What you want is called planar rectification, and it’s not all that simple, I’m afraid. What you need to do is recover the homography that maps this oblique view of the van side onto the front-facing view. Photoshop / etc. have tools to do this for you given some control points; if you want to … Read more
Similar to this question which asks about points instead of centimeters. There are 72 points per inch and there are 2.54 centimeters per inch, so just substitute 2.54 for 72 in the answer to that question. I’ll quote and correct my answer here: There are 2.54 centimeters per inch; if it is sufficient to assume … Read more
A pixel on iOS is the full resolution of the device, which means if I have an image that is 100×100 pixels in length, then the phone will render it 100×100 pixels on a standard non-retina device. However, because newer iPhones have a quadrupled pixel density, that same image will render at 100×100 pixels, but … Read more
You can write a script that creates and returns a .gif, .jpeg or .png image using PHP for tracking purposes using the GD library (which is often distributed with PHP in modern versions). If you don’t have access to GD, you can always recompile PHP with GD enabled. Example: pixel.php (commented for the purposes of … Read more
This is the one I’ve used, and it looks simpler than the methods you’ve tried. In my custom view class, I have this: – (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [[event allTouches] anyObject]; CGPoint loc = [touch locationInView:self]; self.pickedColor = [self colorOfPoint:loc]; } colorOfPoint is a method in a category on UIView, with … Read more
This took quite a while to figure out, mainly because I wanted to get it up and running in Swift using Core Image and CIColorCube. @Miguel’s explanation is spot on about the way you need to replace a “Hue angle range” with another “Hue angle range”. You can read his post above for details on … Read more
There are two best contenders: Create a 1×1 image data, set the color, and putImageData at the location: var id = myContext.createImageData(1,1); // only do this once per page var d = id.data; // only do this once per page d[0] = r; d[1] = g; d[2] = b; d[3] = a; myContext.putImageData( id, x, … Read more
Here is more efficient solution: // UIView+ColorOfPoint.h @interface UIView (ColorOfPoint) – (UIColor *) colorOfPoint:(CGPoint)point; @end // UIView+ColorOfPoint.m #import “UIView+ColorOfPoint.h” #import <QuartzCore/QuartzCore.h> @implementation UIView (ColorOfPoint) – (UIColor *) colorOfPoint:(CGPoint)point { unsigned char pixel[4] = {0}; CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, kCGBitmapAlphaInfoMask & kCGImageAlphaPremultipliedLast); CGContextTranslateCTM(context, -point.x, -point.y); [self.layer renderInContext:context]; … Read more
There is no “320×240 glOrtho canvas”. There is only the window’s actual resolution: 960×720. All you are doing is scaling up the coordinates of the primitives you render. So, your code says to render a line from, for example, (20, 20) to (40, 40). And OpenGL (eventually) scales those coordinates by 3 in each dimension: … Read more
DP to PX: public static int dpToPx(float dp, Context context) { return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, context.getResources().getDisplayMetrics()); } SP to PX: public static int spToPx(float sp, Context context) { return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp, context.getResources().getDisplayMetrics()); } DP to SP: public static int dpToSp(float dp, Context context) { return (int) (dpToPx(dp, context) / context.getResources().getDisplayMetrics().scaledDensity); }