The Photoshop Pointillize filter can be found in the filter menu and Pixelate category.
There is only one setting and that is cell size. Keep it low for a grain like effect or set it to the maximum for chunky spots based on the color in the image.
It also uses the background color as the background for the effect (so if you use red as the background in the toolbox then you will see a reddish effect, if you use blue, you will see a more bluish effect. You can change the background color to black or white or green etc via the toolbar and background color and then the image will end up lighter or darker or greener or black etc.
You can apply it multiple times. You maybe happy with the result after the first apply but some work even better after a couple of applies as well as combining with others such as Gaussian. If you keep re-applying using the repeat feature found at the top of the menu then most often or not, the image will change but the size of the dots will not but thew colors will shift around a little.
You can also fade the effect via the edit menu and fade command and opacity / blending modes can be added such as using the effect in difference or darken against the original supplied image.
You can also use it with layers as well as with smart objects and you can blend the layers with blending modes etc. You can also combine the effect with others
You can also use the effect with selections, you can use the rectangular marquee etc as well as selection tools via the select menu such as color range. You can then use the selections as a great source of transparency which can be used with layer styles etc to add bevels as well as drop shadows and more
It can also be used with view menu and pattern preview even though the pattern preview will show an error.
You can apply others such as the twirl and then the effect to create an interesting twirl dot effect. You can also apply them the other way around with the Pointillize first followed by twirl or the maximum or glass etc
It can also be recorded. Select an image and then go to the window menu and actions and then go to the record button on the panel and record the steps of the effect along with others such as the cutout etc and then stop the recording. This action can then be played back at any time. You can create all kinds of amazing effects with the feature especially combined with maximum effect as well as oil paint etc such as creating abstract and swirly flowing designs
You can select any shape and turn the design into a smart object and then use the effect on that or if you wish, you can use the layer menu and rasterize on the shape (any shape) and then apply the effect. You can apply it once or multiple times. You can also have different spot settings for each added. The great thing about this non destructive effect is that you can edit by double clicking the entry and then tweak the settings and also you can disable it any point.
You can also use the effect with channels. Go to the channels panel and then select the red channel and then apply the effect with one setting, go to the green and apply with a different and then restore back to RGB etc.
Create a layer via the layer menu and new. Go to the gradient tool and select a preset and apply in radial style Go for one of those super colorful gradients such as blue red yellow default preset. Set the background in the toolbox to a color that is not in the gradient so if it is blue red yellow, black will be a good choice or white as you will need something to select as the transparency is not added to the effect by default (that would be a useful feature). Apply the effect as mentioned above and set a cell size of 40 or so and click OK. You should now have lots of spots etc on a very black background. Go to the magic wand tool in the toolbox and select a black area and then go to the select menu and select the similar command and all the blacks should be selected. Invert the selection via the select menu. Edit menu and copy and then follow by paste and you will have a new layer with your effect only (that is why I would love to see all the new output features extended to these older tools). Go to the layers panel and then click fx at the bottom and select the bevel and add some depth to your design. You can also create multiple copies of the original and create a number of combinations of the effect and blend them together using blending modes. Flatten the image if you wish.
You can use the find edges effect (stylize category) combined with the effect. You can vary the cell size and then just apply the find edges. The result will be an abstract design of colorful lines. If you want, you can always apply an adjustment layer such as black and white to make the lines black and white. Apply the find edges multiple times and the lines will end up fairly black and thick. You can then run the stylize menu oil paint to smear the lines to create an interesting cellular texture design