

 

This shows the histogram of the red channel after the adjustments of the 8 bit image.

Notice that there are many gaps in the curve showing that color values have been lost.

This means that nearby color values will be combined. This causes posterization and a loss of detail.

8 bit red histogram
Red 8 Bit Histogram

 

Finally we show an image which highlights the differences betwen the two scans.

The speckles show the pixels that are different in the two images.

The brightness of these pixels has been enhanced to make them easier to see.

Notice that many pixels have been changed in the darker parts of the image.

This reflects the gaps in the histogram that are concentrated at the dark end.

While the images appear almost the same on the web there are noticable difference on printed copies where a full range of colors can be reproduced.

Difference Scan
Scan Differences
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© 2001 Robert D Feinman