I'm creating a mask based on DeviceGray color space based image.
What basically I want to do is to change all sorts of gray (beside black) pixels into white and leave black pixels as they are.
So I want my image to be consisted with black and white pixels.
Any idea how to achieve that using CoreGraphics means ?
Please dont offer running all over the pixels in the loop
Use CGImageCreateWithMaskingColors and CGContextSetRGBFillColor together like this:
CGImageRef myMaskedImage;
const CGFloat myMaskingColors[6] = { 0, 124, 0, 68, 0, 0 };
myColorMaskedImage = CGImageCreateWithMaskingColors (image,
myMaskingColors);
CGContextSetRGBFillColor (myContext, 0.6373,0.6373, 0, 1);
CGContextFillRect(context, rect);
CGContextDrawImage(context, rect, myColorMaskedImage);
By the way, the fill color is mentioned at the CGImageCreateWithMaskingColors discussion.
Related
I am new to Iphone development.
Currently i am making coloring app.
I am using apple's paint app as ref to create my app.
I successfully create app where u can color on a screen with given texture image
What i did is
I create a custom UIView which extends opengl and i detect touches on it and draw accordingly.
I also kept background UIImageView which contain outline images, so it feels like your drawing above that Image.
Everything works fine
but i wanted to fill color inside black edges
Like if a image has four square which has black edges and inside of that square is blank and if i touch any square it should fill that square with selected color(mostly i am working on irregular shape)
Can anyone tell me how can i fill colors inside that square
The flood fill algo looks slow as i have some big images which will take time to fill the color
so is there any easy method by which i can fill color
A sample code will b very helpful as i am new to iPhone Dev
I implemnted this kind of feature in my recent project. The difference is: I filled color in border only.
Check my code over here, it might get helpful to you
// apply color to only border & return an image
+ (UIImage *)imageNamed:(NSString *)name withColor:(UIColor *)color
{
// load the image
UIImage *img = [UIImage imageNamed:name];
// begin a new image context, to draw our colored image onto
UIGraphicsBeginImageContext(img.size);
// get a reference to that context we created
CGContextRef context = UIGraphicsGetCurrentContext();
// set the fill color
[color setFill];
// translate/flip the graphics context (for transforming from CG* coords to UI* coords
CGContextTranslateCTM(context, 0, img.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
// set the blend mode to color burn, and the original image
CGContextSetBlendMode(context, kCGBlendModeColorBurn);
CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
CGContextDrawImage(context, rect, img.CGImage);
// set a mask that matches the shape of the image, then draw (color burn) a colored rectangle
CGContextClipToMask(context, rect, img.CGImage);
CGContextAddRect(context, rect);
CGContextDrawPath(context,kCGPathFill);
// generate a new UIImage from the graphics context we drew onto
UIImage *coloredImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
//return the color-burned image
return coloredImg;
}
Enjoy Programming !
i'm really new to dealing with CGContexts and i'm just trying to get my head around things by following a simple touch paint & sketch tutorial (http://blog.effectiveui.com/?p=8105)
I have hit a brick wall when it's come to changing the background colour of my CGContext though.
I'm initiating the conext like this:
- (BOOL) initContext:(CGSize)size {
int bitmapBytesPerRow;
bitmapBytesPerRow = (size.width * 4);
cacheContext = CGBitmapContextCreate (nil, size.width, size.height, 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipLast);
CGContextSetRGBFillColor(cacheContext, 1, 1, 1, 1);
return YES;
}
and changing stroke colours and widths like this:
UIColor *color = [UIColor whiteColor];
CGContextSetStrokeColorWithColor(cacheContext, [color CGColor]);
CGContextSetLineCap(cacheContext, kCGLineCapRound);
CGContextSetLineWidth(cacheContext, 4);
but when i try to change the background colour from black (either in the init or in the drawing/stroke set-up parts) using CGContextSetRGBFillColor(cacheContext, 1, 1, 1, 1); there is no effect.
Is anyone able to point me in the right direction of either a better/correct place to put that call, or the correct call to use? Many thanks for your time!
You can't just set the color and expect the context to fill with the new color. You need to actually draw that color into the context. In the init method, after setting the fill color, try using something like
CGContextFillRect(cacheContext, (CGRect){CGPointZero, size});
On a related note, context don't have a black color by default. They have a transparent color. Now, if your context doesn't have an alpha channel, then this will end up being black, but if your context does have an alpha channel and you're seeing black, it's because you're rendering the output on top of something black (or, alternately, you're putting the transparent image into a layer that has the opaque flag set to true and CoreAnimation ends up drawing it on top of black).
I'm making a legend for a graph that will basically look like this:
[ ] Line 1
[ ] Line 2
[ ] Line 3
The boxes on the left need to be the same color as the lines on the graph.
Anyhow, all I need to know, is whether it's faster to draw the boxes with Core Graphics or just make some pngs with GIMP for the squares and include them.
Use UIView for each legend and set their background color to the color you want.
Both approaches are fast enough that it shouldn't make a difference. However, using Core Graphics has the advantage that you're a lot more flexible, e.g. when you later decide that you need additional colors. Plus, your app will be smaller, because you don't have to include the PNG files.
Drawing boxes is a snap! I would go with Core Graphics everyday, especially since you get retina support for free.
As can be seen in this example you can do it using UIKit only classes:
// Setup colors
[myBoxColor setFill];
[myBoxBorderColor set];
// Setup a path for the box
UIBezierPath* path = [UIBezierBath bezierPathWithRect:rectOfTheBox];
path.lineWidth = 2;
// Draw!
[path fill];
[path stroke];
One warning; stroke fills using the edges of the path as the center of the line. So you will get a blurry line if you stroke a path with integral rect with a 1 point line width.
You can remedy this is you want a 1 point line for the border by doing something like this:
CGRect strokeRect = UIEdgeInsetsInsetRect(rectOfTheBox,
UIEdgeInsetsMake(0.5f,0.5f,0.5f,0.5f));
UIBezierPath* path = [UIBezierPath bezierPathWithRect:strokeRect];
[path stroke];
On iOS, Core Graphics is quite simple to use. In your view's drawRect: method, just do this to draw a square:
- (void)drawRect:(CGRect)frame {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBFillColor(context, 0.5, 0.5, 0.5, 1); // gray
CGContextFillRect(context, CGRectMake(10, 10, 20, 20)); // our rect is {10,10,20,20)
// draw a line
CGContextSetRGBStrokeColor(context, 1, 0, 0, 1);
CGContextBeginPath(context);
CGContextMoveToPoint(context, startX, startY);
CGContextAddLineToPoint(context, endX, endY);
CGContextStrokePath(context);
}
Hope this helps!
Using CoreGraphics (inside my drawRect method), I'm trying to apply a blend mode to an image (transparent png), and then adjust the alpha of the result. I'm assuming that this needs to be done in two steps, but I could be wrong. Here's what I have so far (which works fine):
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
//SET COLOR - EDIT... added a more practical color example
CGContextSetRGBFillColor(context, 0.0, 1.0, 0.0, 1);
//flips drawing context (apparently this is necessary)
CGContextTranslateCTM(context, 0.0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);//flip context
//DRAW PIN IMAGE
UIImage *pin = [UIImage imageNamed:#"pin"];
CGRect pinrect = CGRectMake(12, 17, 25, 25);
CGContextDrawImage(context, pinrect, pin.CGImage);//draws image in context
//Apply blend mode
CGContextSetBlendMode(context, kCGBlendModeColor);
CGContextClipToMask(context, pinrect, pin.CGImage); // restricts drawing to within alpha channel
//fills context with mask, applying blend mode
CGContextFillRect(context, pinrect);
CGContextRestoreGState(context);
// -- Do something here to make result 50% transparent ?? --
I'm assuming that I need to draw all this into some kind of separate context somewhere, call CGContextSetAlpha(...), and then re-draw it back to my original context, but I'm not sure how. Setting the alpha before my final CGContextFillRect will just change the amount that the blend mode was applied, not the alpha of the entire image.
EDIT: screenshot posted
Thanks in advance.
Using transparency layers, you can apply the blend to an image drawn at 100% and display the result at 50%. The result looks like this:
I used the textured background so that you could clearly see that the lower image is 50% transparent to everything, instead of just the other image as was the case in my previous attempt. Here is the code:
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0.0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);//flip context
CGRect fullImageRect = (CGRect){42,57,100,100};
CGRect transparentImageRect = (CGRect){12,17,100,100};
CGContextSetRGBFillColor(context, 0.0, 1.0, 0.0, 1);
// Draw image at 100%
UIImage *testImage = [UIImage imageNamed:#"TestImage"];
CGContextDrawImage(context,fullImageRect,testImage.CGImage);
// Set 50% transparency and begin a transparency layer. Inside the transparency layer, the alpha is automatically reset to 1.0
CGContextSetAlpha(context,0.5);
CGContextBeginTransparencyLayer(context, NULL);
// Draw the image. It is viewed at 100% within the transparency layer and 50% outside the transparency layer.
CGContextDrawImage(context, transparentImageRect, testImage.CGImage);
// Draw blend on top of image
CGContextClipToMask(context, transparentImageRect, testImage.CGImage);
CGContextSetBlendMode(context, kCGBlendModeColor);
CGContextFillRect(context, transparentImageRect);
// Exit transparency layer, causing the image and blend to be composited at 50%.
CGContextEndTransparencyLayer(context);
Edit: Old content removed as it took a lot of space and wasn't helpful. Look in the revision history if you want to see it.
I'm using CGImageCreateWithImageInRect to do a magnifying effect, and it works beautifully, except when I get close to the edges of my view. In that case, clipping causes the image to be distorted. Right now I grab a 72x72 chunk of the view, apply a round mask to it, and then draw the masked image, and a circle on top.
When the copied chunk is near the edge of the view, It winds up smaller than 72x72 because of clipping, and then when it's drawn in the magnifying glass it gets stretched out.
When the touch point is close to the left edge, for example, I would like to create an image where the left part is filled with a solid color, and the right half contains part of the view that's being magnified. Then apply the mask to that image and add the overlay on top.
Here's what I'm doing now. imageRef is the image being magnified, mask is a round mask, and overlay is a circle to mark the edges of the magnified region.
CGImageRef subImage = CGImageCreateWithImageInRect(imageRef, CGRectMake(touchPoint.x - 36, touchPoint.y - 36, 72, 72));
CGImageRef xMaskedImage = CGImageCreateWithMask(subImage, mask);
CGContextRef context = UIGraphicsGetCurrentContext();
CGAffineTransform xform = CGAffineTransformMake(1.0, 0.0, 0.0, -1.0, 0.0, 0.0);
CGContextConcatCTM(context, xform);
CGRect area = CGRectMake(touchPoint.x - 84, -touchPoint.y, 170, 170);
CGRect area2 = CGRectMake(touchPoint.x - 80, -touchPoint.y + 4, 160, 160);
CGContextDrawImage(context, area2, xMaskedImage);
CGContextDrawImage(context, area, overlay);
I solved this by using CGBitmapContextCreate() to create a bitmap context. Then I drew the captured area into a smaller area of this context, and created an image from it with CGBitmapContextCreateImage(). That was the missing piece of the puzzle.