Blowing up digital images.
How big can you blow up my picture? This is the most often asked question and the least understood by most amateur (and even pro) photographers. So I will attempt to answer in the most layman’s terms that I can, but there is some technical nomenclature that everyone should at least have a grasp of that I will spell out throughout this article.
What makes a good image? PIxels and lots of them. Every digital image is made up of dots or pixels. The number of pixels in an image is determined by the megapixels in your camera. For example if you have a 12MP camera then you will get twelve million pixels in each image you shoot. You can actually see them if you zoom in far enough in Adobe Photoshop (like 1200%). See below original and zoomed in image.
The more the pixels in a tighter space the higher resolution. For example 300dpi vs 72dpi or 300dots per inch is much better than only 72 dots per inch. This gives Adobe Photoshop a lot of information to work with and thus makes it easier to blow up images to larger sizes with out losing as much clarity in the details.
However it is true that as you make images larger in Adobe Photoshop you are reducing the the dots per inch (dpi) and thus losing clarity in your image. So theoretically the larger you blow-up an image in Adobe Photoshop the worse the image becomes. This is because you are using the same finite number of pixels to make an image larger.
See below example of same image at a resolution of 300dpi and 72dpi Notice how it effects the size of the image in inches, i.e. from almost 10×14 to a little over 40×60. However the pixel count never changes.This image is always made up of the same number of pixels. 4368×2912=12,719,616 or over 12 million pixels. What this means is that if we print this as a 40×60 the quality of the print would not be nearly as good as if we printed at the smaller size. Print images need to be at 300dpi to ensure a high quality print of a digital image.
So how do we retain great clarity when blowing up images? Easy, make more pixels and make them match the image as much as possible.Software programs like OnOne Software’s Perfect Resize can maintain the quality of the image the larger you go. How is this done you ask? well the program runs algorithms and does interpolation that look at every pixel and reproduces more pixels that duplicate the ones that are there.
This screen shot of the interface from Perfect Resize shows that if we want to take the 300 dpi image and maintain that dpi but blow up from the old size of 9.7×14.5 to a 16×24 size, then we will be blowing this image up 164% and it will be 7200 pixels wide by 4800 high. (if you recall it was previously 4368 x 2912. So the difference in pixels is what has to be made up by the software and put into the image. Again, this is what makes large format images retain their clarity.
Try to keep in mind a simple rule and know the difference in resolution.
Garbage in Garbage out: This old-school rule pretty much sums things up. If you give me a lousy image to start with then the results will be lousy. However, if you give a good image to start with then we can go places. So the higher the resolution you have the better.
Web vs Print: Web images are generally at resolution of 72dpi and print images are at 300dpi. Web images need to be smaller in file size, so they can load quickly. 72dpi is kind of the lowest in quality you would want to go before images really start to look bad. However, when you are printing an image you want a much higher resolution (and thus higher file size) in order to get all the details in your print.
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