## Shift hue of an RGB Color

I'm trying to write a function to shift the hue of an RGB color. Specifically I'm using it in an iOS app, but the math is universal.

The graph below shows how the R, G, and B values change with respect to the hue.

Looking at that it seems like it should be a relatively simple to write a function to shift the hue without doing any nasty conversions to a different color format which would introduce more error (which could be an issue if continue applying small shifts to a color), and I suspect would be more computationally expensive.

Here is what I have so far which sort of works. It works perfectly if you're shifting from pure yellow or cyan or magenta but otherwise it gets a little squiffy in some places.

Color4f ShiftHue(Color4f c, float d) { if (d==0) { return c; } while (d<0) { d+=1; } d *= 3; float original[] = {c.red, c.green, c.blue}; float returned[] = {c.red, c.green, c.blue}; // big shifts for (int i=0; i<3; i++) { returned[i] = original[(i+((int) d))%3]; } d -= (float) ((int) d); original[0] = returned[0]; original[1] = returned[1]; original[2] = returned[2]; float lower = MIN(MIN(c.red, c.green), c.blue); float upper = MAX(MAX(c.red, c.green), c.blue); float spread = upper - lower; float shift = spread * d * 2; // little shift for (int i = 0; i < 3; ++i) { // if middle value if (original[(i+2)%3]==upper && original[(i+1)%3]==lower) { returned[i] -= shift; if (returned[i]<lower) { returned[(i+1)%3] += lower - returned[i]; returned[i]=lower; } else if (returned[i]>upper) { returned[(i+2)%3] -= returned[i] - upper; returned[i]=upper; } break; } } return Color4fMake(returned[0], returned[1], returned[2], c.alpha); }

I know you can do this with UIColors and shift the hue with something like this:

CGFloat hue; CGFloat sat; CGFloat bri; [[UIColor colorWithRed:parent.color.red green:parent.color.green blue:parent.color.blue alpha:1] getHue:&hue saturation:&sat brightness:&bri alpha:nil]; hue -= .03; if (hue<0) { hue+=1; } UIColor *tempColor = [UIColor colorWithHue:hue saturation:sat brightness:bri alpha:1]; const float* components= CGColorGetComponents(tempColor.CGColor); color = Color4fMake(components[0], components[1], components[2], 1);

but I'm not crazy about that as It only works in iOS 5, and between allocating a number of color objects and converting from RGB to HSB and then back it seems pretty overkill.

I might end up using a lookup table or pre-calculate the colors in my application, but I'm really curious if there's a way to make my code work. Thanks!

**Edit** per comment changed "are all" to "can be linearly approximated by".
**Edit 2** adding offsets.

Essentially, the steps you want are

RBG->HSV->Update hue->RGB

Since these *can be approximated by* linear matrix transforms (i.e. they are associative), you can perform it in a single step without any nasty conversion or loss of precision. You just multiple the transform matrices with each other, and use that to transform your colors.

There's a quick step by step here http://beesbuzz.biz/code/hsv_color_transforms.php

Here's the C++ code (With the saturation and value transforms removed):

Color TransformH( const Color &in, // color to transform float H ) { float U = cos(H*M_PI/180); float W = sin(H*M_PI/180); Color ret; ret.r = (.299+.701*U+.168*W)*in.r + (.587-.587*U+.330*W)*in.g + (.114-.114*U-.497*W)*in.b; ret.g = (.299-.299*U-.328*W)*in.r + (.587+.413*U+.035*W)*in.g + (.114-.114*U+.292*W)*in.b; ret.b = (.299-.3*U+1.25*W)*in.r + (.587-.588*U-1.05*W)*in.g + (.114+.886*U-.203*W)*in.b; return ret; }

**Shift hue of a color online,** Shift hue of a color online. In Colors | Keywords | Thanks to Keywords: shift, hue , color, adjust, change, modify, spin, color wheel� I'm trying to write a function to shift the hue of an RGB color. Specifically I'm using it in an iOS app, but the math is universal. The graph below shows how the R, G, and B values change with respect to the hue.

The RGB color space describes a cube. It is possible to rotate this cube around the diagonal axis from (0,0,0) to (255,255,255) to effect a change of hue. Note that some of the results will lie outside of the 0 to 255 range and will need to be clipped.

I finally got a chance to code this algorithm. It's in Python but it should be easy to translate to the language of your choice. The formula for 3D rotation came from http://en.wikipedia.org/wiki/Rotation_matrix#Rotation_matrix_from_axis_and_angle

**Edit:** If you saw the code I posted previously, please ignore it. I was so anxious to find a formula for the rotation that I converted a matrix-based solution into a formula, not realizing that the matrix was the best form all along. I've still simplified the calculation of the matrix using the constant sqrt(1/3) for axis unit vector values, but this is much closer in spirit to the reference and simpler in the per-pixel calculation `apply`

as well.

from math import sqrt,cos,sin,radians def clamp(v): if v < 0: return 0 if v > 255: return 255 return int(v + 0.5) class RGBRotate(object): def __init__(self): self.matrix = [[1,0,0],[0,1,0],[0,0,1]] def set_hue_rotation(self, degrees): cosA = cos(radians(degrees)) sinA = sin(radians(degrees)) self.matrix[0][0] = cosA + (1.0 - cosA) / 3.0 self.matrix[0][1] = 1./3. * (1.0 - cosA) - sqrt(1./3.) * sinA self.matrix[0][2] = 1./3. * (1.0 - cosA) + sqrt(1./3.) * sinA self.matrix[1][0] = 1./3. * (1.0 - cosA) + sqrt(1./3.) * sinA self.matrix[1][1] = cosA + 1./3.*(1.0 - cosA) self.matrix[1][2] = 1./3. * (1.0 - cosA) - sqrt(1./3.) * sinA self.matrix[2][0] = 1./3. * (1.0 - cosA) - sqrt(1./3.) * sinA self.matrix[2][1] = 1./3. * (1.0 - cosA) + sqrt(1./3.) * sinA self.matrix[2][2] = cosA + 1./3. * (1.0 - cosA) def apply(self, r, g, b): rx = r * self.matrix[0][0] + g * self.matrix[0][1] + b * self.matrix[0][2] gx = r * self.matrix[1][0] + g * self.matrix[1][1] + b * self.matrix[1][2] bx = r * self.matrix[2][0] + g * self.matrix[2][1] + b * self.matrix[2][2] return clamp(rx), clamp(gx), clamp(bx)

Here are some results from the above:

You can find a different implementation of the same idea at http://www.graficaobscura.com/matrix/index.html

**Hue, Value, Saturation,** Hue is also a term which describes a dimension of color we readily They are produced as secondary colors when RGB light hues are mixed, as follows:. SHIFT HUE OF A COLOR ONLINE. RGB-HSV-HSL-Spinned color #000000 (0 , 0 , 0) Hex #000000: RGB-HSV-HSL-Custom Color Palette Site Color Palette Color Palette About Us

I was disappointed by most answers I found here, some were flawed and basically flat-out wrong. I ended up spending 3+ hours trying to figure this out. The answer by Mark Ransom is correct, but I want to offer a complete C solution that's also verified with MATLAB. I have tested this thoroughly, and here is the C code:

#include <math.h> typedef unsigned char BYTE; //define an "integer" that only stores 0-255 value typedef struct _CRGB //Define a struct to store the 3 color values { BYTE r; BYTE g; BYTE b; }CRGB; BYTE clamp(float v) //define a function to bound and round the input float value to 0-255 { if (v < 0) return 0; if (v > 255) return 255; return (BYTE)v; } CRGB TransformH(const CRGB &in, const float fHue) { CRGB out; const float cosA = cos(fHue*3.14159265f/180); //convert degrees to radians const float sinA = sin(fHue*3.14159265f/180); //convert degrees to radians //calculate the rotation matrix, only depends on Hue float matrix[3][3] = {{cosA + (1.0f - cosA) / 3.0f, 1.0f/3.0f * (1.0f - cosA) - sqrtf(1.0f/3.0f) * sinA, 1.0f/3.0f * (1.0f - cosA) + sqrtf(1.0f/3.0f) * sinA}, {1.0f/3.0f * (1.0f - cosA) + sqrtf(1.0f/3.0f) * sinA, cosA + 1.0f/3.0f*(1.0f - cosA), 1.0f/3.0f * (1.0f - cosA) - sqrtf(1.0f/3.0f) * sinA}, {1.0f/3.0f * (1.0f - cosA) - sqrtf(1.0f/3.0f) * sinA, 1.0f/3.0f * (1.0f - cosA) + sqrtf(1.0f/3.0f) * sinA, cosA + 1.0f/3.0f * (1.0f - cosA)}}; //Use the rotation matrix to convert the RGB directly out.r = clamp(in.r*matrix[0][0] + in.g*matrix[0][1] + in.b*matrix[0][2]); out.g = clamp(in.r*matrix[1][0] + in.g*matrix[1][1] + in.b*matrix[1][2]); out.b = clamp(in.r*matrix[2][0] + in.g*matrix[2][1] + in.b*matrix[2][2]); return out; }

**NOTE: The rotation matrix only depends on the Hue** (`fHue`

), so once you've computed `matrix[3][3]`

, you can **reuse** it for every pixel in the image that is undergoing the same hue transformation! This will improve the efficiency drastically.
Here is a MATLAB code that verifies the results:

function out = TransformH(r,g,b,H) cosA = cos(H * pi/180); sinA = sin(H * pi/180); matrix = [cosA + (1-cosA)/3, 1/3 * (1 - cosA) - sqrt(1/3) * sinA, 1/3 * (1 - cosA) + sqrt(1/3) * sinA; 1/3 * (1 - cosA) + sqrt(1/3) * sinA, cosA + 1/3*(1 - cosA), 1/3 * (1 - cosA) - sqrt(1/3) * sinA; 1/3 * (1 - cosA) - sqrt(1/3) * sinA, 1/3 * (1 - cosA) + sqrt(1/3) * sinA, cosA + 1/3 * (1 - cosA)]; in = [r, g, b]'; out = round(matrix*in); end

Here is a sample input/output that was reproduceable by both codes:

TransformH(86,52,30,210) ans = 36 43 88

So the input RGB of `[86,52,30]`

was converted to `[36,43,88]`

using a hue of `210`

.

**Hue,** Change color of: Background. Button The RGB (Red, Green, Blue) color model is the most known, and the most used every day. It defines a color The HSB model is also known as HSV (Hue, Saturation, Value) model. The HSV model was� Darken color Change color saturation Greyscale/desaturate a color Invert a color Random color generator Blend colors Gradient generator Shift hue of a color Triad color scheme Tetrad color scheme Complementary color Split complementary colors Analogous color scheme

Basically there are two options:

- Convert RGB -> HSV, change hue, convert HSV -> RGB
- Change the hue directly with a linear transformation

I'm not really sure about how to implement 2, but basically you'll have to create a transformation matrix and filter the image through this matrix. However, this will re-color the image instead of changing only the hue. If this is ok for you, then this could be an option but if not a conversion cannot be avoided.

**Edit**

A little research shows this, which confirms my thoughts. To summarize: The conversion from RGB to HSV should be preferred, if an exact result is desired. Modifying the original RGB image by a linear transform also leads to a result but this rather tints the image. The difference is explained as follows: The conversion from RGB to HSV is non-linear, whereas the transform is linear.

**HSL and HSV,** RGB to HSV (or HSB) color code converter and conversion formula. or. Enter red color (R):. Enter green color (G):. Enter blue color (B):. Hue (H):, �. Saturation ( S): The R,G,B values are divided by 255 to change the range from 0..255 to 0.. 1:. The RGB color space describes a cube. It is possible to rotate this cube around the diagonal axis from (0,0,0) to (255,255,255) to effect a change of hue. Note that some of the results will lie outside of the 0 to 255 range and will need to be clipped. I finally got a chance to code this algorithm.

The post is old, and the original poster was looking for ios code - however, I was sent here via a search for visual basic code, so for all those like me, I converted Mark's code to a vb .net module:

Public Module HueAndTry Public Function ClampIt(ByVal v As Double) As Integer Return CInt(Math.Max(0F, Math.Min(v + 0.5, 255.0F))) End Function Public Function DegreesToRadians(ByVal degrees As Double) As Double Return degrees * Math.PI / 180 End Function Public Function RadiansToDegrees(ByVal radians As Double) As Double Return radians * 180 / Math.PI End Function Public Sub HueConvert(ByRef rgb() As Integer, ByVal degrees As Double) Dim selfMatrix(,) As Double = {{1, 0, 0}, {0, 1, 0}, {0, 0, 1}} Dim cosA As Double = Math.Cos(DegreesToRadians(degrees)) Dim sinA As Double = Math.Sin(DegreesToRadians(degrees)) Dim sqrtOneThirdTimesSin As Double = Math.Sqrt(1.0 / 3.0) * sinA Dim oneThirdTimesOneSubCos As Double = 1.0 / 3.0 * (1.0 - cosA) selfMatrix(0, 0) = cosA + (1.0 - cosA) / 3.0 selfMatrix(0, 1) = oneThirdTimesOneSubCos - sqrtOneThirdTimesSin selfMatrix(0, 2) = oneThirdTimesOneSubCos + sqrtOneThirdTimesSin selfMatrix(1, 0) = selfMatrix(0, 2) selfMatrix(1, 1) = cosA + oneThirdTimesOneSubCos selfMatrix(1, 2) = selfMatrix(0, 1) selfMatrix(2, 0) = selfMatrix(0, 1) selfMatrix(2, 1) = selfMatrix(0, 2) selfMatrix(2, 2) = cosA + oneThirdTimesOneSubCos Dim rx As Double = rgb(0) * selfMatrix(0, 0) + rgb(1) * selfMatrix(0, 1) + rgb(2) * selfMatrix(0, 2) Dim gx As Double = rgb(0) * selfMatrix(1, 0) + rgb(1) * selfMatrix(1, 1) + rgb(2) * selfMatrix(1, 2) Dim bx As Double = rgb(0) * selfMatrix(2, 0) + rgb(1) * selfMatrix(2, 1) + rgb(2) * selfMatrix(2, 2) rgb(0) = ClampIt(rx) rgb(1) = ClampIt(gx) rgb(2) = ClampIt(bx) End Sub End Module

I put common terms into (long) variables, but otherwise it's a straightforward conversion - worked fine for my needs.

By the way, I tried to leave Mark an upvote for his excellent code, but I didn't have enough votes myself to allow it to be visible (Hint, Hint).

**Colorizer,** RGB to HSL color space converter and conversion formula. The R,G,B values are divided by 255 to change the range from 0..255 to 0..1: Hue calculation:. 2. Change the Hue value to that of the Hue opposite (e.g., if your Hue is 50°, the opposite one will be at 230° on the wheel — 180° further around). 3. Leave the Saturation and Lightness values as they were. 4. Convert this new HSL value back to your original colour notation (RGB or whatever).

**RGB to HSV conversion,** This MATLAB function converts the red, green, and blue values of an RGB image to hue, saturation, and value (HSV) values of an HSV image. No Special skills are required to shift hue of image using this tool. Just drop image in tool, then enter hue value using slider and click shift hue button to modify hue of image. Tool will shift the hue of uploaded image and display the preview along with download button.

**RGB to HSL converter,** While it's helpful to denote how much of each colour exists, it is not a very friendly system to describe a hue shift, saturation, or value/brightness)� Adjust hue Sharpen image Special filters Adjust channels Vignette effect Colorize image Merge images Crop image Resize image Image color picker Get colors from image Blur image Tilt-shift effect Emboss effect Color emboss effect

**Convert RGB colors to HSV - MATLAB rgb2hsv,** increases, which is known as blue shift in an optical cavity. The angular color shifts of RGB primary colors can be clearly explained by blue shift. However, the primary colors usually only account for a small portion of the displayed images. The majority are those colors created by mixing RGB colors with different ratios.