Dreadnought
04-01-2011, 20:14
This thread is started from scraps of advice I have given in a number of posts throughout the forum. As scanning questions seem to come up quite often, I thought it may be useful to create a specific thread for tips and questions.
The Basics
Firstly, my advice to all forum members is to scan their photographs at a resolution of at least 300 dpi and save at the highest jpeg quality as possible whilst keeping below the file size limit. The smaller the original photograph, the higher resolution you can scan at the better. For slides and small photos of say two and a half inches square, it is preferable to scan in with resolutions up to 2400 dpi, or even higher, so that the resulting image is of good resolution at a reasonable size.
The maths is simple - a standard postcard (6x4 inches), scanned at 600 dpi will end up at 6 x 600 = 3600 pixels wide by 4 x 600 = 2400 pixels.
With black and white photos, I always scan as a 'colour document' (not 'colour photo' because descreening is normally on), obviously dependent upon particular scanner settings, in order to maintain tonal properties. Sepia tones very often add character. If these tones prove to be too heavy, you can always apply some desaturation or adjust the hue ... most photo editors have this facility.
Anything that is truly photographic, like a photographic print or a negative, should be scanned with descreening OFF.
Descreening is used to scan an image that has been screened, i.e printed with a pattern of dots. Printing presses are not capable of printing any shades of colour or grey, they are "faked" using a "halftone screen," which is a pattern of dots spaced close together. (Look at a newspaper with a magnifying glass and you'll see.)
So for anything printed on a printing press …. posters, newspapers, magazines, brochures, and anything like that, they should be scanned with descreening ON. Otherwise, you end up with the familiar pattern of dots all over the picture (called a moire pattern).
Scanners vary, and with some, if descreening is ON for a true photograph, you may not notice any difference, but with others, they limit the scanning resolution.
When it comes to postcards, the original printing of these varies enormously and you have to ascertain whether they are truly photographic cards, or printed on a press as just mentioned (the cheaper publishers). You can normally see this with a magnifying glass. That’s why sometimes you will get the dreaded dots on postcards, and sometimes not, and you think eh…? Haven’t changed anything?
If your scanner software also has the ‘Unsharp Mask’ option, this will make the picture sharper. However, if you turn on ‘Unsharp Masking’ with a screened image, the pattern of dots is sharper and more exaggerated ….. exactly the opposite of what descreening does!!
The Basics
Firstly, my advice to all forum members is to scan their photographs at a resolution of at least 300 dpi and save at the highest jpeg quality as possible whilst keeping below the file size limit. The smaller the original photograph, the higher resolution you can scan at the better. For slides and small photos of say two and a half inches square, it is preferable to scan in with resolutions up to 2400 dpi, or even higher, so that the resulting image is of good resolution at a reasonable size.
The maths is simple - a standard postcard (6x4 inches), scanned at 600 dpi will end up at 6 x 600 = 3600 pixels wide by 4 x 600 = 2400 pixels.
With black and white photos, I always scan as a 'colour document' (not 'colour photo' because descreening is normally on), obviously dependent upon particular scanner settings, in order to maintain tonal properties. Sepia tones very often add character. If these tones prove to be too heavy, you can always apply some desaturation or adjust the hue ... most photo editors have this facility.
Anything that is truly photographic, like a photographic print or a negative, should be scanned with descreening OFF.
Descreening is used to scan an image that has been screened, i.e printed with a pattern of dots. Printing presses are not capable of printing any shades of colour or grey, they are "faked" using a "halftone screen," which is a pattern of dots spaced close together. (Look at a newspaper with a magnifying glass and you'll see.)
So for anything printed on a printing press …. posters, newspapers, magazines, brochures, and anything like that, they should be scanned with descreening ON. Otherwise, you end up with the familiar pattern of dots all over the picture (called a moire pattern).
Scanners vary, and with some, if descreening is ON for a true photograph, you may not notice any difference, but with others, they limit the scanning resolution.
When it comes to postcards, the original printing of these varies enormously and you have to ascertain whether they are truly photographic cards, or printed on a press as just mentioned (the cheaper publishers). You can normally see this with a magnifying glass. That’s why sometimes you will get the dreaded dots on postcards, and sometimes not, and you think eh…? Haven’t changed anything?
If your scanner software also has the ‘Unsharp Mask’ option, this will make the picture sharper. However, if you turn on ‘Unsharp Masking’ with a screened image, the pattern of dots is sharper and more exaggerated ….. exactly the opposite of what descreening does!!