Measuring shift between two images along one direction only

I have to measure shifts between two monochromatic images.

These images are actually spectra before calibration, which are very noisy and full of unwanted features, but they basically look like following

I know that between different images, they have shifts along x-direction, but not along y-direction. And I want to know the amount of the shift along x-direction between them.

Luckily I found a function in skimage, register_translation, which can be used for arbitrary subpixel precision. But the problem is, I want to know shift along x-direction only, and I want resulting y-direction shift to be 0, but the program finds the shift to x and y at the same time, presumably along the direction perpendicular to the features. (marked as blue arrow in the figure)

So, I am wondering :

1. is there any function or package in python that measures the shift between two images along one direction only, or even with any prior knowledge?

2. what is a correct way of finding shifts between two noisy images? Would finding maximum cross-correlation value in FFT space would do the job?

Some simple maths should do in this situation if register_translation gives you the xy shift, be it in vector or component form. You can calculate the movement in x that would be required if the y shift was non-existent, which is what you want. I am travelling so unfortunately can't give you the graph right now, would recommend drawing the triangles out.

The extra x shift required (x_extra) is defined by:

x_extra = y * tan[arctan(y_shift/x_shift)]

Which is simplified to:

x_extra = y_shift^2 / x_shift

Therefore, the total shift in x is:

x_shift_total = x_shift + x_extra

Where the x_shift is given to you by register_translation.

If you then move imageA by x_shift_total, it should be aligned with imageB, assuming the x_shift given by register_translation is correct.

@jni I would be keen to implement this as an option in register_translation!