Many of us have used this tool in photoshop plenty of times. As a left brain thinker, I have always wondered what in the heck does Gaussian mean. I’ve also wondered how exactly you pronounce the word. It’s funny to hear how many ways people say it. So, here is the definition from Merriam-Webster: being or having the shape of a normal curve or a normal distribution. Pronounced: gau̇-sē-ən
Well…..that’s clear as mud. However, it does shed some light as to why you pick the radius of the blur you want to use in Photoshop.
After playing with this in Photoshop it makes sense now that as you raise the pixel radius it basically begins to group pixels together. What does that mean? Think of it this way, imagine looking at a single pixel. Now take the 10 closest pixels around it and blend them together using an average of their tones. Now multiply this across an entire image. The result, less overall pixels with less tonal detail which ultimately creates BLUR.
Now lets ramp it up another level. Try taking the radius all the way up to the max. You’ve now basically taken all the pixels in the image, averaged their tonal value and for most images this will result in a solid gray image.
Ever notice that you get more blur on certain images at the same radius? I bet you used a different camera for the two images. Your cameras megapixels will determine the number of pixels you start with. A Sony A7R ii shoots 42.4MP….that’s a ton of pixels! You will have to significantly ramp up your radius to get this image to blur vs an image from something like a Canon 5D iii which shoots 22.3MP.
Here are a some samples to show what is happening (shot with a Sony NEX6 – 16.1MP):