Updated : 2021
Filter menu in Affinity Photo
Distort
Pixelate filter
Set quantilisation
Click apply
The pixelate filter for Affinity Photo can be found in the distort sub menu of the filters menu list. It is a fairly basic filter for square designed designs but as with all filters, you can manipulate the results in countless ways by using other filters or repeating the pixelate filter over and over.
Sadly there is no blending mode option for the pixelate filter but a quick workaround to that is to duplicate the existing layer.
layer menu
duplicate
filters menu
distort
pixelate
set value
click apply
go to the layers panel
change blending mode for the duplicate to darken etc
All kinds of interesting combinations can be generated by using multiple layers with multiple blending modes and different settings of quantisation.
You don't have to use the pixelate filter in Affinity Photo just once or only that filter, you can combine the filter with others such as blur. You can also re-color the result using live adjustment layers such as curves
filters menu and blurs
gaussian blur
set to 45 etc
apply
filters menu
distort
pixelate
set value
click apply
layers menu
new adjustment layer
curves adjustment
set value
close panel
The result can be a lot softer pixelate. You can, of course, then apply a blur to the pixelate depending on the result required. Or perhaps use adjustments
You can create all kinds of interesting color effects by using the channels panel
view menu and studio
channels
select composite red
apply pixelate filter and different setting
select composite green
apply pixelate filter and yet another setting
etc
click round arrow in channels to return to RGB
You can also just create a selection and feather that selection and use that with the pixelate filter. So if you have a face in an image and only want to obscure the face then simply select the selection tools and select that area and apply the pixelate filter
select the elliptical marquee tool in the toolbox / toolbar
create a selection over the face etc
select menu
feather
set radius and apply
filters
distort
pixelate filter
apply setting