DStretch Tutorial Examples
One of the best resources for
learning DStretch are the Tutorials
by Daren Sefcik.
examples show different techniques for image enhancement using
DStretch. The first two examples are from Cueva San
Borjitas, a Great Mural site near Mulege, Baja California
Sur. The third is from Cueva Raton, a Great Mural site north
of San Ignacio, Baja California Sur. The fourth is
from the Carrizo Plain, California. A Chumash site on the
old Saucito Ranch, SLO-336. The fifth is from a little known Great
Mural site in the Sierra de San Juan.
The images in the examples are highly compressed jpeg's.
They are not suitable for DStretch enhancement. For those
who might want to try their own enhancements on these images I am
including the originals in low resolution, but only slightly
compressed form. Image for Example 1 (San
Borjitas 3174) Image for Example 2 (San
Borjitas 3160) Image for
3 (Cueva Raton) Image for Example 4
(Saucito Ranch) Image for Example 5
(Agua del Ganado). These images are also available
when using the applet
and can be opened using the open samples menu.
Additional help for using DStretch: DStretch Help
by Gary Hein.
demonstrates the differences between
colorspace choices and between mapped back and not mapped back.
Example 2 shows
the use of enhancement in clarifying pictograph composition by
improving contrast. I enhanced the image using the RGB
colorspace, not mapped back. Then I hue shifted the image by
140 degrees to get better contrast.
Example 3 demonstrates the use of the
custom RGB matrix. The first enhancement is LAB, mapped
back. The colors are enhanced and blacks and the wall
surface features are still visible. The second enhancement
uses the CRGB button. This supresses surface features and
makes the red colors more prominent. It helps to clarify the
original composition. The price to pay for this is the
supression of black or white pictographs. Note that the
black "rat", actually a puma, nearly disappears in the custom RGB
4 demonstrates the use of area selection. The
original image includes a green bush on the left. This
affects the enhancement. By choosing an area selection
avoiding the bush one gets a better enhancement. ImageJ has
many different area selection tools. In this case I used a
rectangle, but ellipses, polygons, and freehand drawing are also
available. By making very small area selections you can
create very different enhancements, sometimes getting interesting
Example 5 demonstrates
the use of hue masking. Agua del Ganado is a very poorly
preserved site. The rock is flaking off the walls, taking
the paint with it. I use a CRGB enhancement to bring out a
bird pictograph then I hue mask the result to isolate the hues in
the bird. This is not entirely successful since the same
hues exist outside the bird, but in a random pattern. I reduce the noise points outside of the bird by using
cleaning techniques. Finally I add
the result back into the original image.