Finding images for a research poster and ensuring they'll look their best when printed can be a tricky process. It's often hard to tell how an image will look when it's printed, especially photos found on the web. You might find an image through Google Images, or a colleague might send you an image to use in a poster, and those images may look fine on a screen. Once added to a poster and printed, however, they come out looking blurry or pixelated. What happened? Why did the pictures come out looking bad when they looked so good on the screen?
Understanding image resolution
The reason that photos you found online might not look great in a poster has to do with an image's resolution. Resolution refers to the amount of spots of color per linear inch of surface, and typically uses the abbreviations dpi (dots per inch, for printing) or ppi (pixels per inch, for screens) to refer to an image's resolution. The higher an image’s resolution (or amount of spots of color per linear inch), the better it will look when printed. When images are created for print, they typically have a high resolution, typically around 300 dpi — which means 300 dots of color are printed on a linear inch of paper. Images for the web are typically created and saved at a lower resolution, since the majority of screens have a resolution of between 72 and 96 ppi. This results in a smaller file size, which means the images load faster — however, this also results in a lower quality file, as there are fewer spots of color printed on the page.
If you download an image from the web and include it in a poster without checking its resolution first, there's a good chance the image will be too small and need to be enlarged to be properly seen on a poster. Let's take a look at an example of a typical image we might find somewhere on the web, a medium-sized photo of a cat.
This image looks crisp and clear — however, the image is rather small. It's only 360 pixels high by 270 pixels wide, and has a resolution of 72 dpi. Let's say you incorporated this photo into a poster, and since it's small, you enlarged it in the page layout program we're using to make it easier to see. After printing out a section of the poster, the image didn't come out looking quite as clear as it did previously:
As you can see in the previous image, the cat photo didn't print out at a very high quality. Instead, it looks pixelated and a little blurry in some spots. How can you avoid including images in a research poster that won't look good when printed, like the cat photo shown previously?
Ensuring your pictures look their best
To make sure your pictures look their best in a poster, you'll need to ensure the images are the size and resolution you need before you start putting them in a poster. Enlarging images once they're in a poster will result in images that look like the previous example. You can find images that will look good in a poster by making sure you're aware of the following things when collecting images: the image's size and it's resolution.
- Image size: Check the image's size - if the image is small, it likely won't print well in a poster. Aim for images of at least 1000 pixels (either for the width or the height) in size.
- Image resolution: Check the image's resolution before placing it into a poster. Images with a resolution of lower than 150 dpi will likely not look good when printed.
If you happen to find images that are large enough in size (larger than 1000 pixels), but have a low resolution, you can edit the resolution so they can be used in a poster. Let's first take a look at how to find images that will be large enough to allow you to adjust the resolution before including them in a poster.
Finding appropriately-sized images on Google Image Search
When searching for images using Google Image Search, you can change your search settings to only return results that include images over a specific size. This can help ensure your images will either have a high resolution or can easily have their resolution raised. Searching for images larger than 1000 pixels should return images that will be of a sufficient size for printing, or will allow for adjustment of the resolution later.
The following steps will walk you through how to set Google Image Search to display only large images in its search results.
Now, Google Image Search will display images where the image is at least 1000 pixels wide or tall. (Keep in mind that these search settings will be reset once you navigate away from the Google Image Search page.)
Google Image Search allows us to view the image's size in pixels by clicking on an image to display the preview, then hovering our cursor over the image preview in the preview panel, as shown in the following example:
As highlighted in the previous image, the image’s dimensions will display in the bottom right corner of the image preview. This can be helpful as you work to find images that are an appropriate size for your poster. As long as you have large enough images, you'll be able to adjust the resolution if necessary.
Working with images from a scanner or digital camera
When scanning images, the scanner's output can be set to a specific resolution using the specific software for the scanner. If scanning an image from a print source, make sure to set the resolution to at least 150 dpi before scanning the image — this will ensure that you won't need to adjust the resolution at a later time.
If you're taking photos with your phone's camera or another digital camera, chances are those images are already large enough that you can change the resolution without making the images too small. Most digital cameras take pictures at anywhere between 12-16 megapixels, or over 4000 pixels wide or tall. This results in an image with a very large print size, but with a low resolution (typically 72 or 96 dpi). These can then be edited down to a more reasonable size by adjusting the resolution.
Changing an image's resolution
Image size and resolution go hand in hand — how large an image appears when printed is based on the resolution of the image. A digital image is made up of a set amount of pixels, and the resolution controls the amount of pixels that are printed on a square inch of paper. For example, an image with a resolution of 300 dpi means that the printer will print 300 dots of color per square inch of paper, which results in a high-quality image. If you have an image with a low resolution, fewer of those dots of color will be printed in a square inch of paper, and the image might look grainy. You can adjust the resolution of an image, within reason — this involves indicating you want to have more pixels printed in a square inch of paper. Before you start the process of changing the resolution, you'll want to make sure your image is large enough to edit the resolution without making the image too small. You can use Photoshop to check the size and adjust the resolution of an image by using the Image Size dialog box.
The Image Size dialog box will appear:
Take a look at the values listed for the dimensions, as well as the width and height – the image we're viewing the details for is very large, with a size of 4032 by 3024 pixels, and a print size of 56 by 42 inches. However, the image's resolution is only 72 pixels per inch, which means if this image were printed as is, it would look grainy. If the resolution of the image is changed, the image will print at a higher quality, and the print size of the image will also be reduced, resulting in a more reasonably sized image.
The first step to take is to make sure the Resample checkbox is unchecked. Resampling an image involves changing the pixel dimensions of the image, either by adding or removing pixels, and can degrade the quality of an image. Unchecking the Resample checkbox makes it so that when an image is resized, Photoshop won't change the number of pixels in an image to make the image a specific size. What Photoshop will do is change the print resolution, instead of removing or adding pixels to the image, to make it a specific size.
Additional tips for working with images
When using images from the web, it's important to make sure that you have permission to use the images you've chosen for your poster. The best way to go about finding images that can be used in posters without potentially violating copyrights is to choose images that have been shared under a Creative Commons license. Google Image Search allows you to search for images that are able to be freely reused. The following accordion fold includes instructions for setting Google Image Search to only return results that are available for reuse through Creative Commons.
Learn more about Creative Commons licensing at the Creative Commons homepage.
Here are a couple of additional tips to help you when working with images for a research poster:
- Keep backups of the original image files. If you're significantly editing an image, or if you're unhappy with the final results of editing an image, keeping a copy of the original will be helpful if you want to start the editing process over again.
- Save your files in a print ready format. The TIFF (.tif) file format is ideal, but if you're using PowerPoint to create a poster, you can also use JPEG (.jpg) files as well. You can easily save the files in a new format when you're done editing the image.
- If you need additional help with editing images for a poster, check out the course Photoshop: The Basics for guidance with working with Photoshop to edit images.