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3.10
Level Adjustment
The Level Adjustment dialog box shows the distribution of brightness
levels in your image. To adjust the histogram plot, drag the triangles,
located below the horizontal bar to the desired values. The left (black)
triangle changes the shadow levels. The right (white) triangle changes the
highlight levels. The middle (gray) triangle controls the midtone levels.
By varying the Shadow and Highlight points you can change the relative
shades and highlights of the image. The Shadow point represents the
darkest value and the Highlight point is the brightest value.
The Midtone point represents the Gamma setting for your particular screen.
On the histogram, the Shadow and Highlight scales are divided into 255
units.
Therefore, all pixels in the original that are darker than the current shadow
point are now completely black in the enhanced image. Conversely, all
pixels in the original that are brighter than the current highlight point are
now completely white in the processed image.
Setting the highlight point to 200 renders all pixels greater than or equal to
200, on the original, completely white in the processed image. Similarly
setting the Shadow point to 200 renders all points less than or equal to 200,
on the original, completely black in the enhanced image. Photographers
often refer to these effects as Òhigh-keyÓ or Òlow-keyÓ. High-key is an image
pushed to the white end, and low-key is an image pushed to the black end
of the tone curve.
Highlight control
Shadow control
Level Adjustment tab
Midtone (Gamma)
control
Scanning