Highest Quality Capture: Workflow Phase I - Black and White in Photoshop CS4 and Photoshop Lightroom - page 63

Yikes! A bit too far on the manipulation. Loss of digital
information and posterization

After an image is edited, it is natural to see some gaps and
spikes. It will depend on the image and the amount if the loss
of information will be discernible in the print

would cause the otherwise smooth transition in tonality from light to deeper
shades of blue to print with various blue stripes as the tones deepened.

The term “posterization” is used because the ef ect looks similar to how the
colors look in a mass-produced poster where the print process uses a limited
number of color inks. This ef ect ranges from subtle to extreme, and whether
this is discernible in the print depends on the level and location of the
posterization within an image.

Any process which “stretches” the image data and histogram has the potential
to cause posterization. Stretching can be caused by improper exposure, low
bit capture image editing techniques such as levels and curves in Photoshop,
or even by converting an 8-bit image into Grayscale. The best way to avoid
posterization is to work with high-bit i les and monitor the histogram
throughout the editing process, keeping image manipulation within quality
controlled limits. Above are histogram examples in a side by side comparison
that show results from common digital darkroom manipulation as compared
with potentially problematic edited data.

Posterization aka. stair stepping or
banding is an indication of extreme
loss of many brightness and tonal
values within an image

Cache Warning
Inside the Histogram palette, a small triangle with an exclamation point
inside appears as an indication that the histogram has not yet been accurately
rendered by the software. The histogram is created from the image cache,
which is a scaled down 8-bit version of the image i le. Photoshop uses
cached images in order to update the histogram dynamically as you make
adjustments to the image. To create a more accurate histogram, click on the
exclamation symbol and Photoshop will refresh the histogram and display a
fully rendered histogram.