How to customize the shapes when rasterizing photos

Question

I want to be able to rasterize photos yet define the exact size and shape of the dots being used.

The closest I get to my desired result is using bitmap → 50% Threeshold in photoshop. The problem with this approach i twofold:

1. I can't change the shape of the positive values
2. I can't put vertical and horizontal space between the shapes
3. I have little control over the actual size (in mm) of the dots.

The following screenshot should better visualize what I’m trying to do:

• Top: Original Image
• Middle: Photoshop → 50% Threshhold
• Bottom: Desired result

Thank you for your help Much appreciated! Best

PS: If there's a way to achieve the same with vectors, that would be even better

Answer 1

There's no way to do that using the threshold filter alone. There's no single effect that will do this, but it's possible using a combination of techniques.

Anyway, here's one possible method using Photoshop.

1. Start with the original image of the mountain, and add a background layer under it filled white.

2. Make sure the mountain layer is selected in the layers panel, and do Filter > Pixelate > Mossaic to make the square pixels, and take a note of the cell size (write it down). The cell size you choose will depend on the size of the original image. For me, the cell size was 36 pixels. Feel free to choose any cell size you want. The result should look something like this:

3. Do a Threshold adjustment to make it all just black and white squares like this example:

4. Using File > New, create a new custom size image, set the X and Y dimensions the same size as the cell size you wrote down earlier, and make sure it is filled black.

5. Using the Elliptical Marquee tool, select a circle in the middle of it, and fill it white. Then select all, and do Edit > Define Pattern. Give the pattern a name you can easily remember. Close this image without saving it, since you no longer need it.

In this zoomed in example my cell size was 36px, so this image is 36 x 36px. This is the image size I used to make the pattern.

6. Back in the pixelated mountain image, add a layer mask, and make sure the layer mask thumbnail is selected in the layers panel

7. Do Edit > Fill. When the fill dialog opens, set Contents to "Pattern". Under Custom find the pattern you previously saved, you may have to scroll down to the bottom of the list to find it. Select it, and hit OK.

Here's the finished result showing the layer with its mask.

Answer 2

Illustrator is the easier option for this job.

1. Apply your threshold and reduce your resolution to the desired values in Photoshop. Take note of the size of your image in pixels (25 x 17 in your example).
2. Copy a flattened raster version of this image and paste it in Illustrator. Yes, it's tiny.
3. Select the object and choose Object > Create Object Mosaic.... In the dialog box, enter the original image's resolution under the 'Number of Tiles' values and click OK.
4. Enlarge the result a few hundreds of percents so sizes in step 6 become workable;
5. Ungroup the result;
6. Select all of the tiles and choose Effect > Convert to Shape > Ellipse... and choose an 'Absolute' size of eg. 1mm by 1mm.
7. Click OK and be happy.

Do note that the resolution reduction and the threshold in Photoshop are optional. Any embedded (as opposed to placed) raster image can be converted into a mosaic right off the bat.

^{_{Credits go to user56... and their awesome answer to this question.}}