How can I reverse engineer a simple through-hole board?
Take the best pictures of both sides of the board that you can.
You can use a scanner to scan the bottom side of the board, but not all scanners will be able   to focus the top layer because of the height of the components.  

To this guide I used a 3MP camera of the iPhone 3GS without any special lighting or anything.    You will almost always likely to have a picture taken with better equipment and conditions.






Import then to a blank canvas on your favorite editing program. I'm using Adobe Fireworks,  you photoshop or almost any image editing software.
The images must be in separated layers.

Use the Polygon Lasso tool to crop the board from the rest of the picture. Do the same for the other side.

Use CMD-X to cut and then CMD-V to paste. It will lift the selection from the background. And then just delete the background. Do the same for the other side.

Use the Rotation CW/CCW and Flip Horizontal/Vertical to adjust the pictures to the correct position.


You will want the bottom of the board to be mirrored, so it matches the components side.




6.Decrease the opacity of the top layer down to around 50%~75% so we can se through it.


7.The 2 images are not in the same size, or angle. So we will use the Distortion tool to resize and straighten the corners of the top side so it match the bottom side.

 * Alignment is critical, so take your time, use the zoom/magnifier and check if everything is aligned. Look for the holes in the board, it is the easier way to check if the board is misaligned.

Blending

There are many methods that can be used to blend images.
Not all will work on all cases.

But I will go through a few of methods that may work for the majority of people.


The adjustments are subjective and will depend on your board color, illumination, exposure, etc... there are many variables, play around and find what values works best for you.


1. Screen Blend


Drag the bottom side to upwards the components side (copper side's layer on top of component side's layer).
Darken the copper layer using Brightness/Contrast filter and set brightness to -50
Select the copper layer and select blend mode to Screen/Interpolationor Average and set to 80





2. Luminosity Blend


Drag the bottom side to upwards the components side (copper side's layer on top of component side's layer).
Increase the constrast of the copper layer using Levels filter, drag the pins to twords the hill.

Select the copper layer and select blend mode to Luminosity and set to 50




Brush + Threshold


Drag the bottom side to upwards the components side (copper side's layer on top of component side's layer).
Select the copper layer and use the Brush and draw lines connecting the solder pads/holes, you can also use the path/line tool to draw straight lines instead. Use a solid color that is not used by the solder mask. In this case the solder mask is green/yellowish, so I used blue.

Apply a Invert filter.

Use the Levels filter or Threshold filter to extract just the solid color.
Drag the left pin all the way to the right.

Apply the filter Hue/Saturation and choose the color of the track of you preference rotating the Hue.

Select the copper layer and select blend mode to Additive and set the opacity to around 70 to adjust the intensity of the track.





Now we are ready to write down the values, and then transfer it to a CAD Software.