Ramblings of a Grouch

In the previous article we looked at saving image files for archiving or printing. This week we will see what needs to be done to produce a file which can be emailed to others. Don't forget - a CD from DigitalMemoriesonline can include files suitable for all purposes.

The first thing we can do is to save the file in a different format. There are two types of file I use for serious images work, known as 'TIF' and 'JPEG'. You choose the one you want when you save the file in Photoshop, Paint Shop Pro or whichever program you are using.

A TIF file is called 'lossless' - every piece of information in the image is saved exactly as it is on the screen. This is the type of file to use for producing prints and for archiving. It retains the best quality image at the expense of the largest filesize. A JPEG file, on the other hand, is a 'lossy' format. The information in the image is compressed to take up a smaller space by, for example, marking an area of sky as a certain shade of blue rather than saving the same information for every individual pixel. Saving as a JPEG file can reduce the file size by 70% or more, but at the expense of quality.

So it would seem that we need a JPEG file to keep the filesize down for emailing. But how much quality do we need to sacrifice? The answer is that we can reduce the quality of an image by a substantial amount if we just need to view it on screen.

To display an image on a computer monitor we only need to set the resolution to 72 PPI. Any greater resolution makes no discernible difference. Why is this? Well, get right up close to your monitor (remove your spectacles if you wear them else you will go cross-eyed) and look at the image. You can actually see the individual pixels, and if you count them (not recommended) there will be 72 across each inch of the screen. So saving at 72 PPI matches what your screen can display.

At first glance it may seem that the file will be around a quarter of the starting size (300 divided by 72) but, remembering that we need to figure out the number of pixels across and down, we can see that the filesize is actually one sixteenth of the original - a very handy saving. Applying certain tweaks when saving as a JPEG, I was able to get my original photograph down to 864 Kilobytes and still have a very acceptable image on screen.

Check out the part of the photo saved in this manner (the 300 DPI image from last week is shown first for comparison). I think you will agree that the JPEG is perfectly acceptable for viewing (without endangering the knitted socks from Aunt Flo next Xmas).

300 dpi, filesize 16Kb

72 dpi, filesize 3.3Kb

So there we are - 300 PPI TIF for saving, 72 PPI JPEG for sending. And that is exactly the format in which DigitalMemoriesonline will supply your finished images should you choose to purchase a CD of the finished restoration.

(And that handsome young man in the centre of the picture is my father. Obviously some things are not inherited ...)

Until next time ...

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