Visual Basic 6 Black Book:Working With Images
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Next, we get the red, green, and blue color values for each pixel and add the value in intAddOn to those color values, making sure they don’t go higher than 255 (of course, you can also darken images by subtracting values here, although you should make sure the resulting color values don’t go below 0):


Private Sub Command1_Click()
Dim x, y, intAddOn As Integer
Dim bytRed, bytGreen, bytBlue As Integer
…
For x = 1 To intUpperBoundX
For y = 1 To intUpperBoundY
bytRed = Pixels(x, y) And &HFF
bytGreen = ((Pixels(x, y) And &HFF00) / &H100) Mod &H100
bytBlue = ((Pixels(x, y) And &HFF0000) / &H10000) Mod &H100

bytRed = bytRed + intAddOn
If bytRed > 255 Then bytRed = 255
bytGreen = bytGreen + intAddOn
If bytGreen > 255 Then bytGreen = 255
bytBlue = bytBlue + intAddOn
If bytBlue > 255 Then bytBlue = 255

Pixels(x, y) = RGB(bytRed, bytGreen, bytBlue)
Next y
Next x
End Sub


Finally, we just copy the new pixels to the second picture box, Picture2:


Private Sub Command1_Click()
Dim x, y, intAddOn As Integer
…
For x = 1 To intUpperBoundX
For y = 1 To intUpperBoundY
Picture2.PSet (x, y), Pixels(x, y)
Next y
Next x

End Sub


The result of this code appears in Figure 19.13. Now we’re lightening images pixel by pixel in Visual Basic.


Figure 19.13  Lightening an image pixel by pixel.
The code for this example is located in the imagelighten folder on this book’s accompanying CD-ROM.

Creating “Embossed” Images
You can create a striking visual effect by embossing an image, which makes it appear to be raised in 3D. Using the technique developed in the previous few topics, we can work pixel by pixel in an image to emboss it.
Let’s see how this works in an example. Here, we’ll take the image in a picture box, Picture1, and emboss the image in it when the user clicks a button, Command1, displaying the result in a second picture box, Picture2. To be able to work pixel by pixel, set each picture box’s ScaleMode property to vbPixel (3).
We start by storing the image in Picture1 in an array named Pixels:


Const intUpperBoundX = 300
Const intUpperBoundY = 300
Dim Pixels(1 To intUpperBoundX, 1 To intUpperBoundY) As Long
Private Sub Command1_Click()
Dim x, y As Integer

For x = 1 To intUpperBoundX
For y = 1 To intUpperBoundY
Pixels(x, y) = Picture1.Point(x, y)
Next y
Next x
…


Now we’ll emboss the image in the Pixels array. Embossing is the process of plotting the difference between a pixel and a pixel above and to the left of it; this difference is added to 128 to make the whole image appear gray. Here’s one important note: when we’re setting a pixel, we use both it and the pixel to the upper-left of it, which means that to avoid incorporating pixels we’ve already set, we will proceed from the bottom-right of the array, not the upper-left. Here’s how that process looks in code:


Private Sub Command1_Click()
Dim bytRed, bytGreen, bytBlue, bytAverage As Integer
…
For x = intUpperBoundX To 2 Step –1
For y = intUpperBoundY To 2 Step –1
bytRed = ((Pixels(x – 1, y – 1) And &HFF) – (Pixels(x, y) And _
&HFF)) + 128
bytGreen = (((Pixels(x – 1, y – 1) And &HFF00) / &H100) Mod _
&H100 – ((Pixels(x, y) And &HFF00) / &H100) Mod &H100) + 128
bytBlue = (((Pixels(x – 1, y – 1) And &HFF0000) / &H1000) Mod _
&H100 – ((Pixels(x, y) And &HFF0000) / &H10000) Mod &H100)_
+ 128

bytAverage = (bytRed + bytGreen + bytBlue) / 3
Pixels(x, y) = RGB(bytAverage, bytAverage, bytAverage)
Next y
Next x

End Sub


Note that we also average all the color values together so that the resulting image is a grayscale image. When we’re done, we just copy the image to the second picture box, Picture2:


Private Sub Command1_Click()
Dim bytRed, bytGreen, bytBlue, bytAverage As Integer
…
For x = 1 To intUpperBoundX
For y = 1 To intUpperBoundY
Picture2.PSet (x – 2, y – 2), Pixels(x, y)
Next y
Next x

End Sub


Running this program gives the result you see in Figure 19.14. Now we’re embossing images in Visual Basic.


Figure 19.14  Embossing an image pixel by pixel.
The code for this example is located in the imageemboss folder on this book’s accompanying CD-ROM.

Creating “Engraved” Images
In the previous topic, we created embossed images by taking the difference between a pixel and the pixel to the upper-left of it and adding 128 to the result to create a grayscale image. We can also create engraved images by taking the difference between a pixel and the pixel to its lower-right and adding 128 to the result.
The code to create engraved images is the same as that to create embossed images, except that we work in the reverse direction and use the pixel to the lower-right, not the upper-left. Here’s the new image effect loop:


For x = 2 To intUpperBoundX – 1
For y = 2 To intUpperBoundY – 1
bytRed = ((Pixels(x + 1, y + 1) And &HFF) – (Pixels(x, y) And _
&HFF)) + 128
bytGreen = (((Pixels(x + 1, y + 1) And &HFF00) / &H100) _
Mod &H100 – ((Pixels(x, y) And &HFF00) / &H100) Mod &H100)_
+ 128
bytBlue = (((Pixels(x + 1, y + 1) And &HFF0000) / &H10000)_
Mod &H100 – ((Pixels(x, y) And &HFF0000) / &H10000) Mod_
&H100) + 128

bytAverage = (bytRed + bytGreen + bytBlue) / 3
Pixels(x, y) = RGB(bytAverage, bytAverage, bytAverage)
Next y
Next x


When you put this code to work, you see the result as in Figure 19.15. Now we’re engraving images in Visual Basic. (To be able to work pixel by pixel, make sure you set each picture box’s ScaleMode property to vbPixel (3).)

Figure 19.15  Engraving images by working pixel by pixel.
The code for this example is located in the imageengrave folder on this book’s accompanying CD-ROM.




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