Scanning

A major factor in image file sizes - is your scanner resolution setting.   The resolution setting in dpi (dots per inch - same as pixels per inch) - makes an immense difference.

e.g. if a given image scanned at 100 dpi results in a file size of 1 MByte.  Scanning this same image with a setting of 300 dpi would result in a file size of of 9 MBytes. So you can see that this setting is very important.

The choice a suitable setting - depends on why you are scanning a particular image. But whatever its for - there is no point in using resolution setting greater than the optical resolution of your scanner. Typically 150 or 300 or even 600 dpi - depending on your particular scanner.

If you are scanning an image for output to a printer - then there is nothing to be gained in exceed the resolution setting of your printer - typically 150 or 300 dpi.  However there is one exception to this - which is scanning small images that will be stretched (enlarged) before printing. In this case a higher resolution may be used.  e.g. If you are going double the dimensions of the original - then you should double the scanner resolution setting - but without exceeding its maximum optical resolution.

If the scanned image will only ever be viewed on a computer screen without further enlargement - then a maximum resolution of 75 to 100 dpi will be ample.

If you are scanning for archives then you should consider scanning at the maximum optical resolution of your scanner - and archived media such as recordable CD's.  It should be remembered that bright light causes degradation of old photographs and the least number of times they are scanned - the longer they will last.   Therefore - scanning at the highest resolution will provide some degree of future proofing - as resolutions of both printers and displays are improving all the time.

Another type of image is text scanned for input to Optical Character Recognition (OCR).  In this case - recognition accuracy increases with resolution and a minimum of 200 dpi should be used. Generally file size is not a problem when using OCR as the scanned image file can be deleted once it has been translated into real text.

Quality Considerations

Scanned images  take up a lot of storage space so they are usually compressed to save space.  The most two common formats being JPG and GIF.  If the images are only required for internet use then these are reasonable formats to use for the final image.   However there is a problem with these and many other image compression formats.  This is that they lose data - degrade the image.   This generally is only a problem if you intend to re-edit the image - because every time you reload and edit an image it is degraded a bit more.

The GIF format data losses (image degradation) is due to the reduction to 256 colours - apart from this loss due to colour reduction - gif compression is without data loss. Unfortunately 256 colours are generally insufficient for colour photographs - unless the original did not have a very wide range of colours and shades. 

The GIF format must be used when some parts of the image are to be transparent - as in the Good Connexions logo at the top of this page.  In grey scale mode It is adequate for B & W photographs.

The JPG format looses detail and is best suited when there are large areas of the same or a graduated colour.

There is one exception to JPG data losses -  there is no loss when the compression is set to one.   There is still a high degree of compression - and most graphics programs have the option to adjust  the compression setting from the Save or Save As.. Window.  But you do need to remember to return it to a higher setting for normal use.

You can maintain the quality of the original scan - by storing images in one of the bit-map type formats.  If you have scanned some really old valued family photographs for posterity then you want them to be as close to the original as possible.  Even if you intend enhancing them - removing blemishes - cloning missing corners etc. - you should keep a copy of the original scan and work on separate copies. 

When working on images - your screen should be set for at least 16 bit colour.  There is usually some interaction between the screen resolution (desktop area) and number of permitted colours - and you may find that need to reduce the screen resolution to 800 x 600 pixels or lower - depending on your Graphics Card Adapter.  Whilst it is possible to work at lower colour setting - you will not be able see so much detail as the intermediate colours are achieved by dithering.   You will not permanently lose colours when working with lower colour palettes - just the ability to work in fine detail. 

 

Image File Compression Without Loss

Graphics programs display and manipulate images in a bit-map type format - and images stored in this format retain the quality of the original  image without loss.  It doesn't mean that you precious disk space need be overwhelmed by a few images.  One answer is zipping - there isn't much difference in file sizes of a zipped bit-map compared with JPG and GIF file sizes.  In fact if a batch of BMP are zipped together often require less memory for storage overall - when compared with similar number of JPG and GIF files.

When saving pictures for inclusion in Family History there is the TIF format If supported by your graphics program.   TIF has a number of compression options - including the no loss LZW also used by WinZip.

A newer no loss format defined to replace the patented GIF format is PNG (Portable Network Graphics) format in web pages.  Supported by Netscape Communicator 4.0 & Internet Explorer 4.0 and onwards.  If you are getting new software for image editing & manipulation then you should ensure that it supports PNG.  The problem about using them on websites now - is the large number of people using older browsers not being able to view them.

If you are only compressing files for archive purpose only - then you may consider using a proprietary format used by your editing program - but remember that you will only be able to view your images using this program. Thus restricting your choice should you want change to a different product.

Size Does Count

When reducing images for inclusion in Family History records.  Make a copy of the original and reduce and crop that to the required final size.  DO NOT use the the constraining capability of your FH program other than for small adjustments - otherwise you will be including a file that could be up to 10 times bigger than it need be. This is of particular importane for images to be included with web-pages

The two GIF files below show how the amount of data space required to store a given image depends on how its size is controlled.

To the left is a copy of the image reduced to half size before saving.  This image has a file size of 7,378 bytes and is displayed actual size

To the right is the original image and has a file size of 24,572 bytes - constrained to half actual height and width.