Creating a Photo Mosaic with Photoshop
Creating a mosaic in Photoshop is a simple process. For this example, we will need three photos. The first will be the main photo that takes up the whole frame. The other two will be tile pieces that will appear to assemble into the main photo. So, we will assume you have a picture of a cat which you want to be made up of bird and fish pieces.
Step 1: Setting up Your Main Image
The easiest thing to do is to make the cat photo a perfect square so that your pattern has an even edge on all four sides of the image. So choose your Rectangular Marquee tool, hold down shift to keep both axes equal, and drag a square over the part of the image that you want. Then, go to "Image" and select "Crop". Now, go to "Image" and check the "Image Size". Find out how many pixels make up the width and height of your photo. Divide the width of the main photo by the number of tiles you want in each row. For the sake of explanation, we will assume that the resulting number is 10.
Step 2: Setting up Your Tile Photos
Open one of the other photos, for instance, that of a bird. Select your crop tool and look at the top option bar. Tell it to crop to the size that you want each tile to be, in this case 10 pixels wide and 10 pixels high. You can drag the crop tool over the image selecting as much as you want and still Photoshop will make the image 10x10. Do the same with the third image, the fish.
Step 3: Creating Your Tiles
Create a new Photoshop document. When asked to define the size, double the number you came up with in step 1, in this case 10 doubled is 20, and enter it as both the width and height of your new document. Now select the move tool. Go back to the photo of the bird and click on it; the bird should disappear. Come back to the new blank image and click on the canvas. The bird is now in the new document; drag him to the top left corner. Next, while holding Alt, click and hold on the bird and drag the newly created copy into the bottom right corner. Move the fish in the same way you moved the bird, but use the other two corners. You may notice that you now have 5 layers, so go to "Layer" and choose "Flatten Image". To finish it off, go to "Image", "Adjustments", and select "Desaturate". Now you must store it as a pattern in "Edit", "Define Pattern".
Step 4: Putting It All Together
Return to the main picture, that of a cat. Create a new layer by going to "Layer", "New", and choose "Layer". Now grab your paint bucket tool and in its options bar use "Pattern" and select your pattern. Make sure the opacity is set to 100%. Click anywhere on the image and your pattern will appear. Look at the layer menu and in the drop down select "Overlay". Now you have made a mosaic.
There are many degrees of complexity that you can take this idea to. But, the basic steps will always apply in this stylizing process.
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