Change the default Eye-dropper sample setting
The sample size of the Eyedropper tool (I), found in the Options Bar, controls the size of the area that’s evaluated when it provides color and tonal feedback, but it can also affect how certain selection tools work,e.g., the Magic Wand or the Color Range command. The default Sample Size value is Point Sample, which samples a single pixel; however, this isn’t ideal for photographs, where using 3 by 3 Average or 5 by 5 Average will give you better results.
and how can eyedropper size be increased