Digitised images usually require some adjustments before you can start the retouching process.
Sometimes fixes can be very simple – here we explain two of the most basic and effective processes you’re likely to need before you start retouching an image.
Resizing prints
While you can often copy prints at their original size and an appropriate resolution, virtually all of your scanned slides or negatives will need to be resized.
It’s usually wise to match the resolution to the end usage you have planned because if you enlarge the image after editing you risk making your adjustments obvious. Different usages have different resolution requirements, which we outlined in the previous chapter.
As explained, when originals are small (eg: 35mm film frames) and you want to make prints from them you should scan at much higher resolutions. If you’ve scanned a 36 x 24 mm film frame at 2400 ppi to make A4 sized prints it needs to be resized to fit on the paper.
While most printer drivers can adapt an image file to fit onto a specified sheet of paper, it’s better to resize before printing using the settings in your favourite image editor. This gives you a lot more control over the process and enables you to produce several versions of the image, each with its size and resolution matched to a different destination; one for emails, another for printing and another for including in a slideshow that will be viewed on a TV screen, for example.
Resizing is provided in even the most basic editors and it’s very easy to accomplish. As an example we’ve chosen a 35mm slide taken in Athens in the 1960s and scanned at 2400 dpi. Resizing will make this image usable for printing or sharing online.
The first stage in resizing is to select the Image > Size functions in the editor and change the Resolution from 2400 pixels/Inch to 300 Pixels/Inch, which is the ideal resolution for printing. Leave the Resample box unchecked so the image keeps its original size.
If you want to print the image, the one we’ve selected will fit nicely onto an A4 sheet of photo paper, although it’s too large for a snapshot-sized print. To downsize it to around 15 x 10 cm, it’s best to use the settings in the editor, which will reduce the chance of moiré, fringing and other artefacts, rather than leaving it to the printer.
The same dialog box is used for resampling images when you want to downsample (reduce) or upsample (enlarge) the image. For either operation, make sure the width and height parameters are linked before you check the Resample box to change the image parameters. Watch out for haloes around sharp edges, which indicate over-sharpening, especially in images that are upsampled.
Downsampling (top) and upsampling (below) adjustments. Choose the Bicubic Sharper method for downsampling and the Smoother or Preserve Details resampling method for upsampling.
When resampling images for printing the resolution can be reduced gradually for prints larger than A3 size because we view them from greater distances. Don’t be tempted to go below about 200 ppi as it will risk the image becoming pixellated.
When resizing pictures for emailing, posting on social media and/or viewing on a computer or TV monitor, create copies of your original files with separate file names. Take account of the native resolution of the screen itself; if you want the image to fill the screen when it is opened, aim to match the screen’s resolution.
Cropping
Many digitised images will require at least some cropping and you’ll save time if this task is carried out before you embark on any further adjustments. A common reason to crop scanned images is to straighten tilted horizons, a frequent occurrence when photos were taken with cameras that lacked any compositional aids. Most software provides special straightening settings to make this process quick and easy.
Most editors provide straightening tools (circled in red in this screen grab of Affinity Photo’s workspace). To straighten the photo, simply draw a line along a path in the image that you want to be horizontal or vertical; the software will rotate the image and crop it as shown in the lower picture.
Another popular reason to crop is to remove areas that are either irrelevant to the picture or too badly damaged to justify spending time trying to fix them. You can also crop to improve the composition of pictures, obtain a different aspect ratio to fit an image into a frame or onto a page or sheet of printing paper, or change a horizontal image into a vertical one, or vice versa.
Another example of a straightening tool, this time from ACDSee Photo Studio. The same software is shown in the lower screen grab, with the cropping tool used to remove a large area of detail-free sky containing many blemishes.
While rectangular pictures tend to look better when posted on websites that have set boundaries, another reason to crop is to change the rectangular shape of the original to a circle or an oval. This is surprisingly easy, as shown below.
These illustrations show how to crop a messy, hand-cut vignetted original. Step 1: use the round selection tool to select the area you want to keep. Step 2: Click on Select > Inverse to change the selection to the area you want to crop away. Step 3: Cut away the unwanted area. Step 4: The final vignetted image.
Precautions when cropping
1. Cropping should not be permanent. Always work on a copy of the image you plan to crop and use a non-destructive editor.
2. Because pixels are discarded, cropping will always reduce overall resolution. You need to be sure beforehand just how much you can afford to lose.
3. Any inherent problems in the image, such as noise or unsharpness, will be magnified by enlarging the image after cropping.
4. When cropping to a specific aspect ratio, your crop should be compliant with standard print sizes, particularly if somebody else will be doing the printing.
Useful links:
This article by Margaret Brown is an excerpt from Photo Restoration pocket guide
Pocket guide Partner: Camera House
