This article has been
excerpted from book "Graphics Programming with GDI+".
Images represented by the Image class and its inherited classes can also store
attributes. The ImageAttributes class represents the attributes of an image.
DrawImage can take a parameter of type ImageAttributes, which represents how the
colors are applied to an image shown it is rendered. The ImageAttributes class
has no properties, but it provides many useful methods. Let's take a look at the
method provided by the ImageAttributes class.
The SetWrapMode Method
Sometimes we need to fill a graphics shape with a texture that's smaller or
large than the graphics shape. The wrap mode-represented by the WrapMode
enumeration-specifies how a texture is tiled when it is larger or smaller than
the area being filled. The members of the WrapMode enumeration are described in
Table 8.7.
SetWrapMode is used to set the wrap mode of a texture or gradient. This method
takes three parameters: a wrap mode (WrapMode), a color (Color), and a clamp
(Boolean). The last two parameters are optional. If the clamp value is true, the
texture will be clamped to the image boundary; otherwise there is no clamping.
Listing 8.9 uses this method. First we create an ImageAttributes object and set
the wrap mode using SetWrapMode. Then we create an Image object using FromFile,
followed by a call to DrawImage with an argument of the ImageAttributes object.
DrawImage draws an image on the form, rendered using the colors defined by
ImageAttributes.
TABLE 8.7: WrapMode members
|
Member |
Description |
Clamp |
Clams the texture
or gradient to the object boundary. |
|
Title |
Tiles the gradient
or texture. |
|
TileFlipX |
Reverse the
texture or gradient horizontally and then tiles it. |
|
TileFlipXY |
Reverse the
texture or gradient horizontally and vertically then tiles it. |
|
TileFlipY |
Reverse the
texture or gradient vertically and then tiles it. |
LISTING 8.9: Using the SetWrapMode method of ImageAttributes
private
void SetWrapMode_Click (object
sender System.EventArgs e)
{
Graphics g = this.CreateGraphics();
g.Clear(this.BackColor);
// Create ImageAttributes object
ImageAttributes ImgAttr = new ImageAttributes();
// Set wrap mode to tile
ImgAttr.SetWrapMode(WrapMode.Tile);
// Create an image
Image curImage =
Image.FromFile("dnWatcher.gif");
// Draw image
Rectangle rect = new
Rectangle(0, 0, 400, 400);
g.DrawImage(curImage, rect, 0, 0, 400, 400,
GraphicsUnit.Pixel, ImgAttr);
// Dispose of object
g.Dispose();
}
Figure 8.8 shows the output from Listing 8.9. If the image is smaller than the
surface, images are wrapped
Note: The WrapMode enumeration is defined in the System.Drawing.Drawing2D
namespace. Don't forget to add the namespace reference to the project.
FIGURE 8.8: Wrapping images
The SetGamma Method
The SetGamma method sets the gamma value, which represents the brightness of a
graphics shape, for all graphics objects, including images, brushes, and pens.
Gamma values range from 0.1 to 5.0 (normally 0.1 to 2.2), with 0.1 being the
brightest and 5.0 the darkest.
This method takes a floating type parameter as gamma value and a second optional
parameter of the ColorAdjustType enumeration type. Using the ColorAdjustType
enumeration from the Imaging namespace, you can even specify which GDI+ objects
use this color adjustment. For example, if you want to apply gamma values on
text only, you can do so using ColorAdjustType.Text, which is described in Table
8.8. The following code snippet sets the gamma value of ImageAttributes.
ImageAttributes ImgAttr = new ImageAttributes();
imageAttr.SetGamma(2.0f, ColorAdjustType.Default);
Now you can use this ImageAttributes object as a parameter of the DrawImage
method.
The SetColorMatrix Method
A color matrix represents how colors are represented in an Image object. As we
saw in Section 8.3.2, the ColorMatrix object represents a color matrix.
TABLE 8.8: ColorAdjustType members
|
Member |
Description |
|
Any |
Reserved |
|
Bitmap |
For Bitmap Object
only |
|
Brush |
For Brush object
only |
|
Count |
The number of
types specified (used internally by GDI+) |
|
Default |
For all objects
that do no have their own color adjustment information |
|
Pen |
For Pen objects
only |
|
Text |
For text only |
SetColorMatrix applies a color matrix to an image. This method takes a parameter
of the ColorMatrix class, with two optional parameters of ColorMatrixFlag and
ColorAdjustType enumeration.
Often we don't want all graphics objects to be affected by a color adjustment.
Suppose we have some graphics shapes, an image, and some text, and we want only
the image to be affected by the color adjustment specified by the SetColorMatrix
method. The ColorAdjustType enumeration allows us to specify which graphics
objects uses the color adjustment information. Table 8.8 describes the members
of the ColorAdjustType enumeration.
ColorMatrixFlag specifies the types of images and colors that will be affected
by the color adjustment settings. The ColorMatrixFlag enumeration has three
members: AltGrays, Default, and SkipGrays. AltGrays is not available for use
except by the .NET Framework internally, so basically ColorMatrixFlag provides
the option of affecting gray colors or not. The Default value means that all
colors will be affected; SkipGrays means that gray shades will not be affected.
(You may want to skip some of the gray shades that are used when you're
smoothing images.)
In Listing 8.10 we create ColorMatrix and ImageAttributes objects. Then we call
SetColorMatrix to add a color matrix to ImageAttributes.
ImageAttributes.SetColorMatrix takes ColorMatrix as its first argument.
LISTING 8.10: Drawing semitransparent images
private
void SetColorMatrix_Click (
object sender System.EventArgs e)
{
Graphics
g = this.CreateGraphics();
g.Clear(this.BackColor);
Rectangle rect = new
Rectangle(20, 20, 200, 100);
Bitmap bitmap = new
Bitmap("MyPhoto.jpg");
// Create an array of matrix points
float[][]
ptsArray =
{
new float[] {1,
0, 0, 0, 0},
new float[] {0,
1, 0, 0, 0},
new float[] {0,
0, 1, 0, 0},
new float[] {0,
0, 0, 0.5f, 0},
new float[] {0,
0, 0, 0, 1}};
// Create a color matrix
ColorMatrix
clrMatrix = new ColorMatrix(ptsArray);
// Set ColorMatrix properties
if (clrMatrix.Matrix34 <= 0.5)
{
clrMatrix.Matrix34 = 0.8f;
clrMatrix.Matrix11 = 0.3f;
}
// Create image attributes
ImageAttributes imgAttributes = new
ImageAttributes();
// Set color matrix
imgAttributes.SetColorMatrix(clrMatrix,
ColorMatrixFlag.Default,
ColorAdjustType.Bitmap);
g.FillRectangle(Brushes.Red, rect);
rect.Y += 120;
g.FillEllipse(Brushes.Black,
rect);
// Draw image
g.DrawImage(bitmap,
new Rectangle(0,
0, bitmap.Width, bitmap.Height),
0, 0,
bitmap.Width, bitmap.Height,
GraphicsUnit.Pixel, imgAttributes);
// Dispose of object
g.Dispose();
}
Figure 8.9 shows the output from Listing 8.10. A rectangle and a circle are
drawn, and then an image with lower color resolution, as specified by
ImageAttributes.
FIGURE 8.9: Drawing semitransparent images
The SetNoOp and SetColorKey Methods
The SetNoOp method sets the NoOp correction value for Graphics objects. When
NoOp is set, no adjustments to the color will be made during the rendering
process.
SetColorKey sets the low and high color values for graphics objects and shapes.
The SetColorKey method takes a parameter of type ColorAdjustType enumeration
(see Table 8.8) that specifies the type of the graphics objects and shapes to be
affected by SetColorKey.
Listing 8.11 applies gamma effect and sets color key values using the
SetColorKey method.
LISTING 8.11: Applying SetGamma and SetColorKey
private
void SetNoOp_Click (object
sender, System.EventArgs e)
{
// Create a Graphics object
Graphics g = this.CreateGraphics();
g.Clear(this.BackColor);
// Create two colors
Color lClr =
Color.FromArgb(245, 0, 0);
Color uClr =
Color.FromArgb(255, 0, 0);
// Create ImageAttributes object
ImageAttributes ImgAttr = new ImageAttributes();
// Set color key
ImgAttr.SetColorKey(lClr, uClr,
ColorAdjustType.Default);
// Set gamma
ImgAttr.SetNoOp(ColorAdjustType.Default);
// Create an Image object
Image curImage =
Image.FromFile("dnWatcher.gif");
// Draw image
Rectangle rect = new
Rectangle(0, 0, 400, 400);
g.DrawImage(curImage, rect, 0, 0, 400, 400,
GraphicsUnit.Pixel, ImgAttr);
// Dispose of object
g.Dispose();
}
Figure 8.10 shows the output from Listing 8.11.
Now if we uncomment the following line in Listing 8.11:
//ImgAttr.SetNoOp (ColorAdjustType.Defualt);
the output will look like Figure 8.11. Using SetNoOp cancels all image attribute
effects.
The SetThreshold Method
The SetThreshold method sets the transparency range (threshold) for a specified
category. This method takes one parameter representing a threshold value ranging
between 0.0 and 1.0, and an optional second parameter of type ColorAdjustType.
The value of the threshold specifies a cutoff point for each component of color.
For example, suppose that the threshold is set to 0.8 and the value of the red
component is 240. Because the value of the red component (240) is greater than
0.8, the red component will be changed to 255 (full intensity).
imageAttr.SetThreshold(0.8f, ColorAdjustType.Default);
FIGURE 8.10: Applying SetGamma and SetColorKey
FIGURE 8.11: Using the SetNoOp method
The SetBrushRemapTable Method
We have already discussed how the SetRemapTable method sets a remap table to the
specified ColorMap object. The OldColor and NewColor properties of ColorMap
represents old and new colors, respectively. SetBrushRemapTable converts only
the colors of brushes. The ColorMap class also provides both ColorMap and
NewColor properties.
Listing 8.12 creates a ColorMap object, sets its OldColor and NewColor
properties, and then calls SetBrushRemapTable with the ColorMap object.
LISTING 8.12: Using SetBrushRemapTable
private
void SetBrushRemapTable_Click (object
sender System.EventArgs e)
{
Graphics g = this.CreateGraphics();
g.Clear(this.BackColor);
ColorMap[]
clrMapTable = new ColorMap[1];
clrMapTable[0]
= new ColorMap();
clrMapTable[0]
= OldColor = Color.Red;
clrMapTable[0]
= NewColor = Color.Green;
ImageAttributes ImgAttr = new ImageAttributes();
ImgAttr.SetBrushRemapTable(clrMapTable);
Image curImage =
Image.FromFile("Simple.bmp");
g.DrawImage(curImage, 0, 0);
Rectangle rect = new
Rectangle(0, 0, 400, 400);
g.DrawImage(curImage, rect, 0, 0, 400, 400,
GraphicsUnit.Pixel, ImgAttr);
// Dispose of object
g.Dispose();
}
The Clear Methods
The ImageAttributes class provides a "clear" method for almost every set method
we have discussed in this section. The clear methods take either no parameter or
an optional parameter of ColorAdjustType enumeration. These clear methods are
listed in Table 8.9.
TABLE 8.9: The clear methods of ImageAttributes
|
Method |
Description |
|
ClearBrushRemapTable |
Clears color remap
table for brush. |
|
ClearColorKey |
Clears color key
values for the graphics objects specified by the ColorAdjustType
enumeration. |
|
ClearColorMatrix |
Clears color
adjust matrix to all zeros. |
|
ClearGamma |
Clears gamma
effect for the graphics objects specified by the ColorAdjustType
enumeration. |
|
ClearNoOp |
Clears NoOp
setting for all graphics objects. |
|
ClearOutputChannel |
Clears output
channel selection for graphics objects specified by the ColorAdjustType
enumeration. |
|
ClearOutputChannelColorProfile |
Clears output
channel section and color profile file for graphics objects specified by
the ColorAdjustType enumeration. |
|
ClearRemapTable |
Clears color remap
table for graphics objects specified by the ColorAdjustType enumeration. |
|
ClearThreshold |
Clears threshold
values for graphics objects specified by the ColorAdjustType
enumeration. |
Suppose that we wanted to clear the color key values for all graphics objects.
We would use the ClearColorKey method as follows:
imageAttr.ClearColorKey(ColorAdjustType.Default);
Conclusion
Hope the article would have helped you in understanding
Image Attributes and the ImageAttributes Class in GDI+. Read other articles on GDI+ on the website.
|
This book teaches
.NET developers how to work with GDI+ as they develop applications
that include graphics, or that interact with monitors or printers.
It begins by explaining the difference between GDI and GDI+, and
covering the basic concepts of graphics programming in Windows. |