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When you want to reduce the physical size of a picture (width x height) there are two different ways to do it. Whichever way you prefer this concerns the size of the picture on the computer screen.

Use "Paint"

You can use "Paint" which is included in every Windows program. Go to "Start" --> "Programs" --> "Accessories" --> "Paint". When you then go to "File" --> "Open" you open a copy of your picture in the program. Because it's a copy, whatever you do to it, your original will not change as long as you save the new version of your picture under a new name.

When you want to save the new picture version always choose "Save as ...", because then you can change the picture file name and choose in which folder to save it. If you click on "Save", then most probably the original picture will be overwritten ( and lost to you ) or you don't know where the computer saved it.

When you change the picture size in "Paint" the procedure is different from most image editing programs.

Once you have opened your picture in "Paint" you go to "Image" --> "Stretch / Skew". This is the part where "Paint" is different from most picture editing programs. In most image editors the "aspect ratio" ( width divided by height ) is preserved, in other words the picture is changed symmetrically. In "Paint" it is not so.

When you change the size in "Paint" you are offered a choice of how many percent (%) to change width ( Horizontally ) and height ( Vertically ). The starting point is 100 %, which is unchanged size; with 50% you reduce the size down to 50% of the original.

So if you change only height to 50% it means the picture of your old slim and tall grandfather will turn the gentleman into a fat and short person. Because you changed only the height. To reduce the size symmetrically you have to use same percentage for both width and height.

As a result of reducing the physical size ( pixels x pixels ) also the picture file size will be reduced. Please note, the picture is not saved in your folder as a picture but as code. When you open the picture file the computer reads the code and produces the picture on the screen. With smaller physical size you get less picture code and therefore also a smaller file.

Use Image Editor

I use Irfanview for my own picture editing and changing needs. Basically all editors change the size in the same way, only the terms and words are little bit different. To change the physical size in an image editor go to "Image" --> "Image Size" or something similar - in Irfanview "Resize / Resample".

In most image editors the "aspect ratio" is preserved by default, but you can switch it off - don't do it. This means when you open the "Resize" window the numbers for "width" have an dark background - "highlighted". Now when you hit the "Return key" ( with an arrow to the left ) the highlighted numbers disappear. Instead you type in the new width that you want, usually this is in pixels by default, although in most programs you can change to inch or centimetres.

Once you have typed in the new width the program calculates the corresponding height and changes that. When you save the new version of your picture, remember to use "Save as ..." and either change the name completely or just add a letter or a number at the end - before the extension ( .gif, .jpg, .png, or whatever you want ). Never keep two different pictures with same name in different folders. One day may be the original is overwritten by mistake and lost forever.

As the physical size of the picture directly affects the file size so do the number of colours / colour shades too. If you try to explain a photo picture to a blind person - who knows what yellow, green, etc. means - you need a lot of words because of the many colours. The same goes for the picture file. The more details and colours there are in the picture the more code is needed to produce it.

What is EXIF data ?

EXIF means "Exchangable Image File Format" and is intended for storing information in image files in addition to pixel and colour information. Both digital cameras and camera phones have this property.

You can view the data, for instance in Windows XP by giving a right hand click on the file name in the folder where the picture is. Choose "Properties" --> click on "Summary" - sometimes continue with "Advanced". You can use this also to reduce picture file size.

For additional info about EXIF and other Operational Systems ( like Vista ) go to Exif data is your friend.