Understanding digital images
and image restoration

Converting a photograph to a digital image

A photograph is converted to a digital image using a scanner.
The scanner divides the photograph into very small squares, called pixels.
Each pixel is a single colour

Note:
For colour images, each pixel could be one of 16 million colours.
For black & white, each pixel could be one of only 256 shades of grey.

A small identity card photo of 25.4mm sq (1 inch sq) could be divided into 360000 pixels. In this case, the scanner would be set to 600dpi
(600x600 = 360000)

Examples (black & white are easier to see):

photo

16x16 pixels

256 squares (pixels)

photo

32x32 pixels

1024 pixels

photo

64x64 pixels

4096 pixels

photo

128x128 pixels

16384 pixels

photo

256x256

65536 pixels

photo

512x512 pixels

262144 pixels

The above images in context

 

photo

"Caving"

Image cropped & re-sized to 600x270 pixels (162000px) ie. This image is smaller than the 512x512 example!

Restoring the image

The objective of restoration, is to modify the image, in order to make it look like the photograph, at the time it was taken (or to try to get it as close as possible, within realistic time constraints).

Study Example

We will be working on an area of 1.5% (that being the 512x512 image) of the above context photograph, at its original scanned resolution.

Note: At this degree of zoom, there are no sharp focussed edges. In fact this is typical of old photographs that have decayed.

The example is extreme - for general photo resoration, with this particular image, we would not need to work at this level, as the image faults cannot be seen, when viewed at normal sizes.
However, it is good to show how an image can be restored to the finest degree.

Photographs degrade over time

A photograph is the result of a chemical reaction, that takes place on the surface of the photographic paper.

This chemical reaction is stopped, when the photograph is produced... but the final chemicals (that make up the photograph) are often not stable.
Over the years, they change... colours, fade, disappear, or a haze can appear over the entire photograph.

When we scan the photograph, the image has all these faults...
(The above example 128x128 shows these faults)

Image restoration

Remember: The image is just a collection of pixels, each with it's own colour, or shade of grey... to the computer, each colour is just a number.
'totally white' = 255   'totally black' = 0

In principal, therefore, we can simply change the numbers, to make the dark areas a bit blacker, and the light areas a bit lighter.

However... many faults leave light coloured spots.
By darkening the dark pixels, and lightening the light pixels, the faults can become more pronounced.

To solve this... We design a search for light coloured groups of pixels that are surrounded by dark pixels.
Once identified the lighter pixels are converted to the colours that surround them (removing the blemish).

Below is an example of this in action:

Look closely at the 2nd image: It is covered in small white marks, that are no longer present in the third image.

photo

Original Image

Dull grey.

photo

Lighter & Darker

Better, but with faults.

photo

Faults Removed

Most of them - the rest will be removed by hand.

Restoring the image by hand

In many cases, the blemishes that exist simply cannot be seen when the image is viewed at normal size.
However, for some old photographs these faults are highly visible at normal viewing sizes.
Additionally, when restored to this degree, the image is much better... so for this example, all the remaining faults will be removed.

This involves identifying a fault and zooming in to pixel level.
The pixels displaying the wrong colour, are reprogrammed to match the surrounding colours.
 

Click the image below, to compare the original image to the restored image.

Look closely - the first image is covered in blemishes, and is a dull grey..... the restored image is as perfect as needs be.

 

Focus on different areas and click the image

Restoration for general photographs

Almost anything is possible, however, for general restoration works, the primary objective, is to make the photograph presentable.
Typically, 'lightening & darkening', and perhaps sharpening the focus, is usually all that is required.

This general restoration is carried out on all the scanned photographs.

In depth restoration tends to be reserved for the more important photographs that deserve additional attention.

 

 

Part 3. Image Modification

 

Services & Tariffs