CODEWITHSUNDEEP
iosobjective-cimage-processinggpuimage
Noé Malzieu
Noé Malzieu

Reputation: 2600

Automatic white balance in iOS Objective-C

I'm trying to fix the white balance of a picture on iOS. In my app, people can take a picture and get 2 things : an OCR and an "improved" version of the image.

To do the OCR, I improve the image with GPUImage (using GPUImageAdaptiveThresholdFilter). But that image is made only of black and white pixels. For my "improved" version, I want to have : - the right color balance (meaning my white is really white and not yellow when I take the picture inside) - good contrast.

I tried with GPUImageContrastFilter and GPUImageWhiteBalanceFilter. GPUImageWhiteBalanceFilter works well but GPUImageWhiteBalanceFilter takes parameters (like temperature) and that really depends on the image input.

So is there a way to "calculate" these parameters or are there objective c algorithms to fix white balance ? Either ready to use, or simple using GPUImage ?

Thanks !

Upvotes: 0

Views: 704

Answers (2)

Artal
Artal

Reputation: 9143

You can use CoreImage to auto enhance images. It will do the analysis for you.

This is done by acquiring a set of CIFilter with the necessary modifications that you can just apply to your image.

See more info here.

Upvotes: 1

Lou Franco
Lou Franco

Reputation: 89172

It may take time, but you can use your OCR function as a kind of scoring algorithm for a hill-climbing (or other) optimization algorithm.

  1. Take a portion of the image (to speed it up)
  2. Pick some parameters and improve the image
  3. Run it through OCR -- hopefully your OCR can give some confidence or you have some way of scoring the output (number of words?)
  4. Change the parameters -- use an optimization algorithm to decide how to do this.
  5. Go to 3 -- stop when you run out of time or it's good enough

If OCR is too slow -- you may have to pick something else to score with. Perhaps there's a way to compare your output images with known good ones and get a diff.

Upvotes: 0

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