How to convert DICOM from monochrome 1 to monochrome 2?

I am working on a project with DICOM images where I need to compare two DICOM images. The problem is that one is in monochrome 1 and the other is in monochrome 2 (zero means white and black respectively). How can I convert these pixel intensities in order to compare them? I am using the "pydicom" toolkit.

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Your main problem is not photometric interpretation (MONO1 / 2).

You cannot compare the pixel intensities of two DICOM images unless they are at the same scale (e.g. Hounsfield Units).

If you have

(0028,1052) RescaleIntercept - present with any value
(0028,1053) RescaleSlope - present with any value
(0028,1054) RescaleType - present with value "OD" or "HU"

      

Then it's pretty simple: apply a linear transformation:



<measured value> = <pixel value> * RescaleSlope + RescaleIntercept

      

The measured values ​​can be compared.

The same is true if you have a non-linear LUT modality stored as a lookup table in the header, but the same restrictions apply for the Rescale type.

Otherwise, I would refrain from comparing pixel values. Of course, it seems easy to just invert one of the two images, but the fact that they have different photometric interpretations tells me that they were acquired by different devices or methods. This means that the pixel data is visually correct and comparable, but not mathematically related.

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