What is the function of white in RGBW? - colors

I have not been able to find much info on the RGBW color system, other than that the final W stands for 'white'. I thought you could form white perfectly well with just red, green and blue, so I do not understand the function of white here.
Searching StackOverflow, I've found this question about converting between RGB and RGBW. Both answers suggest this 'algorithm' for conversion:
// RGBW from RGB
R, G, B, W = R, G, B, min(R, G, B) // i.e. W=min(R,G,B)
// RGB from RGBW
R, G, B = R, G, B // throw away the W
This doesn't only look useless, it's also not true. My Android phone, running Cyanogenmod, has a light sensor that outputs RGBW (cat /sys/class/sensors/light_sensor/lux) and the white value is definitely not min(r,g,b). I've made a chart with the values:
(The X axis is time.)
The black line represents the white value (an actually white line would be rather difficult to see), the other colors are accurate (i.e. red line is the measured red value, etc.). From sight, I cannot determine any relation between white and the other colors, so it probably serves a function. I just cannot understand which.
It's this sensor: http://www.capellamicro.com.tw/EN/product_c.php?id=68&mode=16
And here is the source code that controls the sensor: https://github.com/mozilla-b2g/kernel-android-galaxy-s2-ics/blob/master/drivers/sensor/cm36651.c#L605-L630
That is all I've been able to figure out, but nothing contains info on what this white value represents.

That exactly it – you can't form white perfectly using only RGB LEDs. This is because the RGB colorspace is a small, pale fraction of the CIE-1931 XYZ space, and it’s distorted: incrementing an RGB values’ “R” by 1 is not at all qualitatively the same as incrementing its “G” value or “B” value, for example.
Just do a side by side comparison and the difference will be very, very clear. You can google “True white RGB led” and you'll learn a lot more; a good introduction is here: http://www.ledsmagazine.com/articles/print/volume-10/issue-6/features/understand-rgb-led-mixing-ratios-to-realize-optimal-color-in-signs-and-displays-magazine.html

Related

wordcloud2 drops long words, which gets the colors mismatched

so i have a dynamic list of text that i want to visualize in a wordcloud. sometimes some of the words are too long and they get dropped from the display. i can scale down the size of everything, but it's not always clear what scale i should get down to in order to prevent things from being dropped. i'd rather not fiddle with this and just accept some things are dropped. also, everything is in a shiny app and i have a slider to control scale if really needed. the problem though is i want my text colored by properties of the words in my dataset. in this example below you can see how each "word" has a color associated with it...
wc <- data.frame(
word = c("too big to fit this one is","red","green","blue"),
freq = c(2,1,2,3),
col = c("black","red","green","blue"),
stringsAsFactors = FALSE
)
>wc
word freq col
1 too big to fit this one is 2 black
2 red 1 red
3 green 2 green
4 blue 3 blue
wordcloud2(wc, color = wc$col)
this then draws the wordcloud but the first element is dropped and the colors don't drop too ("red" is colored black, "green" is colored red, and "blue" is colored green). i can't do wordcloud2(wc, color = col) like an aes style call in ggplot, the wordcloud does draw but all the text is clear... i can hover over it but not see any of it. anyone else work through this issue? thanks!!!

How to find out 70% mid blue (#686e9f)

My company launched a new branding. I'm creating palettes to rework on numerous websites. One of the colors is named Mid blue (#686E9F) and an associated color is Mid Blue Tint as 70% Mid blue but no RGB/Hex values.
How to find out 70% mid blue (#686e9f)?
Reference:
In fact you can find it by using the opacity.
Your blue "tint" is the same as your #686e9f wich means this rgba representation rgba(104,110,159). And with 0.70 opacity on this you get back your color.
to test you can paste this rgba(104,110,159,0.7) on this website :
http://www.menucool.com/rgba-color-picker
So you could begin to translate the hex-number into RGB values
-> https://www.rgbtohex.net/hextorgb/
Then I presume you could multiply those values with 0.7, if I understand this 70% stuff correctly.
If I understood your question correctly and you were asking for a RGB representation:
rgb(104, 110, 159)
68 -> 104
6e -> 110
9f -> 159
The hex value is just a RGB value in hexadecimal. IF you were looking for something else, please specify a clear question.

Non-normalized colour-conversion Yxy colour space

I'm doing a psychology experiment involving colour.
Before I start my analysis I have to convert three colours in Yxy colour space into CIELAB. I used a colour spectrometer gun, but my luminances in Yxy space are non-normalized (in 1000s, up to infinity.) I need to get them to be either normalized luminances between 1-100 so I can use the converters I have found.
If anyone can help me with either normalizing my L values, or fully converting my Yxy values into CIELAB that'd be great!
My means in (Y, x, y) are:
Peach: (1218.333, 0.362, 0.341)
Yellow: (2105, 0.393, 0.424)
Grue: (340.333, 0.262, 0.357)

Office Open XML satMod results in more than 100% saturation

I'm trying to calculate the satMod (saturation modulation) for something like the following:
<a:srgbClr val="58CAFF">
<a:satMod="300000"/>
</a:srgbClr>
Section 20.1.2.3.27 of the EMCA-376 spec says of the <satMod> element: "This element specifies the input color with its saturation modulated by the given percentage. A 50% saturation modulate reduces the saturation by half. A 200% saturation modulate doubles the saturation."
The problem I'm having is that many colors are already saturated enough that increasing the saturation by 300% (the 300000 in there corresponds to 300%) puts it way out of the 0-100% range. I have been simply capping the saturation at 100% but my results are pretty different from what Excel does.
It seems there is some special magic happening here in cases where the saturation should overflow. Anyone know what Office/Excel does in this case?
I found essentially the same question here: http://social.msdn.microsoft.com/Forums/en-US/oxmlsdk/thread/040e0a1f-dbfe-4ce5-826b-38b4b6f6d3f7
The answer indicated that the srgb color should be converted to linear rgb first and then to hsl before the saturation is modified. For me that hasn't solved the problem.
That was me that asked that original question. I have since figured it out. With ever single color transformations (satMod, redMod, lumMod, etc.), you have to clamp the value to within sRGB 0,0,0 or 255,255,255 (or 1.0,1.0,1.0). Meaning if your satMod modifies your color by 300% and the result is a color value above 255, clamp it to 255 (or 1.0). With that resulting color, you can then apply other color transforms if they are in your color srgbClr or other color spaces.
This is what I do in an example like yours.
Convert color to HSL space (these kinds of RGB->HSL routines are common on Bing/Google in a look up).
Send in that color and the satMod to a routine like this:
Public Sub modulateHSL(ByVal c As HSL, ByVal val As System.Double)
Select Case c
Case HSL.Hue
Hue = Hue * val
If Hue = 0.0 Then
If val >= 1.0 Then
Hue = val - Fix(val)
End If
Else
Hue = Hue - Fix(Hue)
End If
Case HSL.Saturation
Saturation = Saturation * val
Case HSL.Luminance
Luminance = Luminance * val
End Select
HSL_To_sRGB(Hue, Saturation, Luminance)
Clamp_sARGB()
End Sub
At the end of this routine, you'll notice two calls 1) HSL_To_sRGB(Hue, Saturation, Luminance) and 2) Clamp_sARGB(). The first one converts back to sRGB space and the second one clamps the RGB values, like this:
Public Sub Clamp_sARGB()
If Red <= 0.0 Then Red = 0.0 Else If Red >= 1.0 Then Red = 1.0
If Green <= 0.0 Then Green = 0.0 Else If Green >= 1.0 Then Green = 1.0
If Blue <= 0.0 Then Blue = 0.0 Else If Blue >= 1.0 Then Blue = 1.0
If Alpha <= 0.0 Then Alpha = 0.0 Else If Alpha >= 1.0 Then Alpha = 1.0
sRGB_To_HSL(Red, Green, Blue)
End Sub
Note there is no need to use Linear RGB in the case where you're only modifying the saturation. I maintain both RBG and HSL spaces in class level fields (RGB in 0-1 space), so that's why you see sRGB_To_HSL(Red, Green, Blue) at the end of that routine.
Now this is for DrawingML as it appears in PowerPoint. Excel may be different (there is a long drawn out thread here that deals with charts that may also have your answer). Keep in mind that modifying saturation can also modify luminance depending on how you coded your routine. If that's the case, you'll want to use the original luminance when converting back from HSL to RGB.
If none of this is working for you, can you put an example XLSX on a
DropBox point somewhere with what is going on, what you're expecting, etc.?

Alpha blending a red, blue, and green image to produce an image tinted to any rgb value?

Basically, I have a context where I can't programatically tint an image, though I can change it's alpha value. With some experimentation, I've found that I can layer a red, blue, and green version of the image, with specific alpha values, to produce a wide range of colors. However, I am wondering if it's possible to achieve a true RGB representation through this method? If so, what is the formula for converting an RGB value into different alpha values for the red, blue, and green layers.
The basic "equation" of alpha combination is:
alpha * (R1,G1,B1) + (1-alpha) * (R2,G2,B2)
When you have three layers with alpha you are actually combining 4 layers (the 4th one is black) so the final color is:
alpha1 * (R1,G1,B1) + (1-alpha1) * (
alpha2 * (R2,G2,B2) + (1-alpha2) * (
alpha3 * (R3,G3,B3) + (1-alpha2) * (0,0,0) ) )
Provided you have the same image on each layer and layer1 is the red channel (G1=B1=0) and layer2 is green and layer3 is blue you get:
(alpha1 * R, (1-alpha1)*alpha2 * G, (1-alpha1)*(1-alpha2)*alpha3 * B)
For a white pixel you can do any possible color. For a black pixel you cannot do anything but black. For any other pixel, you are restricted by the values of R, G and B.
Say you wanted to achieve (Rd, Gd, Bd) at a pixel where the current color is (R, G, B) then you would have to choose:
alpha1 = Rd/R
alpha2 = Gd/(G*(1-alpha1))
alpha3 = Bd/(B*(1-alpha1)*(1-alpha2))
The problem is that alpha can typically only be between 0 and 1. So, for example, if Rd > R there is nothing you can do.
You can do better if you can control the blending function (for example, in Photoshop).
I don't think that's possible, if I understand you correctly.
If, for a certain pixel, your image's red value is, say, 0.5, you can combine that with an alpha in the (typical) range [0,1] to form any value up to and including 0.5, but you can't go above, to get e.g. 0.6 or so as the output value.
If you're looking to create 3 layers that blended together add up to the original image, it's quite possible. Here's a link to a Python script that calls functions in Paint Shop Pro to do the hard parts.
http://pixelnook.home.comcast.net/~pixelnook/SplitToRGB.htm
If you need more detail than that, leave a comment and I'll try to fill it in later.

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