I am trying to write a program that clicks on the first pixel it finds which has a certain color. Unfortunately, it appears that sometimes my program is unable to detect that there is actually the color on the screen. I am taking a screenshot of the screen and then using the GetPixel() method to find the color of every pixel.
Here is my method I use:
private static Point FindFirstColor(Color color)
{
int searchValue = color.ToArgb();
Point location = Point.Empty;
using (Bitmap bmp = GetScreenShot())
{
for (int x = 0; x < bmp.Width; x++)
{
for (int y = 0; y < bmp.Height; y++)
{
if (searchValue.Equals(bmp.GetPixel(x, y).ToArgb()))
{
location = new Point(x, y);
}
}
}
}
return location;
}
In order to take a screenshot of my screen, I use:
private static Bitmap GetScreenShot()
{
Bitmap result = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, PixelFormat.Format32bppArgb);
{
using (Graphics gfx = Graphics.FromImage(result))
{
gfx.CopyFromScreen(Screen.PrimaryScreen.Bounds.X, Screen.PrimaryScreen.Bounds.Y, 0, 0, Screen.PrimaryScreen.Bounds.Size, CopyPixelOperation.SourceCopy);
}
}
return result;
}
Even when I use a color which I know is on the screen, it still returns Point.Empty. What is the reason for this?
Just copied your method and used as color the find Color.Black and it worked without any problems.
The only thing that's currently maybe not correctly in your code is that you don't immediately return after finding the first matching point. Instead you simply continue to iterate over all points thus leading to the fact that you'll going to return the last occurrence of a matching color.
To avoid this you can change your code into:
private static Point FindFirstColor(Color color)
{
int searchValue = color.ToArgb();
using (Bitmap bmp = GetScreenShot())
{
for (int x = 0; x < bmp.Width; x++)
{
for (int y = 0; y < bmp.Height; y++)
{
if (searchValue.Equals(bmp.GetPixel(x, y).ToArgb()))
{
return new Point(x, y);
}
}
}
}
return Point.Empty;
}
Related
I have a video stream from a camera to an Image in a WPF. I am trying to access the WritableBitMap Image pixel by pixel before displaying it. As a test I am trying to set the whole image to white or black. In both cases however, I get the AccessViolationException error.
I checked other posts and it seems that this error is very wide and not specific to my case. I can't seem to know why I am not getting this working.
So what is the best way to play with the pixels in my case? or why this is not working? Any help is appreciated
private async void UpdateMasterCameraPreview(IdsFrame frame)
{
if (masterImage != null)
frame.Image.CopyTo(masterImage);
else
masterImage = frame.Image.ToWriteableBitmap();
//BitmapImage temp = ConvertWriteableBitmapToBitmapImage(masterImage);
WriteableBitmap temp = masterImage;
// Here I get the exception, on every pixel access
for (int y = 0; y < temp.PixelHeight; y++)
for (int x = 0; x < temp.PixelWidth; x++)
temp.SetPixel(x, y, 255);
masterImage = temp;
masterImage.Lock();
masterImage.AddDirtyRect(new Int32Rect(0, 0, masterImage.PixelWidth, masterImage.PixelHeight));
masterImage.Unlock();
if (OnMasterFrameCaptured != null)
OnMasterFrameCaptured(this, new CameraFrameCapturedArgs(CameraType.Master, masterImage));
}
You have swapped X and Y, i represents height, j represents width, then you shouldcall SetPixel like:
temp.SetPixel(j, i, 255);
On cases like this is better to use meaningful names for variables, like X and Y.
I ended up using the answer of this post. I now can edit raw pixel data of any WriteableBitmap image before sending it to image control in WPF. Below is what I exactly used but here I just convert every frame to some transparency under a condition:
public void ConvertImage(ref WriteableBitmap Wbmp)
{
int width = Wbmp.PixelWidth;
int height = Wbmp.PixelHeight;
int stride = Wbmp.BackBufferStride;
int bytesPerPixel = (Wbmp.Format.BitsPerPixel + 7) / 8;
unsafe
{
byte* pImgData = (byte*)Wbmp.BackBuffer;
// set alpha to transparent for any pixel with red < 0x88 and invert others
int cRowStart = 0;
int cColStart = 0;
for (int row = 0; row < height; row++)
{
cColStart = cRowStart;
for (int col = 0; col < width; col++)
{
byte* bPixel = pImgData + cColStart;
UInt32* iPixel = (UInt32*)bPixel;
if (bPixel[2 /* bgRa */] < 0x44)
{
// set to 50% transparent
bPixel[3 /* bgrA */] = 0x7f;
}
else
{
// invert but maintain alpha
*iPixel = *iPixel ^ 0x00ffffff;
}
cColStart += bytesPerPixel;
}
cRowStart += stride;
}
}
}
And the routine of using it is like this:
masterImage.Lock();
ConvertImage(ref masterImage);
masterImage.AddDirtyRect(new Int32Rect(0, 0, masterImage.PixelWidth, masterImage.PixelHeight));
masterImage.Unlock();
I develop a screen sharing app and i would like to make it as efficient as posibble so im trying to send only the differences between the screen shots.
So, suppose we have this image for example:its a 32bpprgba image with transpert parts around.
I would like to store each one of the blocks here as a rectangle in a List and get them bounds. It may sounds very complex but actually it just requires a little logic.
This is my code so far:
private unsafe List<Rectangle> CodeImage(Bitmap bmp)
{
List<Rectangle> rec = new List<Rectangle>();
Bitmap bmpRes = new Bitmap(bmp.Width, bmp.Height);
BitmapData bmData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), System.Drawing.Imaging.ImageLockMode.ReadOnly, bmp.PixelFormat);
IntPtr scan0 = bmData.Scan0;
int stride = bmData.Stride;
int nWidth = bmp.Width;
int nHeight = bmp.Height;
int minX = int.MaxValue; ;
int minY = int.MaxValue;
int maxX = 0;
bool found = false;
for (int y = 0; y < bmp.Height; y++)
{
byte* p = (byte*)scan0.ToPointer();
p += y * stride;
for (int x = 0; x < bmp.Width; x++)
{
if (p[3] != 0) //Check if pixel is not transparent;
{
found = true;
if (x < minX)
minX = x;
if (x > maxX)
maxX = x;
if (y < minY)
minY = y;
}
else
{
if (found)
{
int height = getBlockHeight(stride, scan0, maxX, minY);
found = false;
Rectangle temp = new Rectangle(minX, minY, maxX - minX, height);
rec.Add(temp);
y += minY;
break;
}
}
p += 4;//add to the pointer 4 bytes;
}
}
return rec;
}
as you see im trying to scan the image using the height and width, and when i found a pixel i send it to GetBlockHeight function to get it's height:
public unsafe int getBlockHeight(int stride, IntPtr scan, int x, int y1)
{
int height = 0; ;
for (int y = y1; y < 1080; y++)
{
byte* p = (byte*)scan.ToPointer();
p += (y * stride) + (x * 4);
if (p[3] != 0) //Check if pixel is not transparent;
{
height++;
}
}
return height;
}
But im just not getting the result... i think there's somthing with the logic here... can anyone light my eyes? i know it requires a bit time and thinking but i would very very appreciate anyone who could help a little.
In your current algorithm, after successfully matching a rectangle, you increase y with its height and break out of the inner loop. This means you can only detect data for one rectangle per horizontal line.
If I were you I'd think about the following things, before jumping back into the code:
Save the complete image as a PNG file, and look at its size. Is further processing really required?
Are these rectangles accurate? Will there be scenario's in which you would be constantly sending the contents of the entire screen anyway?
If you're developing for Windows, you might be able to hook into the procedure that invalidates areas on the screen, in which case you wouldn't have to determine these rectangles yourself. I don't know about other OSes
Also I personally wouldn't try to solve the rectangle-detection algorithm in a "nesty" for-loop, but go with something like this:
public void FindRectangles(Bitmap bitmap, Rectangle searchArea, List<Rectangle> results)
{
// Find the first non-transparent pixel within the search area.
// Ensure that it is the pixel with the lowest y-value possible
Point p;
if (!TryFindFirstNonTransparent(bitmap, searchArea, out p))
{
// No non-transparent pixels in this area
return;
}
// Find its rectangle within the area
Rectangle r = GetRectangle(bitmap, p, searchArea);
results.Add(r);
// No need to search above the rectangle we just found
Rectangle left = new Rectangle(searchArea.Left, r.Top, r.Left - searchArea.Left, searchArea.Bottom - r.Top);
Rectangle right = new Rectangle(r.Right, r.Top, searchArea.Right - r.Right, searchArea.Bottom - r.Top);
Rectangle bottom = new Rectangle(r.Left, r.Bottom, r.Width, searchArea.Bottom - r.Bottom);
FindRectangles(bitmap, left, results);
FindRectangles(bitmap, right, results);
FindRectangles(bitmap, bottom, results);
}
public Rectangle GetRectangle(Bitmap bitmap, Point p, Rectangle searchArea)
{
int right = searchArea.Right;
for (int x = p.X; x < searchArea.Right; x++)
{
if (IsTransparent(x, p.Y))
{
right = x - 1;
break;
}
}
int bottom = searchArea.Bottom;
for (int y = p.Y; y < searchArea.Bottom; y++)
{
if (IsTransparent(p.X, y))
{
bottom = y - 1;
break;
}
}
return new Rectangle(p.X, p.Y, right - p.X, bottom - p.Y);
}
This approach, when fully implemented, should give you a list of rectangles (although it will occasionally split a rectangle in two).
(Of course instead of providing the bitmap, you'd pass the pointer to the pixel data with some metadata instead)
I'm having some trouble reading back pixel values from a Bitmap that I'm generating. I first generate a bitmap named maskBitmap in my class using this code:
void generateMaskBitmap()
{
if (inputBitmap != null)
{
Bitmap tempBitmap = new Bitmap(inputBitmap.Width, inputBitmap.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
using (Graphics g = Graphics.FromImage(tempBitmap))
{
Brush brush = Brushes.Black;
for (int y = 0; y < tempBitmap.Height; y += circleSpacing)
{
for (int x = 0; x < tempBitmap.Width; x += circleSpacing)
{
g.FillEllipse(brush, x, y, circleDiameter, circleDiameter);
}
}
g.Flush();
}
maskBitmap = (Bitmap)tempBitmap.Clone();
}
}
I then try to apply the mask to my original image using the following code:
void generateOutputBitmap()
{
if (inputBitmap != null && maskBitmap != null)
{
Bitmap tempBitmap = new Bitmap(inputBitmap.Width, inputBitmap.Height);
for (int y = 0; y < tempBitmap.Height; y++)
{
for (int x = 0; x < tempBitmap.Width; x++)
{
Color tempColor = maskBitmap.GetPixel(x, y);
if (tempColor == Color.Black)
{
tempBitmap.SetPixel(x, y, inputBitmap.GetPixel(x, y));
}
else
{
tempBitmap.SetPixel(x, y, Color.White);
}
}
}
outputBitmap = tempBitmap;
}
}
The mask bitmap is successfully generated and visible in a picture box, however the color values for every pixel when testing "tempColor" show empty (A = 0, R = 0, G = 0, B = 0). I am aware of the performance problems with getpixel/setpixel, but this is not an issue for this project. I'm also aware that "tempColor == Color.Black" is not a valid test, but that is just a place holder for my comparison code.
I am unable to reproduce your problem. I copy-and-pasted your code and made some modifications to make it work for me. I am able to confirm that tempColor is sometimes #FF000000.
I suspect you mixed up your bitmap references somewhere. Are you really sure you are never getting any value other than #00000000? Do your circleDiameter and circleSpacing have sensible values? And most importantly: are you absolutely sure that you are reading from the correct bitmap?
Here's my version of your code, which I know works:
using System;
using System.Drawing;
namespace Test
{
class Program
{
static void Main()
{
var bitmap = GenerateMaskBitmap(100, 100);
TestMaskBitmap(bitmap);
}
const int CircleDiameter = 10;
const int CircleSpacing = 10;
static Bitmap GenerateMaskBitmap(int width, int height)
{
Bitmap maskBitmap = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
using (Graphics g = Graphics.FromImage(maskBitmap))
{
Brush brush = Brushes.Black;
for (int y = 0; y < maskBitmap.Height; y += CircleSpacing)
{
for (int x = 0; x < maskBitmap.Width; x += CircleSpacing)
{
g.FillEllipse(brush, x, y, CircleDiameter, CircleDiameter);
}
}
g.Flush();
}
return maskBitmap;
}
static void TestMaskBitmap(Bitmap maskBitmap)
{
for (int y = 0; y < maskBitmap.Height; y++)
{
for (int x = 0; x < maskBitmap.Width; x++)
{
Color tempColor = maskBitmap.GetPixel(x, y);
if (tempColor.ToArgb() != 0)
throw new Exception("It works!");
}
}
}
}
}
I am writing to a Graphics object dynamically and don't know the actual size of the final image until all output is passed.
So, I create a large image and create Graphics object from it:
int iWidth = 600;
int iHeight = 2000;
bmpImage = new Bitmap(iWidth, iHeight);
graphics = Graphics.FromImage(bmpImage);
graphics.Clear(Color.White);
How can I find the actual size of written content, so I will be able to create a new bitmap with this size and copy the content to it.
It is really hard to calculate the content size before drawing it and want to know if there is any other solution.
The best solution is probably to keep track of the maximum X and Y values that get used as you draw, though this will be an entirely manual process.
Another option would be to scan full rows and columns of the bitmap (starting from the right and the bottom) until you encounter a non-white pixel, but this will be a very inefficient process.
int width = 0;
int height = 0;
for(int x = bmpImage.Width - 1, x >= 0, x++)
{
bool foundNonWhite = false;
width = x + 1;
for(int y = 0; y < bmpImage.Height; y++)
{
if(bmpImage.GetPixel(x, y) != Color.White)
{
foundNonWhite = true;
break;
}
}
if(foundNonWhite) break;
}
for(int y = bmpImage.Height - 1, x >= 0, x++)
{
bool foundNonWhite = false;
height = y + 1;
for(int x = 0; x < bmpImage.Width; x++)
{
if(bmpImage.GetPixel(x, y) != Color.White)
{
foundNonWhite = true;
break;
}
}
if(foundNonWhite) break;
}
Again, I don't recommend this as a solution, but it will do what you want without your having to keep track of the coordinate space that you actually use.
Just check the value of these properties
float width = graphics.VisibleClipBounds.Width;
float height = graphics.VisibleClipBounds.Height;
A RectangleF structure that represents a bounding rectangle for the visible clipping region of this Graphics.
This is supposed to calculate the histogram of an 8-bit grayscale image. With a 1024x770 test bitmap, CreateTime ends up at around 890ms. How can I make this go (way, way) faster?
EDIT: I should mention that this doesn't actually compute the histogram yet, it only gets the values out of the bitmap. So I really should have asked, what is the fastest way to retrieve all pixel values from an 8-bit grayscale image?
public class Histogram {
private static int[,] values;
public Histogram(Bitmap b) {
var sw = Stopwatch.StartNew();
values = new int[b.Width, b.Height];
for (int w = 0; w < b.Width; ++w) {
for (int h = 0; h < b.Height; ++h) {
values[w, h] = b.GetPixel(w, h).R;
}
}
sw.Stop();
CreateTime = (sw.ElapsedTicks /
(double)Stopwatch.Frequency) * 1000;
}
public double CreateTime { get; set; }
}
The basic histogram algorithm is something like:
int[] hist = new hist[256];
//at this point dont forget to initialize your vector with 0s.
for(int i = 0; i < height; ++i)
{
for(int j = 0 ; j < widthl ++j)
{
hist[ image[i,j] ]++;
}
}
The algorithm sums how many pixels with value 0 you have, how many with value=1 and so on.
The basic idea is to use the pixel value as the index to the position of the histogram where you will count.
I have one version of this algorithm written for C# using unmanaged code (which is fast) I dont know if is faster than your but feel free to take it and test, here is the code:
public void Histogram(double[] histogram, Rectangle roi)
{
BitmapData data = Util.SetImageToProcess(image, roi);
if (image.PixelFormat != PixelFormat.Format8bppIndexed)
return;
if (histogram.Length < Util.GrayLevels)
return;
histogram.Initialize();
int width = data.Width;
int height = data.Height;
int offset = data.Stride - width;
unsafe
{
byte* ptr = (byte*)data.Scan0;
for (int y = 0; y < height; ++y)
{
for (int x = 0; x < width; ++x, ++ptr)
histogram[ptr[0]]++;
ptr += offset;
}
}
image.UnlockBits(data);
}
static public BitmapData SetImageToProcess(Bitmap image, Rectangle roi)
{
if (image != null)
return image.LockBits(
roi,
ImageLockMode.ReadWrite,
image.PixelFormat);
return null;
}
I hope I could help you.
You'll want to use the Bitmap.LockBits method to access the pixel data. This is a good reference on the process. Essentially, you're going to need to use unsafe code to iterate over the bitmap data.
Here's a copy/pastable version of the function I've come up w/ based on on this thread.
The unsafe code expects the bitmap to be Format24bppRgb, and if it's not, it'll convert the bitmap to that format and operate on the cloned version.
Note that the call to image.Clone() will throw if you pass in a bitmap using an indexed pixel format, such as Format4bppIndexed.
Takes ~200ms to get a histogram from an image 9100x2048 on my dev machine.
private long[] GetHistogram(Bitmap image)
{
var histogram = new long[256];
bool imageWasCloned = false;
if (image.PixelFormat != PixelFormat.Format24bppRgb)
{
//the unsafe code expects Format24bppRgb, so convert the image...
image = image.Clone(new Rectangle(0, 0, image.Width, image.Height), PixelFormat.Format24bppRgb);
imageWasCloned = true;
}
BitmapData bmd = null;
try
{
bmd = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly,
PixelFormat.Format24bppRgb);
const int pixelSize = 3; //pixels are 3 bytes each w/ Format24bppRgb
//For info on locking the bitmap bits and finding the
//pixels using unsafe code, see http://www.bobpowell.net/lockingbits.htm
int height = bmd.Height;
int width = bmd.Width;
int rowPadding = bmd.Stride - (width * pixelSize);
unsafe
{
byte* pixelPtr = (byte*)bmd.Scan0;//starts on the first row
for (int y = 0; y < height; ++y)
{
for (int x = 0; x < width; ++x)
{
histogram[(pixelPtr[0] + pixelPtr[1] + pixelPtr[2]) / 3]++;
pixelPtr += pixelSize;//advance to next pixel in the row
}
pixelPtr += rowPadding;//advance ptr to the next pixel row by skipping the padding # the end of each row.
}
}
}
finally
{
if (bmd != null)
image.UnlockBits(bmd);
if (imageWasCloned)
image.Dispose();
}
return histogram;
}