how to convert color lines to black and white solid and dashed lines?

[frankiem]

Does anybody know of a way to convert an image of a graph with 3 colored lines (red, green and blue on a white background with black X and Y axes) into a black and white graph with solid, dashed and dotted lines? I only have a .png image of these graphs as I lost the raw data in a recent hard disk crash. The image does not have separate layers. This is to publish a paper in an academic journal which does not do color.

I am using Windows but I can also get access to Ubuntu (i.e. if what I want can be done in Gimp - however I am not familiar with Gimp, so please spell out the required steps if this can be done in Gimp).

Alternatively, does anybody know of a programme which could convert my red, green and blue curves into 3 series of data points? I could then draw the black and white patterned lines I want.

Thanks

 

[ChrisHirst]

Create a new layer, above the current layer, name it and switch to it.

Select the path tool (looks like a fountain pen nib)

Trace the curve you want with the 'pen', the closer the path nodes are together the more accurate your trace will be.

Set the 'background' layer hidden, so only the layer with your new path is visible.

Set the foreground colour you want your new curve to be.

Edit -> Stroke Path .. set the width, solid colour and choose the line style you want (lots of dashes and dot syles to pick from)

Click the [ Stroke ] button.

Hide your new layer, Show the 'background@ layer

Repeat for the other curves, saving after each step.

Once all three are done, show all your "curve" layers, then use File -> Export ... to save to whatever format you want the image to be in. If you have got the paths right your original curves in the background layer png will be hidden below your drawings.



Chris.

Indifference will be the downfall of mankind, but who cares?
Time flies like an arrow, however, fruit flies like a banana.
Webmaster Forum

 

[frankiem]

Brilliant. Thanks.