As most college students have learned, posters are an easy, non-destructive, and effective way to decorate. In short, they are awesome. Wouldn't it be great if you could get that same poster for almost free, and with the exact picture you wanted? If you have access to a printer, you can! Websites like Block Posters allow you to upload a photo and have it split into printable pages that can be put together to make a wall poster of any size. The following describes how to do the same task the real way -- using Adobe Photoshop -- allowing you to make wall posters with much more control and of higher quality.

The first step in making a poster is always selecting the paper. Although plain paper will work, photo paper is relatively inexpensive and gives a much nicer finished product. Sam's Club sells a 200-sheet box of double-sided matte photo paper for just $20 ($0.10/sheet). Even if you purchase online, deals like this Merax Glossy Photo Paper aren't hard to find and are still affordable ($5.98 with free shipping for 20 sheets, $0.30/sheet). The real reason for starting with the paper selection, however, relates to math. As true borderless printing is not a reality, we must account for margins when splitting our image across multiple pages. Take your paper size and subtract a 0.25" margin from all sides to get the size of the printable area. For example, I'm using photo paper that is standard 8.5" x 11" letter size, so the printable area of each sheet is 8" x 10.5".

Next, decide on the size for your finished wall poster. Here I'm going to make a 9-page landscape poster (3 x 3), so the total printable area of the poster will be 31.5" x 24" (10.5" x 3 for the width, 8" x 3 for the height).

It is finally time to load up an image in Photoshop. I'll be using this photo I took of the Arc d'Triomphe; feel free to follow along. Select Image > Image Size and resize the image to the total printable area you just calculated. You'll want to keep the aspect ratio constant to avoid distorting the image, so it may be necessary to resize the image to something larger than the total printable area (for example, my photo was resized to 32" x 24", because the other alternative of 31.5" x 23.625" was smaller than the printable area). Before clicking OK on the resize dialog, adjust the Resolution to 150 pixles/inch if it is not already at or above this number.

If your image is not the exact same size as your total printable area, which is usually the case, crop your image. Grab the Rectangular Marquee Tool (M) and change the Style dropdown to Fixed Size. Type in the total printable area in the width and height fields. Click anywhere on the image to position the marquee around the portion you wish to keep. Select Image > Crop to perform the cropping.

Now it is time to divide the photo into individual pages. Grab the Slice Select Tool (K). Click anywhere on your image to select slice 1 (the default slice), then click on the Divide button. In the Divide Slice wizard, you'll want to divide your image both vertically and horizontally, one slice per page. For my 3 x 3 sheet poster, I divided my photo into 3 slices down and 3 slices across for a total of 9 slices.

The last step is to save each slice to an individual file. Select File > Save for Web. You will get a warning telling you that the image is very large, just choose Yes to continue anyway. When the Save for Web wizard appears and begins to generate the optimized image, press the Esc key on your keyboard to stop the process (remember the warning?). Now press Ctrl + A to select all of the slices. From the dropdown on the right side of the wizard, select PNG-24. Now simply click on the Save button. Type a name for your poster, select Image Only (*.png) from the Save As Type dropdown, and click Save again. Each slice (each page) has now been saved in its own PNG image file. These files can be printed exactly as-is and arranged to create a wall poster.

The real reason to use Photoshop instead of a one-click website is because it allows you to combine multiple images into a single montage wall poster using the Contact Sheet feature. Because the end result is much cooler, this requires much more math. You'll need to put all of the pictures to be used in the montage into a new folder. [Note: Don't use pictures with different aspect ratios. You'll need to make a new folder for each aspect ratio and repeat this entire Contact Sheet process for each folder.]

For simplicity, I'll be making a 2 x 1 poster (total printable area: 21" x 8") using a few of my favorite Boy On A Stick And Slither comics. Feel free to follow along by downloading this ZIP file containing 12 comics. The comics are square, and if I place 6 comics across, the dimensions of each will be 3.5" x 3.5" (21" / 6 = 3.5"). With 2 rows of 6 comics, the height will be 7". We'll call this 21" x 7" measurement the total montage area.

Armed with your calculations, launch Photoshop and select File > Automate > Contact Sheet II. Change the Use dropdown to Folder and then click the Browse button to navigate to the folder containing your images. For the document size, enter the size you calculated for the total montage area (here that is 21" x 7") and a resolution of 150 pixels/inch. Also from the calculations, enter the correct number of rows and columns in terms of images -- 6 x 2 in this example. Uncheck Use Auto Spacing and set both the Vertical and Horizontal spacing to 0. Also uncheck Use Filename As Caption and you are finally ready to click OK. A contact sheet will be created; examine it carefully to ensure that the images tile seamlessly with no white space.

Before going any further, you'll need to select Image > Canvas Size and resize the document to the total printable area (21" x 8"). After entering the number in the Canvas Size wizard, place the Anchor in the top-left corner and press OK. At this point, follow the instructions as above for creating a single image poster, diving the document into 2 vertical slices.