There is much confusion about the correct resolution of a high quality photo that is expressed in dpi. Searching with Google for the keyword ‘dpi’ results in a long string of questions. DPI is however very important when preparing an image for sublimation on ChromaLuxe: the more DPI, the sharper the result.
DPI is a confusing concept: when we talk about printing, it means the resolution in Dots Per Inch. When we talk about cameras or monitors, we talk about the resolution in Pixels Per Inch. To make it even more confusing, here in Europe we talk about Pixel Per Centimeter.
So what is Dots Per Inch? DPI is the total amount of dots that can be placed in a line within the span of 1 inch (25,4 mm).
You can find the properties of your digital photos in a photo editing application like Photoshop, but also in Windows Explorer. These properties are called the EXIF (data). To find those properties in Windows, do a right click on your file and after that Properties > Summary > Advanced. In Apple Finder, just click on the photo icon, the press Command-I to bring up the info dialog. When it appears, click on the right-facing triangle beside the word More Info.
If you are a professional photographer or printer, you need to open your images in Photoshop to know the exact size that your image can be printed on. There is only one rule: your image must have 300 Pixel/Inch to have perfect sharpness and detail. To find out, go in Photoshop to the Image menu and choose Image Size. Change Width & height to Centimeters and be sure that Resolution is set to Pixel/Inch. Check if the Resolution is 300 Pixel/Inch to know the dimensions in Centimers (right image in the example below is faulty).
What to do when your original image is only 72 Pixels/Inch ? Well, than you need to Resample it. To do this, go in Photoshop again to the Image menu and choose Image Size. Untick the Resample-checkbox and type next to it 300 (check example below). Width & Height will show you now the exact size that your image is printable. Save it this way and start to print.
What happens when my image has a low resolution but has the correct dimensions ? The image will look great on your screen, but… once it’s printed you will see the pixels very strongly. If a high resolution image is not available, you can try to lower the resolution. You can go as low as 150 PPI for printing with the sublimation technology. Don’t go lower, because you will start to see pixelation (check example below). Another trick is to blow up your image. You can do this with Photoshop, but you have also 3rd party applications (e.g. blow-up3 from AlienSkin). The trick is not to blow up your image in one time, but to do it in several steps (4-5 times).
Not sure if your dpi is sufficient? You photolab will be able to give professional advice. When you are sublimating yourself, always follow this rule: more dpi is better. Play with it and experiment, you’ll soon understand the value of dpi!
Steven Roesbeke has a huge experience in the graphical industry with a lot of expertise in color management and output solutions. Since 2013 he is the Technical Support Field Engineer at Universal Woods EMEA. Read his technical blog posts to discover helpful tips & tricks and learn more about the do’s and dont’s of (large format) sublimation. You can always contact him at firstname.lastname@example.org