image manipulation windows phone - windows-phone-7

Question

I have an image in a Windows Phone app. There I have an array containing 10 values, depending on those values I am setting my contrast as
problem is when I am sliding forward it is perfect. But when reversing back image is not getting to original image.
I have already tried and researched a lot
Actually its a code belongs to code project site---
private double lastslidervalue;
private void sliderContrast_ValueChanged(object sender, MouseButtonEventArgs e)
{
if (sliderContrast == null) return;
double[] contrastArray = { 1, 1.2, 1.3, 1.6, 1.7, 1.9, 2.1, 2.4, 2.6, 2.9 };
int nIndex = (int)sliderContrast.Value-(int)this.lastslidervalue;
if (nIndex == -1)
{
int nIndex=this.lastslidervalue-sliderContrast.Value
this.lastslidervalue=sliderContrast.value
}
else
{
nIndex = (int)sliderContrast.Value-(int)this.lastslidervalue;
this.lastslidervalue=sliderContrast.value
}
double CFactor = contrastArray[nIndex];
WriteableBitmap wb;
wb = new WriteableBitmap(wbOriginal.PixelWidth, wbOriginal.PixelHeight);
//wb = new WriteableBitmap(imgOriginal);
wbOriginal.Pixels.CopyTo(wb.Pixels, 0);
int h = wb.PixelHeight;
int w = wb.PixelWidth;
for (int i = 0; i < wb.Pixels.Count(); i++)
{
int pixel = wb.Pixels[i];
int B = (int)(pixel & 0xFF); pixel >>= 8;
int G = (int)(pixel & 0xFF); pixel >>= 8;
int R = (int)(pixel & 0xFF); pixel >>= 8;
int A = (int)(pixel);
R = (int) Math.Max(0, Math.Min(255, (((R - 128) * CFactor) + 128)));
G = (int)Math.Max(0, Math.Min(255, (((G - 128) * CFactor) + 128)));
B = (int)Math.Max(0, Math.Min(255, (((B - 128) * CFactor) + 128)));
if (R > 255) R = 255; if (G > 255) G = 255; if (B > 255) B = 255;
if (R < 0) R = 0; if (G < 0) G = 0; if (B < 0) B = 0;
wb.Pixels[i] = B | (G << 8) | (R << 16) | (A << 24);
}
wb.Invalidate();
image1.Source = wb;
}
I am here using value changed event of slider....
after debugging I found that R value is continuosly decreasing after sliding forward.
ex--117,114,101,95 ,but after sliding backward R should be increased but,it is decreasing continuosly like after 95 it is 76....
Please help anybody.............

Answer 1

Your contrastArray has only positive values. When you're moving the slider back, you are always applying a positive change to your contrast, or crash your app.
double[] contrastArray = { 1, 1.2, 1.3, 1.6, 1.7, 1.9, 2.1, 2.4, 2.6, 2.9 };
This is all larger than 1.
Also, this can crash your app:
int nIndex = (int)sliderContrast.Value-(int)this.lastslidervalue;
this.lastslidervalue=sliderContrast.value
if (nIndex == -1) return;
because sometimes the change can be larger than one in the negative side. This means that you get nIndex smaller than -1 which then crashes here:
double CFactor = contrastArray[nIndex];
However, you could use this code to get what you want
private void sliderContrast_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
if (sliderContrast == null) return;
double[] contrastArray = { 0.1, 0.2, 0.3, 0.4, 0.6, 1, 1.2, 1.3, 1.6, 1.7, 1.9, 2.1, 2.4, 2.6, 2.9};
int nIndex = Convert.ToInt32(sliderContrast.Value);
double CFactor = contrastArray[nIndex];
//.... the rest is the same
And if you set the starting value for the slider to be Value = 5 (do this in XAML) and make the maximum value a bit larger (to expand for the added values), then the change to the right and to the left should get the contrast higher or lower depending on the slider value. Works on my machine. :)