12-lead ECG library - FAQ

How do you get your scans to look so good?

We use a simple scanner and simple software. The problem with most scanners is that they come with sophisticated software that adds enhancement and other refinements to the scan without your knowledge. We scan in 2 colours at 300 dpi. From a colour original (i.e. black on pink) this usually separates tracing from grid easily.

On darker originals we scan in 256 colours, split the image into red, green and blue channels and keep only the red which can be transformed into 2 colours containing the ECG trace and no grid. The pink grid is very red and hence is turned white by this technique; conversely black is very un-red and remains black. Alternatively, if you have a computer with plenty of memory, you can scan in 24 bit colour and remove all the colours other than black from the palette.

Scanning a monochrome photocopy or a very dark original produces a very messy scan with bits of grid all over the place. We have developed our own filters for graphics packages and been experimenting with Fast Fourier Transforms to help remove the 'noise'. We have had some success with this but a lot more work is needed. We are considering scanning at 600 dpi but this would need a lot more computing power than we have. A 6000 x 4000 matrix would take a very long time to compute.

How do you get the ECG into the webpage form?

The ECG images are initially scanned at 300 dpi. The image is then reduced to 76.5 dpi and compressed using the GIF 89a format. The background colour white is made transparent so that the grid can show through. The grid is simply defined as a webpage background and each small square is 3 pixels across. This explains why the ECG is reduced in size to fit the screen. On a standard ECG tracing the small squares are 1mm x 1mm. At 300 dpi 1 mm is roughly equal to 12 pixels hence the need to reduce the size by a factor of 4. (Ideally the scans should be reduced to 76.2 dpi but that is not practical).

How can I use the ECG images offline?

Please feel free to use the images in the ECG library for teaching or personal study. If you would like to print the image on paper remember to increase its size by 400% for it to be the original size. The image will become grainy at this resolution but it should still be of educational value.

Are the ECGs in this library the same as those in your book?

No. The ECGs in the book are more comprehensive, consisting of 80 of the commonest abnormalities. They are also described in more detail with labelling of features. We had many surplus recordings and thought we would share them.

Where can I find your book?

It is called 'ECGs by example' published 1997 by Churchill Livingstone (ISBN 0 443 056978) and should be available worldwide in all good (medical) bookshops.

Do you have raw digital data from ECG machines?

No. The files are scanned images of the paper output of ECG machines and does not contain enough detail for modern research into computer ECG analysis. Such databases do exist. Look at the list of related links.

[ECG library homepage] [About the library and its librarians]
[related links] [History of ECGs]