Autotek autocad raster design 2010 用户手册

You can convert a 

 (page 390) or color image to a 

(page 382).

Converting an image to bitonal can help isolate features in an image, such as
the contour lines in a USGS map. After the image is converted to a bitonal
image, you can use the vectorization tools to convert the raster objects to
vectors.

You use a threshold value to determine which pixels become black and which
pixels become white. Raster Design uses 

 (page 396)

to speed up the editing commands.

NOTE When you use the Threshold option on an image, the foreground color of
the image is BYLAYER.

1 Click Image menu  ➤  Image Processing  ➤  Histogram.

 (page 316) dialog box is displayed.

2 Click the Threshold tab.

A preview of the image is displayed. If you selected more than one image,
the histogram displays a composite of the images' values. You can view
each image by clicking its name in the list.

NOTE The preview reflects the image as it was read from the disk. If you
have made any display-only adjustments to the image using the AutoCAD
IMAGEADJUST command, then those adjustments are not displayed in the
image preview. If you make adjustments to the image using the Histogram,
the adjustments made with IMAGEADJUST are no longer applied to the image;
instead the new settings are applied.

3 Drag the Threshold slider to determine which pixels are black and which

pixels are white. All of the pixels to the left of the slider are black and all
pixels to the right of the slider are white.

4 To adjust the scale in the histogram window, move the slider up and

down. Moving the slider up increases the scale such that low frequency
values are more visible and the highest frequency values are truncated
by the top of the window.

5 Click Apply to convert the image(s) to bitonal image(s).

100 | Chapter 6   Modifying Images