Image Resolution 101 2018-06-13T21:20:16+00:00

Image Resolution 101

How and Why to Change Resolution in Photos and Images

We receive dozens of images from customers asking if they can be enlarged. Most of these images are obtained from websites or scanned in from a magazine. Images need to be at least 200 dpi (dots-per-inch) for purposes of enlargement, and 300+ dpi is even more recommended. (On a computer screen this is really PPI or pixels-per-inch. DPI or dots-per-inch technically relates to a printed picture. Most people just say DPI when referring to either situation.)

Digital images can appear beautiful to the eye and still be very “lossy” in their actual content. “Lossy” means that the image is saved in a format that is stripped of a major amount of content. The popular JPG and GIF image formats are known as “lossy” formats because it is easy to decrease the substance of images down to the smallest possible size that still “appears” satisfactory. Images in these formats can appear substantially attractive to the human eye and still have a lot of their image information stripped out of them. This is done so that their file size is smaller and they load on web pages quickly.

Images scanned in from magazines or newspapers are always low-resolution images. Magazines especially show evidence of this.  Magazines are printed to save ink by finding the balance between what appears adequate – even very pleasing – and what can be printed at the lowest ink cost.

Take a look at this image. It appeared to be an image that we could enlarge big enough to build a floor-to-ceiling wall mural with YottaPrint. We scanned it from a paper photograph using a high-end scanner at 600 dots-per-inch, a resolution so high that it made the file size very large. Most people would think scanning at 600 DPI would produce a high resolution, pleasing result when the photo was enlarged. However such is not the case . . .

When this original is enlarged, the lossiness of the original is evident because it was scanned from a printed or paper source. Since the original was a low-resolution image, there simply was not enough information in the photo to enlarge it satisfactorily, even though it looks presentable on a computer or device screen.

Original image scanned at 600 DPI

In these next two examples you can clearly see what the human eye missed: dots in the original that are not visible until the image is enlarged.

Image scan raw dots showing in photo enlargement

This image is the raw (unprocessed) enlargement of the original image scan. As you can see, when a low-resolution image is enlarged, even the best-scanned image using the best photo enlargement software (Imagener, of course) is only enlarging content that simply does not exist – pulling apart what is there and revealing what is not.

Image enlarger result of high resolution paper scan

This image is the result of the first scanned image processed through the Imagener image enlarger. The high-resolution scan served to create a really detailed image of the dots that the scanner could “see,” then the enlargement process perfectly enlarged the dots. Images taken from websites can often be much worse than this, completely coming apart into large blocks when enlarged. This is because in their original form they may look okay, but the human eye is really looking at very little actual digital content.

Again, the original image in this example was scanned in at an extremely high resolution – 600 dpi – but the beginning image just did not have sufficient content for image enlargement purposes even though the human eye sees a beautiful picture in its original form. If in this case the picture we scanned had been a glossy actual photograph with at least 300 dpi resolution, the image could have been enlarged or used to create a beautiful wall mural.

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