Any way to limit values without the use of if statements?

I'm working on a program that works with images. I'm having trouble on a function that adjusts contrast and brightness. I need to calculate a value for each RGB component based on what input I recieve from the user. The problem is, I need to make sure the final value after said calculation isn't greater than 255 or less than 0. So it can fit inside a byte.

temp = c * dataPtr[0] + b; //variable temp is of type double.

if (temp > 255)
{
    temp = 255;
}
else if (temp < 0)
{
    temp = 0.0;
}

dataPtr[0] = (byte)(Math.Round(temp)); 

I'm repeating this for every RGB component of every pixel, so the ifs are getting executed a million times, most of the times needlessly.

I thought about just casting a double back to byte but it just reads the first byte of the double and doesn't max out the value if it's greater than what a byte can handle. Is there any obvious way to optmize this this range-check that I'm just missing? Thank you.