Warning this article contains technical stuff and some mathematics!


Simply speaking, digital photographic images are made up of pixels – tiny squares. The resolution is the number of pixels in a particular image. You can describe the resolution in two ways, the one that I find useful to use is the number of pixel columns (width) by the number of pixel rows (height). Your computer will display the pixel information for a particular photo image.

Photos for Web

Generally, images on the web are small in resolution on purpose, so that they will load quickly. A typical image which has been sized and optimized for the internet might be anything from 75 pixels wide to 800 pixels wide or high (the latter is considered quite large for web).

image 75 ppi
Image 300 pixels by 300 pixels

Photos for Print

A useful rule of thumb to use when printing photographs is a resolution of 300ppi (or dpi – dots per inch – effectively the same thing!) which means 300 pixels per inch. Yes photograph lab printers still use inches! So if you wish to make a 4×6” (10x15cm) print from your photo, just multiply the 4 by 300 to get 1200 pixels along one side, and multiply the 6 x 300 to get 1800 pixels along the other side. (I will make a comment here that a large resolution doesn’t necessarily mean a higher quality image or good sharp focus!)

To figure this out in reverse, you could have an image 600 x 900 pixels which will look great on your phone, tablet or computer screen. To work out what size you should print, just divide the pixel numbers by 300 (most photograph printer’s ideal printing resolution). This photo should best be printed at the size 2 x 3 inches, or 5 x 7.5cm.

Resolution vs Compression

It is important to note that just because an image may have a decent resolution ie, the photo has been scanned at 600 to 800dpi and is over 2MB in size for example, does not mean that it will be excellent quality, with sharp and crisp detail and smooth colour gradations. An image should also have been saved (if a JPG) at best quality, lowest possible compression, or largest file size. This is why TIFF images are often preferred by professionals as the image format supports lossless compression – no image data has been lost during the file saving process. TIFF images are very large however, and in most cases a JPG saved at best quality, largest file size as described above, are easier to transmit digitally and share, and quite satisfactory to work with either for print or restoration. A JPG which has been saved with even a medium amount of compression will show visually unpleasant, blocky, pixellated characteristics.

Enlarging (or upscaling) a photo from a digital file…

It is possible to print a photo bigger therefore enlarging by brute force, for example to print a 600×900 image at an 8×12” size – effectively giving you a resolution of 75ppi. Most people will not be happy with the result! This is when you will see the pixels more clearly, and when the image is described as “pixelated”.

Photos can be enlarged in image editing programmes; Photoshop is one option, but there is a limit to how far the existing pixels can be stretched in Photoshop. An image even 1200 x 1800 pixels will only enlarge so far and a pleasing result will depend as well on whether the photo is well focussed to begin with. Other apps or programmes are now available which will upscale or enlarge digital photos, and can even sharpen and enhance the photo – reducing noise and adding detail where previously there was none.

The below image has been forcibly enlarged from 75 pixels to 600 pixels in Photoshop. This is not a successful enlargement as the original image, though sharp and reasonably focussed, was small and comprised of limited pixels to start with.

Sometimes the upscaling, enlargement programmes/apps can do a better job, sometimes nothing can achieve the desired result, but also sometimes a combination of techniques will be quite successful in enlarging small photos.

The results in these enlarged and enhanced images can sometimes be creepy and unrealistic but sometimes the resulting enhanced photo is absolutely incredible. These programmes, available as mobile or web apps, are a wonderful addition to the photo retoucher’s toolbox. Frequently I am asked to resurrect a sadly tiny, blurred, damaged photo which may the the only one in existance of a long-lost beloved relative or friend, and with the addition of these resources I am often able to provide an amazing result.

An example of an enhanced, enlarged photo here.

Please contact me if you have any enquiries!

Enlarging a printed photo

If a client needs a large print then I will scan the original photo at an extra high resolution eg 1200 or 2400 dpi, saving the photo at minimal or no compression (either TIFF or best quality JPG) and if the photo needs further enlarging from that starting point this will be perfectly possible.

I would like to add the caution that, any enlargement from a small photo to a bigger one, no matter the depth in resolution, if the photo is blurry/unfocussed or even softly focussed to begin with then this will be more apparent in the enlarged photo on close inspection. Usually however the enlarged photo will be displayed on the wall and viewed from a distance so some softness would be quite acceptable.

Please refer to my comments in the previous section regarding enhancing and sharpening blurry photos, with the help of the latest ai enhancement technology, it may be possible to then improve the resulting enlarged photo further.

As always, please contact me if you have any queries or concerns, I am always happy to discuss how I can help you!