颜色处理

Question

I have this task to interchange colors in an image.

Change Red to Blue Change Blue to Green and Change Green to Red

User will input an image, and the output will show an image w/ interchanged colors.

I was given a hint to convert RGB to HSI. But still... I don't get to how to do it. What steps should I do to make this task possible? Below is the formula for converting RGB to HSI Thanks. :)

Equations to Convert RGB Values to HSI Values Suppose R, G, and B are the red, green, and blue values of a color. The HSI intensity is given by the equation

I = (R + G + B)/3.

Now let m be the minimum value among R, G, and B. The HSI saturation value of a color is given by the equation

S = 1 - m/I    if I > 0, or
S = 0            if I = 0.

To convert a color's overall hue, H, to an angle measure, use the following equations:

H = cos-1[ (R - ½G - ½B)/√R² + G² + B² - RG - RB - GB ]            if G ≥ B, or
H = 360 - cos-1[ (R - ½G - ½B)/√R² + G² + B² - RG - RB - GB ]    if B > G,

where the inverse cosine output is in degrees.

Answer 1

由于颜色以度为单位且为圆形，因此应在色调中添加120度。

Answer 2

Add 1/3 of the maximum Hue value to the H channel of each pixel. If you are using an 8U depth, add 255/3, if you are using 32F depth, add 0.333 (but subtract 1 if it overflows past 1)

Answer 3

you could try the hsv color rappresentation :

http://en.wikipedia.org/wiki/HSL_and_HSV

you can find under "Hue and chroma" how to transform

there maximal G means value is between 1 and 3 maximal blue value is between 3 and 5 and maximal R value is between 5 and 6 or 0 and 1 ! at the end you multiply with 60 and you get a degree like value

Answer 4

The way you've worded it makes me think you are supposed to do the underlying calculations, but since you have mentioned opencv as a tag, I'll say that you can transform an image to HSV (same as HSI I believe) with one line using opencv:

cvCvtColor( src, hsvDestination, CV_BGR2HSV );

You can find more information here: http://docs.opencv.org/modules/imgproc/doc/miscellaneous_transformations.html

Answer 5

Here are the functions I wrote (and some comments describing a couple) that are used to map "light" (hard to see on white paper) colors to black. I call CheckSwapWhite for each color to be printed, but it could be called for each pixel. I don't have a formula for creating something in gray-scale, but I bet you could find that with a creative Google search.

//----------------------------------------------------------------------------
/*
   Colour Brightness Formula

   The following is the formula suggested by the World Wide Web
   Consortium (W3C) to determine the brightness of a colour.

   ((Red value X 299) + (Green value X 587) + (Blue value X 114)) / 1000

   The difference between the background brightness, and the
   foreground brightness should be greater than 125.
 */
//----------------------------------------------------------------------------

int ColorBrightness( COLORREF cr )
{
   return ((GetRValue(cr) * 299) +
           (GetGValue(cr) * 587) +
           (GetBValue(cr) * 114)) / 1000;
}

//----------------------------------------------------------------------------
/*
   Colour Difference Formula

   The following is the formula suggested by the W3C to determine
   the difference between two colours.

     (maximum (Red   value 1, Red   value 2) - minimum (Red   value 1, Red   value 2))
   + (maximum (Green value 1, Green value 2) - minimum (Green value 1, Green value 2))
   + (maximum (Blue  value 1, Blue  value 2) - minimum (Blue  value 1, Blue  value 2))

   The difference between the background colour and the foreground
   colour should be greater than 500.
 */
//----------------------------------------------------------------------------

int ColorDifference( COLORREF c1, COLORREF c2 )
{
   return (max(GetRValue(c1), GetRValue(c2)) - min(GetRValue(c1), GetRValue(c2)))
        + (max(GetGValue(c1), GetGValue(c2)) - min(GetGValue(c1), GetGValue(c2)))
        + (max(GetBValue(c1), GetBValue(c2)) - min(GetBValue(c1), GetBValue(c2)));
}

//----------------------------------------------------------------------------

COLOREF CheckSwapWhite( COLORREF cr )
{
   int      cdiff;
   int      bdiff;

   bdiff = 255 - ColorBrightness( cr ); // 255 = ColorBrightness(WHITE)
   cdiff = ColorDifference( cr, RGB(0xFF,0xFF,0xFF) );

   if( (cdiff < gnDiffColorThreshold) ||  // (500 by default)
       (bdiff < gnDiffBrightThreshold) )  // (125 by default)
   {
      return RGB(0x00,0x00,0x00); // black
   }
   return cr;
}

The two threshold variables are configurable settings with the given defaults.