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Questions about Ortho Mosaic

Hi there

I am a student studying UAV images in Korea.

I have a question about image mosaic processing, so I have to write a question.

Due to the mismatch of the brightness values among the various images, the mismatch of the brightness values is confirmed even in the mosaic image.

I know there are regression methods and histogram matching methods for color(brightness) correction while looking at several papers. Can I find out which method Pix4D uses?

It is okay to give a brief description, not a detailed description.

Although it is a rude request, I hope you can help me with my research.
I look forward to your reply.
Thank you.

Pix4D uses a custom color alignment algorithm. This algorithm accounts for both exposure mismatches between images of a project (global offset and gain per image) and camera-related defects such as vignetting (that result in pixel-varying correction terms). While this problem can seem complex at first, we exploit the results of the geometric computations of step 1 (mandatory) and step 2 (when available) to make it tractable.

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Hi Emmanuel,

Is the color alignment algorithm a substitution for the regression methods and/or histogram matching that Seo Wonwoo mentioned? i.e.: would attempting to correct or normalize the brightness levels of photos BEFORE entering them into Pix4D be redundant?

Thanks!

Hi Patrick,

Pix4D does a global balancing, so correcting or normalizing the brightness level in beforehand would be redundant. In case you use images which are already more balanced or homogeneous (because you apply any type of previous color balancing) would not be bad, but as other software packages, Pix4D prefers to work with original images as otherwise, we cannot know which processes have been applied to the images and we have no control of the algorithms and transformations which happened before getting into Pix4D.

Regards.