You can choose whatever software for presenting ECG signal. I did the image by Matlab 2015a in Ubuntu 10.10.3/Debian 8.1. However, assume that you do not have here the original signal. You need to vector smartly to get nice output. I am interested how much different vector/visual techniques maintain the original signal. The thread To convert only black color to white in Matlab is about some tools to measure how much you lose signal from one technique. The optimum would use such methods that you could maintain the signal quality and return from the bigger image the smaller image.

Example picture

enter image description here

How can you scale this image for A3 or bigger for printing?

  • It is not understood the purpose of the re-scaling? Any photo program could interpolate the available pixels to a different resolution, a vector scaling program could attempt to do it better (they don't) using different methods. Most printers (driver) will scale the available pixels to print a smaller (or larger) image to using the whole page? If it was vectors then vectors are scalable before they are rasterised into a set of pixels. What is the need? and what are you trying to accompish beyond what interpolating it could do? – Psycogeek Jun 14 '15 at 9:17
  • Essential information missing: What software are you using? On which OS? What is your intent with the print? – Hannu Jun 14 '15 at 10:58
  • @Hannu I added the answer to your comment in the body of the question. Any more pieces of information needed? – Léo Léopold Hertz 준영 Jul 28 '15 at 11:48

Starting with the known:

  • The image given is 701px × 561px
  • A3 paper size is 16.25" x 11.75"

And the bit you may be missing which is that printed output needs a dot density running from around 150 dots per inch up to around 300 dots per inch. Anything much below 180-200 starts to become noticeably grainy, above 300 rarely results in noticeable improvements except in very fine lines.

So your image size would give an ideal print between around 4.7"x3.7" down to maybe 2.3"x1.9"

This tells us you need to find around 3x the number of pixels linearly.

The only way to do this is to use an image processing algorithm that interpolates between known pixels to fill in the gaps. Photoshop, The GIMP or other photo processing tools will have filters that will do this but the output might well be less than stellar since these are mainly aimed at processing photographs not line charts.

Another way to look at this issue though is to view the image on a large monitor - such as my 24" which is larger that A3 with a much lower dpi (around 90'ish) - then zoom the image so it fills the screen. If that image is usable for whatever purpose you have, then you don't need to worry - print one off and see how it looks!

  • How can you estimate how well your techniques can maintain the original signal/image? The best case would be that you can return from the processed image the old image. – Léo Léopold Hertz 준영 Jul 28 '15 at 11:49
  • Not sure I understand your question. If you are printing, the question is irrelevant since that will be the endpoint of your processing. If you are wanting the image scanned back in again, you need to update your original question as you haven't shared all the facts needed for a solution. The original q. implies you want a usable A3 print from limited pixels, my a. should help you work out if you can successfully do that in your situation - there is no hard and fast answer because it very much depends on the original and on the use the print is put too, how viewed, etc. – Julian Knight Jul 28 '15 at 20:55

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