tile_size setting in shortcode

The tile_size attribute is meant for optimization of image loads – it has very little bearing on your layout.

An original image from Google might be 6000px wide, so if you had 100 such images, you would end up adding 500MB+ to your page’s load, which would considerably slow down your page. The tile_size is intended to help you save some resources when you load the images. A tile size of 450 will tell Google to serve an image that is 450px, which will result in an image that is about 1% of the original 6000px image. This would mean that your images will only add about 5MB to the total load of the page.

The minimum tile height is what governs the layout – it ensures that your images in the justified grid are never less than the minimum height. Now, if you have used a tile size lower than the minimum tile height, that will cause pixelation of the images.

Yes, that’s correct. The “dumb” grids like the square thumbnails let you pick individual sizes. The automatic layouts don’t let you define a custom size, since all the calculation is algorithmic.