Straightening Blueprints

[Jim Slade]

I have blueprints that have become warped in the scanning and microfilm process.

The blueprints have reference lines that should be vertical and horizontal but they are neither and they are not straight. 

Is there some kind of transformation where I can identify lines that should be horizontal and vertical and adjust the image with different amounts of rotation by area?

[thomaso]

There is no Affinity tool for automatic, partial image distortion. Without knowing your image I assume just rotation wouldn't correct a warped image. You could try the Mesh Warp Tool or the Shear Tool, possibly applied to selections (maybe feathered). – Or upload a sample image for more specific response.

[Jim Slade]

Here is an example. I have drawn some blue lines that make the correct spots for some of the grid. At you move to the top the image falls short of the grid lines. At the bottom, the image falls to the left of the grid lines. The towards the bottom left, they are shifted to the left.

[GarryP]

Mesh Warp, as mentioned by thomaso, might be able to do what you want, possibly with more than one pass – e.g. (1) Get the horizontals lined-up, (2) get the verticals lined-up, etc.

However, you may need a lot of time and experimentation to get something good.

Unfortunately, guides don’t work with the Mesh Warp functionality so a lot of manual movement and hand-to-eye coordination will be required.

You could practice by creating a grid out of some lines, then combining and rasterising them into a Pixel layer, and then using the Liquify Persona to bend things around a bit, then using Mesh Warp to try and get the original back. (Keep a copy of the original rasterised layer as a memory aid.)

[thomaso]

Even if you are able to reduce the distortion in the top right / bottom right corners of your sample image … I doubt it would be possible to correct all subtle distortion in the entire image by this way. Even in APhoto's Liquify Persona with its additional tools and options it appears quite time consuming and difficult to achieve the wanted geometrical perfection.

Thus (not only for perfection), it can be a lot faster to draw the plan grid as new objects (as you actually started already with your blue lines) + use only the text snippets as they are in the current image. (= without fixing text distortions)

If you use AD you could use a line stroke with black in its centre + white at its edges to "automatically" cover the existing, unwanted lines by your new drawing.

[NotMyFault]

One tedious way:

1. Paint helper lines on separate layer(s) above pixel layer
2. use mesh warp tool, on pixel layer
3. in destination mode, add nodes where the straight lines cross (double-click)
4. change to source mode
5. adjust nodes and handles so they line up with destination grid. This is very time-consuming, but the best available tool in Photo.

see older discussion