What is the process involved in photograph enlarging and how does it work? This post examines the ins and outs of one of one the fundamentals of image processing.

Photograph enlarging is often requested in photo restoration. Old photos are often small and wallet sized. These battered and torn photos can be enlarged so we can see more but with that comes a few complications. Let us first look at the most important step of enlargement, scanning.

Step 1 – Scanning

To enlarge a photo the most important step is scanning. First we need to know how big we want the image to be printed. If we have a pass port photo of 1.5 inches high and need a 10 inch print , we will need to scan at a higher resolution than if we needed it the same size. You can see my basic rules of scanning photo restoration here.

When we know the size we need we can scan accordingly. However our output size and print quality can be governed by the quality of the original. These factors include grain, focus, sharpness, paper texture.

Step 2 – Grain

When the photo has been scanned we need to examine the grain. Grain is naturally occurring, random flecks in the chemical creation of a photo. If the grain is very large then enlarging the image will enlarge the grain. This can affect the quality of the reprint. Keeping the image within agreed acceptable size, so as not to compromise quality.

Step 3 – Focus

Checking the image is in focus can sometimes only be seen when the image is enlarged. After scanning we can check the image to see if the focus is ok. If the image is out of focus then any photograph enlarging should kept within an acceptable size for quality purposes.

Step 4 – Paper texture

Paper fibers can affect the quality of a photo enlargement

Paper fibers can affect the quality of a photo enlargement

Like grain, paper texture can affect the quality of an enlargement. Paper fibers in old papers are course and long and can easily soften the look of an image. When combined with the grain make the image harder to see. Once again we can agree the acceptable size of the final image.

Step 5 – Sharpness

In this case, sharpness is more a combination of little or no paper texture, little or no grain and good focus. If you the image has all these, we are good to go for our photograph enlarging.

The above assumes that the photo is a physical one, what if we have just a mobile image or a digital image.

Photo enlarging of digital images

Photo enlarging of digital images is possible but again there some factors to consider. These are:

  1. Noise
  2. File Compression
  3. Resolution
  4. Focus
  5. Sharpness
  6. Optics

Noise

Digital noise can be a result a result of low light digital photography and or  high ISO settings. if you add file compression into the mix this can add the noise issues. An image without noise can be enlarged more than an image with noise. Similar to grain on our physical photo.

File Compression

File compression a limiting factor in photograph enlarging

File compression a limiting factor in photograph enlarging

Quality settings on the camera often mean how much space the photo take up on the memory card. The more space the photo takes up is often used to define how much file compression is being used. Images with less file compression show less digital artifacts. These artifacts appear as collections of pixels, clumps of pixels or small areas of smeared pixels. Enlarging images with heavy file compression in not possible without the image looking broken up and poor quality.

Resolution

A higher resolution image is normally better than a lower resolution image. The more pixels we start with, the bigger the photo enlarging can go. This is not always the case. A high resolution with huge file compression is not always as good as a lower resolution image with no file compression.

Focus

As with our physical photo an out of focus digital photo cannot be enlarged very much as it will just end up being a bigger out of focus photo. Keeping it small limits our ability to see the image is out of focus.

Sharpness

Sharpness can be defined by an image being in focus, having low file compression, being in high resolution and having low noise. A combination of all these is a good recipe for enlargement.

Optics

Good optics normally adds to sharpness and less distortions at the edges of the image. Shoot an image with a £40 mobile phone and the odds are the optics will be poor compared to a £600 phone. Better still shoot one with a digital SLR with an expensive lens with fine optics.

Now we know the deciding factors that can limit how much we can enlarge a photo, we can make better decisions on doing so.

Perhaps it was not a simple as you thought?