How do you make a nice fade from white to black with a limited set of colors?
I'm writing a "demo" for virtual machine i have designed and written. It has 4096 colors and i need to do a nice fade from white to black. Since there is only 16 different levels of gray i would like to extend this by using some more colors.
I have seen nice fades from white to black on the c64 using far fewer colors.
Is there any general function for doing this in arbitrary color spaces.?
You could calculate the brightness of the available colors:
RGB: brightness = (R + G + B) / 3
Or use other color models (HSL, HSV etc.): http://en.wikipedia.org/wiki/HSV_color_space#Lightness
and order the colors by brightness.
If you are free to generate any color, create/generate a nice palette of colors and, again, order by brightness.
Related
I am trying to figure out how to achieve a smooth transition between two colors.
I.E. this image is taken from Wikipedia.
When I try to do the same using my code (C++), first idea that came to mind is using the HSV color space, but the annoying in-between colors show-up.
What is the good way to achieve this ?
This is going to sound weird, maybe... but vertex shaders will do this nicely. If that's a quad (two tris) then place one colour on the left 2 vertices, and the other on the right, and it should blend across nicely.
Caveat: Assumes you're using some kind of OpenGL.
The only part of your question I feel I can answer is that you must somehow be transitioning through too many values in the H part of HSV.
H is for hue (different colors, like the rainbow effect in your gradient). In this case, it looks to me like you are only merging 2 different hues.
S is for saturation (strength of color from highly saturated to
gray)
L is for lightness (more or less luminosity (from your
color to its most white)
This is caused by a lack of color in between, as black (or grey in your case) = desaturated. It is like putting two transparent fade images together, there is a see through area in the middle as 2 50% transparencies don't equal 100% solid color.
To avoid this, I'd suggest placing one color above the other and fading that to transparent. That way there is a solid color base with the transition above.
I dont know what your using to display (DirectX, Windows display or whatever ) but try just having two images, one solid color and a single color with a fade from solid to transparent infront. That might work.
Assume that I've a gray image, and I want to draw e.g. text on it. Now the image has some dark and some bright regions. So if I choose for every character a separate color, in what way do I compute such a color to gain highest contrast of the text?
A pragmatic approach is to use yellow. (I don't know why, but its often used for subtitles in movies and documentaries)
Furthermore I could darken the yellow in regions of bright background, and highlight it in regions of dark background. But this may provide some layer-effects.
I know that the color space may be important. I start with an RGB gray value, but LAB, HSV, or HSL may be better suited to compute the optimal color.
EDIT:
As there was the question for a useful use-case: I really do not want to paint letters of text in different color. It is about color choosing for particular glyphs on gray textured background. (E.g. an MR image.)
The simplest answer to your question is to maximize the distance between the background and your text color.
If you convert to HSL, you can do this by maximizing the distance between L (V in HSV). And all that requires is to select white when the background lightness is less than 50% and black otherwise. Here is an example: http://jsfiddle.net/E2kU4/
if(bgLightness < 50){
color = "white";
}else{
color = "black";
}
I think that pretty much solves it, but on to a few other points:
I'm not sure what the use case is for this. A word with different colored characters might look really bad. Typically, subtitles select a single color for consistency.
Yellow does stand out against a black and white image because of its saturation. Furthermore (and I'm not sure how to put this into words exactly), yellow has a really high chroma compared to other colors with similar lightness. It is best demonstrated on the HUSL page; by the way, HUSL is a great library for creating readable colors.
Yellow easily contrasts with dark colors because it is very light. It doesn't contrast with light colors as well, but that is usually solved by adding a shadow/outline in subtitles. Another example: http://jsfiddle.net/E2kU4/1/
But you can apply the same technique (of applying a shadow or outline) to the black/white example for maximum contrast. Now, the outline has the maximal contrast against the text. The outline stands out from the background too, unless those colors are similar, in which case the contrast is already extremely high (e.g. Near black background, black outline, white text) http://jsfiddle.net/E2kU4/2/
Lastly, converting to and from HSL/RGB should be trivial. There are plenty of libraries to do it.
Could someone tell me why colors with a same rgb value (for example 127, 127, 127) look the exactly same in an image using sRGB space and one using CIE RGB space? Since one is non-linear (with gamma correction) and the other one is linear (without gamma correction), I think they should look kinda different. But image I've created looks exactly the same (I used Photoshop to create the former and for the latter, I tried Photoshop, OpenGL and OpenCV).
The difference is coming when you are manipulating an image or a color (changing the brightness or the saturation of an image). This is most visible when lowering the saturation of yellow. Try it in Photoshop with RGB and with Lab mode. Do not switch to grayscale mode, because it is using luminance correction, but the saturation slider in the Adjustment>Hue/Saturation menu.
You can also see the difference when playing with my color picker (just scroll down to the full-blown example), which represents colors in the CIE Lch space (it is using CIE Lab in the background).
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Seeing as how the three primary colors are cyan, magenta and yellow (CMY), why do monitors and almost all the GUI components out there use red, green and blue (RGB)? (If I'm not mistaken, printers use the CMYK model.)
Is there a historical, hardware/software, or other reason for it?
There's a difference between additive colors (http://en.wikipedia.org/wiki/Additive_color) and subtractive colors (http://en.wikipedia.org/wiki/Subtractive_color).
With additive colors, the more you add, the brighter the colors become. This is because they are emitting light. This is why the day light is (more or less) white, since the Sun is emitting in almost all the visible wavelength spectrum.
On the other hand, with subtractive colors the more colors you mix, the darker the resulting color. This is because they are reflecting light. This is also why the black colors get hotter quickly, because it absorbs (almost) all light energy and reflects (almost) none.
Specifically to your question, it depends what medium you are working on. Traditionally, additive colors (RGB) are used because the canon for computer graphics was the computer monitor, and since it's emitting light, it makes sense to use the same structure for the graphic card (the colors are shown without conversions). However, if you are used to graphic arts and press, subtractive color model is used (CMYK). In programs such as Photoshop, you can choose to work in CMYK space although it doesn't matter what color model you use: the primary colors of one group are the secondary colors of the second one and viceversa.
P.D.: my father worked at graphic arts, this is why i know this... :-P
The difference lies in whether mixing colours results in LIGHTER or DARKER colours. When mixing light, the result is a lighter colour, so mixing red light and blue light becomes a lighter pink. When mixing paint (or ink), red and blue become a darker purple. Mixing paint results in DARKER colours, whereas mixing light results in LIGHTER colours.
Therefore for paint the primary colours are Red Yellow Blue (or Cyan Magenta Yellow) as you stated. Yet for light the primary colours are Red Green Blue. It is (virtually) impossible to mix Red Green Blue paint into Yellow paint, or mixing Red Yellow Blue light into Green light.
The basic colours are RGB not RYB. Yes most of the softwares use the traditional RGB which can be used to mix together to form any other color i.e. RGB are the fundamental colours (as defined in Physics & Chemistry texts).
The printer user CMYK (cyan, magenta, yellow, and black) coloring as said by #jcomeau_ictx.
You can view the following article to know about RGB vs CMYK: RGB Vs CMYK
A bit more information from the extract about them:
Red, Green, and Blue are "additive
colors". If we combine red, green and
blue light you will get white light.
This is the principal behind the T.V.
set in your living room and the
monitor you are staring at now.
Additive color, or RGB mode, is
optimized for display on computer
monitors and peripherals, most notably
scanning devices.
Cyan, Magenta and Yellow are
"subtractive colors". If we print
cyan, magenta and yellow inks on white
paper, they absorb the light shining
on the page. Since our eyes receive no
reflected light from the paper, we
perceive black... in a perfect world!
The printing world operates in
subtractive color, or CMYK mode.
the 3 additive colors are in fact red, green, and blue. printers use cmyk (cyan, magenta, yellow, and black).
and as http://en.wikipedia.org/wiki/Additive_color explains: if you use RYB as your primary colors, how do you make green? since yellow is made from equal amounts of red and green.
This is nothing to do with hardware nor software. Simply that RGB are the 3 primary colours which can be combined in various ways to produce every other colour. It is more about the human convention/perception of colours which carried over.
You may find this article interesting.
How can I convert a grayscale value (0-255) to an RGB value/representation?
It is for using in an SVG image, which doesn't seem to come with a grayscale support, only RGB...
Note: this is not RGB -> grayscale, which is already answered in another question, e.g. Converting RGB to grayscale/intensity)
The quick and dirty approach is to repeat the grayscale intensity for each component of RGB. So, if you have grayscale 120, it translates to RGB (120, 120, 120).
This is quick and dirty because the effective luminance you get depends on the actual luminance of the R, G and B subpixels of the device that you're using.
If you have the greyscale value in the range 0..255 and want to produce a new value in the form 0x00RRGGBB, then a quick way to do this is:
int rgb = grey * 0x00010101;
or equivalent in your chosen language.
Conversion of a grayscale to RGB is simple. Simply use R = G = B = gray value. The basic idea is that color (as viewed on a monitor in terms of RGB) is an additive system.
http://en.wikipedia.org/wiki/Additive_color
Thus adding red to green yields yellow. Add in some blue to that mix in equal amounts, and you get a neutral color. Full on [red, green, blue] = [255 255 255] yields white. [0,0,0] yields monitor black. Intermediate values, when R=G=B are all equal will yield nominally neutral colors of the given level of gray.
A minor problem is depending on how you view the color, it may not be perfectly neutral. This will depend on how your monitor (or printer) is calibrated. There are interesting depths of color science we could go into from this point. I'll stop here.
Grey-scale means that all values have the same intensity. Set all channels (in RGB) equal to the the grey value and you will have the an RGB black and white image.
Woudln't setting R,G,and B to the same value (the greyscale value) for each pixel get you a correct shade of gray?
You may also take a look at my solution Faster assembly optimized way to convert RGB8 image to RGB32 image. Gray channel is simply repeated in all other channels.
The purpose was to find the fasted possible solution for conversion using x86/SSE.