The importance of the scanning resolution
The concept of resolution is an integral part of scanning. It means the number of pixels along a certain unit of length (if this concept is unknown to you, revise the reading for the Student’s digital skills). Using the correct resolution is important for your scanned images to be a reasonable size for further processing.
The following series of images shows how the resolution affects the image quality. The sample image has been scanned with two different resolutions, 72 and 300 dots per inch (dpi), and then partial enlargements have been made of the images:
When scanning images, set the resolution with the original size as well as what it will be used for in mind:
- Size of original: if the original is very small (e.g. like a stamp) it often makes sense to choose a fairly high resolution (such as 600 dpi or more). if the original is very large (like a A4 paper) it is usually better to select a lower resolution (such as 72-150 dpi). This way, the scanned image will have enough detail but the image file will not be too large.
- Purpose: if you are going to view the image on-screen or e.g. publish it on the web, it is better to use a low resolution when scanning it. But if you want to print the image and all its details, select a higher resolution. A very high resolution is usually required of pictures to be published in newspapers and other printed products. Always remember to take into account both the original and the purpose of the image.
The higher resolution you scan your image with, the more pixels the final image consists of. Because higher resolution images also take up more space, scanning large images on high resolutions requires a lot from your computer’s processor and memory. If you use a too high scanning resolution, you may encounter computer performance issues due to the large size of the image. Thus, it is a good idea to set the scanning resolution at a suitable level already before scanning images.
You can scan any photo, newspaper clip, advertisment, poster, drawing, etc. Whatever it is you’re scanning, you need to always remember that copyrights limit their use: acquaint yourself with copyrights before going online with your pictures.
Before scanning images, also make sure you have the following things sorted out:
- Set the image orientation: you can rotate the image later on with editing software, but it’s wiser to set it the right way already on the scanner plate.
- Make sure you have the right settings: if another user has altered e.g. brightness or contrast values, your images may be ruined already at this point. You’ll make your job a whole lot easier later on, if you ensure that your scanning settings are correct beforehand: at least make sure the brightness and contrast levels are set to default in the program you use for scanning.
- Check your scanning resolution: the effect of the scanning resolution on everything that is done afterwards is huge. If you don’t yet know what the image will be used for, scan it with a fairly high resolution. That way you’ll make sure you can use it for e.g. poster printing in the future.
- Eliminate any reflections: for instance, the paper that newspapers are printed on is so thin that anything in the background will probably be visible in the scanned image. You can solve this problem by setting a piece of black paper or cardboard behind the object to be scanned. This way the scanner’s own light won’t throw any reflections or render the image translucent, rendering a better result.
- Use suitable color settings: you should use different scan settings when scanning a colored object than you would with a grayscale or black and white image. The chart below gives you a basic idea of the most common color settings (the settings and how they’re named may vary according to scanner).
|Image to be scanned
||Recommended color settings
|Color image||Truecolor tai 24 bit color|
|Grayscale photo or black and white drawing||Grayscale|
Scanning images works largely the same way irrespective of the type of flatbed scanner you might be using. In order to use one you need to have a scanning program installed on your computer: most operating systems have one preinstalled.
Quick instructions for scanning:
- Once you have powered the scanner, lift its lid and set the picture on the glass facing down. Then close the lid.
- Start your image processing software of choice, and in its menu, click File, Import and Twain Acquire (the manner and menu items may vary).
- Mark the scannable area with the program’s selection tool (see picture below).
- Set the desired scanning resolution (200 dpi in the picture below).
- Once you’ve gone through your scanning settings, click the program’s scan button. When the scanning process is complete, the finished image will appear in the image processing program. Please note that the image shown in the scanning program is a mere preview image and not the final, scanned image.
- Close the scanning program and save your scanned picture in the image editing program.
- Don’t forget your picture in the scanner! 🙂
Changing the resolution afterwards
When bringing a scanned image into e.g. a desktop publishing program, the size of the image in the program depends on the resolution it was saved in. If the resolution is not correct, the picture could take over the whole page (see image on the left below): this often happens, when an old photo (e.g. 72 dpi) is brought to a publishing program. When the resolution is suitable (e.g. 300 dpi), the picture will most probably shown the way you want it to be seen on screen (see image on the right below).
You can often change the resolution of an image in most image processing programs. Always remember, however, that changing the resolution of an image after scanning is not the same as defining the resolution when scanning! Altering the resolution upon scanning increases or decreases the amount of information to be “read” from the image, whereas changing the resolution in an image processing program defines how large (in pixels per inch) the image will be processed in e.g. publishing programs and on screen. Therefore, altering the resolution of an image after scanning does not enhance or worsen the quality of an image.
You can check the resolution in an image you open by clicking Image -> Image information in your image processing program. The example below shows the resolution of the picture to be 72 pixels per inch:
You can change the resolution by clicking Image -> Resize and setting a new resolution for your picture in the next window (see picture below). When you’ve set your new resolution, finish by clicking OK.