I am confused with how does MyPaint blend color, here are what I did:
It has a background layer (initial white color).
Select a brush with some color and alpha < 1, paint some lines on the canvas.
When I paint at the same line, it will be deepen.
Change the background layer to any color or image, the line still look nice.
So, my questions are:
How does it blend color when I paint at the same place with alpha < 1?
How does it blend color between canvas and background layer?
Thanks.
Related
I draw to a texture with a fragment shader in opengl.
I set my color to 100% red and 50% opacity, but when i then read this color i discover that it is no longer 100% red.
The same can be noticed with gimp.
I choose 100% red color but draw it with 50% opacity, when i then use the color picker tool, it tells me the red color is only 80%.
Is there a way to preserve the color value in opengl es 2.0?
The color is modified by the Bending function and operation. You have to disable blending.
There is no opacity, there is just an alpha channel. The alpha channel and the blend function define how a source color is mixed (blended) with the color in the target buffer. Hence if blending is enabled, then the final color is equal to the source color. If blending is disabled, the the color and the alpha channel are copied to the target without manipulation.
I have a rounded square texture, drawn in paint, with black border. How can I change only the inner color without changing the border color?
EDIT: I did it, but I want to ask if it can be done without using another texture? I also wonder if there is a connection between this and 9patch as in scaling. Can we use that or is there something like that?
You can tint whatever it is what you are drawing, using SpriteBatch. This means that color you specify is multiplied with the color of the image. For example if your image is a white rounded rectangle with a black border and you tint it using the color purple then the inside will be purple and the border will remain black. You didn't provide enough information to be more specific. But if you are for example using the Sprite class then you can use the setColor method to tint it. Likewise if you are using the Image class. If you are drawing the "texture" directly using SpriteBatch then you can use the setColor method of the SpriteBatch.
I am refering to a older question saying color blending with GDI+
Using GDI+ with Windows Forms, I want to be able to draw with a pen and blend color based on the destination pixel color.
For example, if I draw a line and it passes over black pixels, I want it to be a lighter color (like white for example) so that it's visible. When that same line passes over white pixels, it should be a darker color (black for example) so that it's still clearly visible.
the answers says to use a color matrix for transformation
so i started implementing it..
My image is present in raw data format in rgb48
Gdiplus::Bitmap image(input.width,input.height,input.width*6,PixelFormat48bppRGB,(unsigned char*)rgb48);
Gdiplus::Image *images= image.GetThumbnailImage(input.width,input.height);
Gdiplus::TextureBrush brush(images);
Gdiplus::Pen pen(&brush);
Gdiplus::ColorMatrix matrix={
-1.0f,0.0f,0.0f,0.0f,0.0f,
0.0f,-1.0f,0.0f,0.0f,0.0f,
0.0f,0.0f,-1.0f,0.0f,0.0f,
0.0f,0.0f,0.0f,1.0f,0.0f,
1.0f,1.0f,1.0f,0.0f,1.0f,
};
Gdiplus::Graphics gfx(&image1);
Gdiplus::ImageAttributes imageAttr;
imageAttr.SetColorMatrix(&matrix);
gfx.DrawImage(images,Gdiplus::Rect(0,0,input.width,input.height),0,0,1024,1024,Gdiplus::UnitPixel,&imageAttr);
I am not getting what i expect..Can some one help me in finding the mistake i m doing.
You can use the alpha component of a color to specify transparency, so that colors can be combined. However, if you want the combination to be something other than the alpha blend, you must draw the pixels yourself. You could first draw into a transparent bitmap, then render that onto the destination pixel by pixel.
When rendering textures that have an alpha-channel, a white border appears around the non-transparent part (the border seems to be the pixels that have an alpha > 0 and < 1):
The original texture is created in illustrator and exported as a png. here it is:
(well, seems stackoverflow altered the image, adjusting pixels that are not completely opaque/transparent, so here is a link)
it is probably the blending, though i dont know what is wrong with the setup:
gl.enable(gl.BLEND);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
[Update]
Here is a rendered version, where i added a alpha-gradient to the left part of the texture (so it is getting from 0 opacity to 1 until the half)
this texture is the only texture rendered at this position. it seems to be whitest around a=0.5. really weird. the background is just a cleared color:
gl.clearColor(0.603, 0.76, 0.804, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
// render objects here
the depth-function looks like:
gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);
any ideas? thanks a lot.
[Update 2]
Answering my own question: the effect occurs when the background-color of the canvas or the body of the html-page is white. I don't have an explanation, though.
Use premultiplied alpha and this problem will go away.
See: http://home.comcast.net/~tom_forsyth/blog.wiki.html#%5B%5BPremultiplied%20alpha%5D%5D
This is problem related to texturing linear interpolation. On borders, some interpolated pixels will take half white half green, and 0.5 alpha. You should modify your texture to extend your borders with one more green pixel, even if it is totally transparent.
What's your draw order? This looks like a depth buffering issue to me — you start with a white background, draw the thing with the border so that it's composited on the white, then draw the thing behind the thing with the border. Those areas where the border was blended with the original white background will have stored a value in the depth buffer equal to the depth of their plane, so when the object behind is subsequently drawn, its pixels are discarded in that area.
The general rule is to draw transparent objects after opaque objects, usually from back to front. If you're using additive blending then it's often good enough to disable the depth buffer after the opaque draw and draw them in any order.
When setting the FragColor in the shader, try multiplying the image RGB with the image alpha.
I have a randomly colored background that is split into solid colored rectangles. I want to draw a grid over the rectangles (this is not the problem). The issue is because of the random colors I cannot hard-code the grid color because it may not show up.
Another way to think about this is plotting a grid on a plot of a surface f(x,y). If the grid color happens to be the same color of the function (however it is defined) then it won't be visible.
I would like to take the background color and compute a new color (either grayscale or similar to the background color) that is contrasted with the color so it can easily be seen (but not distracting such as pure white on pure black).
I've tried using the luminance and weighted luminance but it doesn't work well for all colors. I've also tried gamma correcting the colors but it also does not work well.
I would also like the grid color to be as uniform as possible (I could possibly compute the adjacent grid colors to blend in). It is not that important but would be nice to have some uniformity.
The code I'm working with is based around
//byte I = (byte)(0.2*R + 0.7*G + 0.1*B);
//byte I = (byte)(R + G + B)/3.0);
byte I = (byte)(Math.Max(Bar.Background.R, Math.Max(Bar.Background.G, Bar.Background.B)));
if (I < 120)
I = (byte)(I + 30);
else
I = (byte)(I - 30);
//I = (byte)(Math.Pow(I/255.0, 1/2.0)*255);
I've also tried gamma correcting the rgb's first.
Anyone have any ideas?
The colors that offer the most contrast are colors that are fully saturated. This offers you a way to find color that may work(but not necessarily for many reasons). Essentially you pick the color the furthest away along the line connecting color and the fully saturated color.