CODEWITHSUNDEEP
javaimageimage-processinggraphicsnormalization
P basak
P basak

Reputation: 5004

How to normalize RGB value with reference RGB values

I want to get RGB values of an image in many lighting conditions. To get a somehow neutral scenario, I want to normalize the RGB values with RGB values of some predefined images.

Let me explain. I have 6 predefined images and I know their exact average RGB values. Now I will take the picture of the unknown image in different lighting conditions. I will also take the pictures of predefined 6 images in same conditions. Now my goal is to define a normalization formula by comparing the known reference rgb values of the predefined images to the values computed from the camera picture. with this normalization parameter I will calibrate the RGB value of the unknown picture. So that I can get average RGB value from the unknown picture in a neutral manner irrespective of the lighting condition.

How can I achieve this easily in Java.

Upvotes: 6

Views: 8942

Answers (2)

trumpetlicks
trumpetlicks

Reputation: 7065

Is the reason you are doing this to truly normalize RGB, or are you trying to normalize the images to have similar brightness. Because if your goal is simply the brightness, then I would convert to a color standard that has a brightness component, and normalize only the brightness component.

From there you can take the new image in the different color component standard and convert back to RGB if you like.

The steps (but not in java):

1) Convert - RGBImage --> YUVImage
2) Normalize RGBImage using the Y component
3) Convert - Normalized(YUVImage) --> Normalized(RGBImage)

In this way you can implement Normalization on the brightness using the algorithm described here.

ELSE, you can average the averages for each channel and use those as the numerator for the normalization factors for your new images calculating each channel separately.

Upvotes: 1

Mark Ransom
Mark Ransom

Reputation: 308140

For differing lighting situations, a linear RGB correction is all that is required. Simply multiply each of the R,G,B values by a constant derived for each channel.

If there was only one reference color, it would be easy - multiply by the reference color, and divide by the captured color. For example if your reference color was (240,200,120) but your image measured (250,190,150) - you would multiply red by 240/250, green by 200/190, and blue by 120/150. Use the same constants for every pixel in the image.

With multiple colors to match you'll have to average the correction factors to arrive at a single set of constants. Greater weighting needs to be given to the brighter colors, for example if you had a reference of (200,150,20) and it measured (190,140,10) you'd be trying to double the amount of blue which could be very far off. The simplest method would be to sum all the reference values and divide by the sum of the measured values.

Upvotes: 0

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