Check if exact image in exact location is on screen - image

Question

I am looking to create a program in Visual Studio (C#) which scans the screen for an exact image in an exact location of the screen. I have seen many discussions which involve algorithms to find a "close" image, but mine will be 100% exact; location, size and all.
I have obtained a png from a section of my screen [Image 1] using this code:
private void button1_Click(object sender, EventArgs e)
{
//Create a new bitmap.
var bmpScreenshot = new Bitmap(Screen.PrimaryScreen.Bounds.Width,
Screen.PrimaryScreen.Bounds.Height);
// Create a graphics object from the bitmap.
var gfxScreenshot = Graphics.FromImage(bmpScreenshot);
// Take the screenshot from the upper left corner to the right bottom corner.
gfxScreenshot.CopyFromScreen(1555, 950,
1700, 1010,
Screen.PrimaryScreen.Bounds.Size,
CopyPixelOperation.SourceCopy);
// Save the screenshot to the specified path that the user has chosen.
bmpScreenshot.Save("Screenshot.png");
}
So, basically here is the flowchart of my program on how I want to move forward:
1) create the master png using the above code
2) run loop:
create same screenshot using the same procedure as the master png
compare master png to new screenshot png and if:match then move on otherwise reiterate loop.
I am very new to programming, but I don't believe this is beyond me, given a little guidance. I have written fairly complicated (in my opinion) VBA and Matlab programs. Any help is greatly appreciated.
Thank You,
Sloan

Answer 1

Digging around a bit through Microsoft's documentation, I came up with a rough function that would do something similar to what you want.
https://msdn.microsoft.com/en-us/library/hh191601.aspx
This function offers the chance of getting stuck in an endless loop, so you might consider calling it with a timeout from your main. See here for info on synchronous methods with timeouts:
Monitoring a synchronous method for timeout
From your main, all you'd have to do is see if it returns true.
static int Main(string[] args)
{
if (ImageInLocation(left, right, top, bottom)) {
// do other things
}
return 0;
}
The only thing I'm not entirely sure on is how strict you can be with the ColorDifference. Even if the images are identical, any pixel difference with an entirely non-tolerant ColorDifference will come up false. If you know it should work and it's not, perhaps consider increasing the tolerance. Here's some more info on that:
https://msdn.microsoft.com/en-us/library/microsoft.visualstudio.testtools.uitesting.colordifference.aspx
public bool ImageInLocation(int left, int right, int top, int bottom) {
bool image_found = false;
var masterImage = Image.FromFile("path_to_master");
while (!image_found) {
// screenshot code above, output to "path_to/Screenshot.jpg"
var compImage = Image.FromFile("path_to/Screenshot.jpg");
// note, all zeroes may not be tolerant enough
var color_diff = new ColorDifference(0, 0, 0, 0);
Image diffImage;
image_found = ImageComparer.Compare(masterImage, compImage, color_diff, out diffImage);
}
return true;
}
Good luck! Welcome to the programming community.
Also, if anyone has any suggestions/changes, feel free to edit this. Happy imaging, friends!