Here's how you might approach this task in C#:

### Step 1: Load an image

```csharp

using System.Drawing;

using System.IO;

// Replace 'path_to_image.jpg' with your actual file path and name.

Bitmap bitmap = new Bitmap('path_to_image.jpg');

```

### Step 2: Convert the image to a string of ASCII characters

This part involves iterating over each pixel in the image, converting its color values into an equivalent character from our predefined set. Here's how you might implement this:

```c

static char',' ImageToASCII(Bitmap bitmap)

{

int width = bitmap.Width;

int height = bitmap.Height;

// Create a 2D array to hold the ASCII characters for each pixel.

char', ' result = new char'height, width';

// Define our set of valid character codes (0-128).

const string asciiChars =

'@%#&$@&!()*)'`~<>?_+=-*#^|{'}'/\\:;\'\' ,./';

int'' rmap = new int'256';

for(int i=0;i<256;i++)

{

if (i >= 32 && i <= 126)

rmap'i - 32' = asciiChars'(i - 65) % asciiChars.Length'.ToInt();

}

// Iterate over each pixel in the image, converting its color value to an ASCII character.

for(int y=0;y

{

int dy = (int)((double)y / height * (asciiChars.Length-1));

string s = '';

for(int x=0;x < width; ++x)

{

Color pixelColor = bitmap.GetPixel(x, y);

byte r = pixelColor.R;

byte g = pixelColor.G;

byte b = pixelColor.B;

// Map each color component to a value between 0 and 127 (inclusive).

int v_r = Math.Max(0,Math.Min((int) ((double)r / 255.0 * 127.0), 126));

int v_g = Math.Max(0,Math.Min(((double)g/255.0)*127.0 ,125));

int v_b = Math.Max(0,Math.Min(((double)b)/255.00*123.0,122));

// Convert the color value to a character from our set.

s += rmap'v_r + 32';

}

result'y,x'=char.Parse(s);

}

return result;

}

```

### Step 3: Print out your ASCII art

Finally, you can call `ImageToASCII` with any image file and it will output the corresponding ASCII representation to console:

```csharp

Bitmap bitmap = new Bitmap('path_to_image.jpg');

char',' asciiArt = ImageToASCII(bitmap);

// Iterate over each row of pixels in our 2D array.

for (int y=0;y

{

// Print out the characters for this row, followed by a newline character.

foreach(char c in asciiArt'y')

Console.Write(c);

Console.WriteLine();

}

```

Remember to replace `'path_to_image.jpg'` with your actual file path and name.

This will output the ASCII representation of an image directly to console. You can easily modify it to save this as text or even display it graphically if you prefer!

Characters for ascii art