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Extra pixels won’t buy you anything but rejection
“The resolution of my Western blot picture is too low…” he said. “I’ve set the correct print resolution for my figure but now that I’ve imported the Western blot picture, I can barely see it. Can I just scale it up a little?”
Modern digital image editing programs make it very easy to scale images up and down. Too easy maybe, because without understanding of what you actually do, you might ruin the quality of your publication figure. This often results in rejection of your scientific paper. Too bad.
There is a short answer to avoid problems down the road: never upscale the original image.
By doing so, you create extra pixels to fill up the empty space. Pixels are the smallest ‘physical’ elements that build up your image on a computer screen. Since you cannot scale a pixel, extra pixels need to be created when you upscale your image. There are many different algorithms of how the editing software approaches this problem, but none of them is perfect. You will always lose quality.
I know that this sounds obvious, but still it is a very common mistake many publishing scientists make. However, most of the time this mistake is not made by simply upscaling the original image, but in a more hidden fashion:
Production-ready article figures require a print resolution of 300 pixels per inch (ppi) for optimal quality. As explained before, I recommend to prepare all your figures at the size they will appear in the journal with the correct print resolution (300 ppi). If you don’t do so and save your figures at screen resolution (typically 72 ppi), you might encounter problems later on. Many scientists make their figures in presentation software such as Microsoft Powerpoint and end up having only 72 ppi.
The next thing that happens is that these figures are opened in imaging editing software like Adobe Photoshop and the print resolution is adjusted to 300 ppi. This is vey easy to do and harmless if you don’t check the ‘resample’ button (see screenshot).
Without resampling, the physical dimensions of your image will become smaller, because you will pack more pixels per inch (from 72 to 300). In this case you don’t create extra pixels and the quality of your image will remain the same. The problem is that now the image might be way too small for publication.
With resampling turned on, the physical dimensions of your image will remain the same, but extra pixels will be created. This results in a lower quality image (often blurred). In this case you basically do the same as upscaling the original image. Don’t do it!
Most of the time there is an easy fix. The problem is almost always caused by using images from Powerpoint and not starting from the original images coming from the camera or capturing device. To start over, just setup your file to match the physical dimensions and the required print resolution (300 ppi). Then import all the images you need into that file. Never upscale the images anymore and you’re good to go. Success!
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