Modern digital technology makes it possible to create poster-sized pictures from your photographs. This feature comes in handy especially if you have some old print photos that you'd like to convert to posters to create artwork or even a very large mural for your walls. After using a flatbed scanner and some computer software, your photos will be large enough to be printed out and framed or mounted on poster board.
Scan the photos into your computer at a high dpi (dots per inch). Although 600 dpi might seem too high a resolution number, scanning the photos at this resolution will give you more leeway when you blow them up.
Save the scanned file on your computer in a file folder you've created for the task. This will help you keep all of your photos in one place in the event that you have more than one photo to work with.
Open up your photo editing software. Some common ones include Adobe Photoshop and Corel as well as Microsoft Paint. To enlarge the photo you usually need to look at the top bar for a heading like "Image." Each program works slightly differently, but look around until you see the option to resize the picture. If there's a "resample image" option click on it to take away the check mark.
Change the resolution from 600 dpi to about 300 dpi and notice the print out proportions that result from that change. Ensure that they are at or can be poster size if they're cropped down. They should become larger with the change in the resolution. Save your work.
Crop the photo if necessary so that it fits standard poster sizes like 40 cm x 50 cm (16-inches x 20-inches), 45 cm x 60 cm (18-inches x 24-inches) or 50 cm x 75 cm (20-inches x 30-inches).
Save the photo in a JPEG, Tiff or PDF format to send to the printer. Burn to a disc or send the picture file to the printer via e-mail or via the printer's website if they have a file share/ upload option on their site.
The files from most digital cameras in their most basic form are quite large and usually span over 75 cm (30 inches), but only have a dpi measurement of about 72, which works fine for on-screen, but doesn't print out well. To convert these files, you must do the reverse of the scanned picture files, which require that you reduce the dpi. In this case, you can to change the dpi in the "image" menu to 150 to 200 dpi so that the photo will still be large enough and look good when printed out.
Photos with too small a resolution will look grainy or even blurry when printed out. Make sure to change the resolution before printing.