Create UIImage of a specific size

Question

How can I create a UIImage from scratch. Specifically, I want to create a UIImage of size 320x50. Then, I'd like to be able to draw polygons of specific color onto that image.

You can draw images easily using Quartz Graphics. If I understand correctly you just want to draw something on an image? Well in Quartz Graphics you can just draw things on top of that drawn image after Quartz Graphics is done with drawing the image. You should probably want to look that up ;) — Totumus Maximus, Jan 16 '12 at 08:37

score 5 · Accepted Answer · edited May 23 '17 at 12:03

Here is an answer for you stitch picture in iphone

And base on my experience, I can give you some note:

Propotional scale

- (UIImage *)scaleImage:(UIImage *)image toScale:(float)scaleSize
{
 UIGraphicsBeginImageContext(CGSizeMake(image.size.width*scaleSize,image.size.height*scaleSize);
 [image drawInRect:CGRectMake(0, 0, image.size.width * scaleSize, image.size.height *scaleSize)];
 UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 return scaledImage;
}

Resize

- (UIImage *)reSizeImage:(UIImage *)image toSize:(CGSize)reSize
{
 UIGraphicsBeginImageContext(CGSizeMake(reSize.width, reSize.height));
 [image drawInRect:CGRectMake(0, 0, reSize.width, reSize.height)];
 UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 return reSizeImage;
}

Handle specific view

You hava to import QuzrtzCore.framework first

-(UIImage*)captureView:(UIView *)theView
{
 CGRect rect = theView.frame; 
 UIGraphicsBeginImageContext(rect.size); 
 CGContextRef context = UIGraphicsGetCurrentContext(); 
 [theView.layer renderInContext:context]; 
 UIImage *img = UIGraphicsGetImageFromCurrentImageContext(); 
 UIGraphicsEndImageContext(); 
 return img;
}

Handle a range form image

CGRect captureRect = yourRect
CGRect viewRect = self.view.frame;
UIImage *viewImg;
UIImage *captureImg;

UIGraphicsBeginImageContext(viewRect.size); 
CGContextRef context = UIGraphicsGetCurrentContext(); 
[self.view.layer renderInContext:context]; 
viewImg = UIGraphicsGetImageFromCurrentImageContext(); 
UIGraphicsEndImageContext();

captureImg = [UIImage imageWithCGImage:CGImageCreateWithImageInRect(viewImg.CGImage, captureRect)];

Save the image

Save in app

NSString *path = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"image.png"];
[UIImagePNGRepresentation(image) writeToFile:path atomically:YES];

Save in album

CGImageRef screen = UIGetScreenImage();
UIImage* image = [UIImage imageWithCGImage:screen];
CGImageRelease(screen);
UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);

thank you for this extensive response, however I'm not sure what some of these things mean, such as "handle a range form image"...which one would I use to simply do something like UIImage *newImage = [oldImage drawPolygonOnOldImage:polygon]; — CodeGuy, Jan 16 '12 at 19:57

TomCobo · Answer 2 · 2021-02-17T16:19:21.307

I leave here my answer, just in case this can help in the future. This answer is valid on iOS10+

extension UIImage {
    static func image(with size: CGSize) -> UIImage {
        UIGraphicsImageRenderer(size: size)
            .image { $0.fill(CGRect(origin: .zero, size: size)) }
    }
}

so you can do: UIImage.image(with: CGSize(width: 320, height: 50))

My answer is inspired by this: https://stackoverflow.com/a/48441178/2000162

score 2 · Answer 3 · answered Jan 16 '12 at 08:41

2

You can:

Create a CGBitmapContext using the color/pixel/dimensions/etc you will need.
Use the context or manipulate pixels directly.
Create a UIImage using the result of CGBitmapContextCreateImage

answered Jan 16 '12 at 08:41

justin

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Create UIImage of a specific size

3 Answers3