Restoration is the process of attempting to wind-back the ravages of time on a photograph.
Types of damage that photos (positives) and/or film (negatives) may incur include:
- Chemical staining due to oil, solvents, impurities in development chemicals, physical proximity to other materials, water, condensation, oxidization, etc.
- Loss of contrast
- Sticking to other surfaces
Most of these types of damage can be repaired to some extent, usually by digitizing the photo or negative (if it's not already digitized) and then using image editing software such as the Darktable or the GIMP (both free and open source software), Lightroom or Photoshop (both commercial products from Adobe) or similar software packages.
Some of the strategies or general approaches that may be taken to restoration include the following.
Cloning is the act of duplicating the subject, color, texture or other visual properties from one part of an image to another. In restoration, this is usually used to mask out damaged areas such as dust, folding, staining or scratches.
Obfuscation is the act of reducing the apparent visual presence or impact of part of an image. This may be achieved, for instance, by reducing its contrast, lightening or darkening it, or changing its color to a more neutral tone.
Faded images may often be significantly enhanced by restoring their original contrast, or even digitally enhancing contrast beyond what was probably originally there. This process is generally very easy to achieve with photo manipulation software, either through a dedicated image contrast function (generally preserving the existing color balance of the image) or through finer grained control over individual color channels such as red, green and blue.
Cropping or outright removing parts of an image is sometimes the fastest and cheapest way to restore an image to a higher apparent overall quality, and can be particularly useful if significant damage has occurred at the edges or corners of an image, for example through a bent or dog-eared corner. Unfortunately, it is not always possible since it relies upon no other significant elements within the image being similarly close to the cropped-away edge. For example, in a portrait it is generally unacceptable to cut away part of the subject's head.