Getpixel returns 0 for any bitmap

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Hi,
sorry my braziliam english.
im trying to do a little program that create a 2d array that returns 1 if have color or 0 if no but ever return 0. can anybody help me? i used a listbox to see the returns

C#

Bitmap newBitmap = new Bitmap(img.Width, img.Height);
 
byte[,] buffer = new byte[100,100]; 
 
for(int y=0;y<img.Height;y++) 
{ 
  for(int x=0;x<img.width;x++)>
  { 
   Color c = newBitmap.GetPixel(x,y); 
   int lumi = Convert.ToByte((int)(c.R*0.3 + c.G*0.59 + c.B*0.11));
   buffer[x,y] = Convert.ToByte((lumi  > 127) ? 1 : 0);
   
   listBox1.Items.Add(lumi);
  } 
}

Posted 20-Oct-11 1:26am

difemen

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André Kraak · Answer 1 · 2011-10-20T01:42:00

Solution 1

The Bitmap[^] you are creating with

C#

Bitmap newBitmap = new Bitmap(img.Width, img.Height);

has a default black background. So all the values in your 2D array will be 0.

Before you start checking for colour you will need to place a colour picture in your bitmap.

Notes:
1 - Remove Convert.ToByte[^] from

C#

int lumi = Convert.ToByte((int)(c.R*0.3 + c.G*0.59 + c.B*0.11));

it serves no purpose.

2 - Your program will crash if either img.Width or img.Height is larger then 100.

Posted 20-Oct-11 1:42am

André Kraak

Comments

difemen 20-Oct-11 7:54am

if i remove the program cant compile. Cannot implicitly convert type 'int' to 'byte'.

BobJanova 20-Oct-11 8:47am

int lumi = (int)(c.R*0.3 + c.G*0.59 + c.B*0.11));
buffer[x,y] = (lumi > 127) ? (byte)1 : (byte)0;

This is more efficient I think, because the byte constants shouldn't cause a runtime cast. You might want to consider

int lumi = c.R*30 + c.G*59 + c.B*11;
buffer[x,y] = (lumi > 12700) ? (byte)1 : (byte)0;

to avoid the coercion to and from floating point.

difemen 20-Oct-11 9:00am

thanks a lot man. can you help me with the other problem?

difemen 20-Oct-11 7:56am

yes i put with
void Button1Click(object sender, EventArgs e)
{
OpenFileDialog openFileDia = new OpenFileDialog();
if (openFileDia.ShowDialog() == DialogResult.OK)
{
this.img = Image.FromFile(openFileDia.FileName) as Bitmap;
this.setPicBoxImage();
}
}

private void setPicBoxImage()
{
this.pictureBox1.Image = img;
if (img.Height < pictureBox1.Height && img.Width < pictureBox1.Width)
{
this.pictureBox1.SizeMode = PictureBoxSizeMode.CenterImage;

}

}