UIKit Images
UIkit都是圍繞UIImage類的,我們可以從file或者NSData中創(chuàng)建一個(gè)UIImage,同時(shí)通過UIImageView顯示這個(gè)UIImage.我們也可以使用CoreGraphic直接繪制一個(gè)Image:
UIImage *SwatchWithColor(UIColor *color, CGFloat side){
// Create image context(using the main screen scale)
UIGraphicsBeginImageContextWithOptions(CGSizeMake(side, side), NO, 0.0);
// 開始繪制
[color setFill];
UIRectFill(CGRectMake(0, 0, side, side));
// 獲取圖片
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
對(duì)于Image需要記住以下要點(diǎn):
- 如果要知道一個(gè)圖像的范圍extent,直接使用
size屬性,這個(gè)屬性返回的單位是點(diǎn)point而不是像素pixel,具體的像素范圍和具體的mainscreen scale相關(guān).如果是retina屏幕1 point = 2 pixel. - 我們可以將UIImage壓縮成
png或者jpg-UIImagePNGRepresentation,UIImageJPEGRepresentation.這兩個(gè)方法是將UIImage轉(zhuǎn)化成壓縮以后的NSData. - 可以直接從UIImage中獲取image的Quartz表示CGImage - 可以這樣說UIImage是對(duì)CGImage(或者Core Image)的輕量級(jí)包裝.
Building Thumbnails
通常將一個(gè)大圖轉(zhuǎn)化成小圖賴創(chuàng)建縮略圖,一般使用image的drawRect方法繪制到目標(biāo)大小的rect中:
// 獲取context!!!
UIImage *image = [UIImage imageNamed:@"myImage"];
[image drawInRect:destinationRect];
UIImage *thumbnail = UIGraphicsGetImageFromCurrentImageContext();
通常創(chuàng)建縮略圖需要進(jìn)行取舍,究竟是Filling rect,還是Fitting Rect:
UIImage *BuildingThumnail(UIImage *sourceImage, CGSize targetSize, BOOL useFitting){
UIGraphicsBeginImageContextWithOptions(targetSize, NO, 0.0);
CGRect targetRect = SizeMakeRect(targetSize);
// 創(chuàng)建source Image 的bounding rect
CGRect naturalRect = (CGRect){.size = sourceImage.size};
// 計(jì)算 fitting 或者 filling dest rectangle, 使用Rect工具中的工具方法
CGRect destinationRect = useFitting ? RectByFittingRect(naturalRect, targetRect) : RectByFillingRect(naturalRect, targetRect);
// Draw the new thumbnail
[sourceImage drawInRect:destinationRect];
// Retrieve and return the new image
UIImage *thumbnail = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return thumbnail;
}
Extracting Subimages
與獲取縮略圖不同,獲取子圖片無需壓縮圖片的大小,它只需要獲取圖片中的部分內(nèi)容即可,其中的核心方法是CGImageCreateWithImageInRect()
// 所有的單位都是像素
UIImage *ExtractRectFromImage(UIImage *sourceImage, CGRect subRect){
// Extract image
CGImageRef imageRef = CGImageCreateWithImageInRect(sourceImage.CGImage, subRect);
if (imageRef != NULL) {
UIImage *output = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
return output;
}
return nil;
}
Converting an Image to Grayscale
將圖片繪制成grayscale模式.其中最核心的grayscale方法是GrayscaleVersionOfImage,全部的demo code:
UIImage *GrayscaleVersionOfImage(UIImage *sourceImage){
// Establish grayscale color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
if (colorSpace == NULL) {
return nil;
}
// Extents are integers
int width = sourceImage.size.width;
int height = sourceImage.size.height;
// Build context: one byte per pixel, no alpha
CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, width, colorSpace, (CGBitmapInfo)kCGImageAlphaNone);
if (context == NULL) {
return nil;
}
// Replicate image using new color space
CGRect rect = CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height);
CGContextDrawImage(context, rect, sourceImage.CGImage);
CGImageRef imageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
// Return the grayscale image
UIImage *output = [UIImage imageWithCGImage:imageRef];
CFRelease(imageRef);
return output;
}
Watermarking Images
有時(shí)候我們需要給圖片加上水印.
-(UIImage *)WatermarkingAnImage{
CGSize targetSize = CGSizeMake(200, 200);
UIGraphicsBeginImageContextWithOptions(targetSize, NO, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
// Draw the original image into the context
CGRect targetRect = SizeMakeRect(targetSize);
UIImage *sourceImage = [UIImage imageNamed:@"pronghorn.jpg"];
CGRect imgRect = RectByFillingRect(SizeMakeRect(sourceImage.size), targetRect); [sourceImage drawInRect:imgRect];
// Rotate the context
CGPoint center = RectGetCenter(targetRect);
CGContextTranslateCTM(context, center.x, center.y);
CGContextRotateCTM(context, M_PI_4);
CGContextTranslateCTM(context, -center.x, -center.y);
// Create a string
NSString *watermark = @"watermark";
UIFont *font = [UIFont fontWithName:@"HelveticaNeue" size:48];
CGSize size = [watermark sizeWithAttributes:@{NSFontAttributeName: font}];
CGRect stringRect = RectCenteredInRect(SizeMakeRect(size), targetRect);
// Retrieve the new image UIImage *image =
UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
Retrieving Image Data
一般情況下,我們都可以通過PNG或者JPEG方式獲取圖片的data形式,但是這些data形式里除了圖片的數(shù)據(jù),還包括了圖片的marker data等附加信息.如果我們需要獲取純圖片的data數(shù)據(jù) byte array,我們就需要直接使用context,來獲取source data.
Creating Contexts
我們之前已經(jīng)使用過CGBitmapContextCreate,這個(gè)方法需要如下幾個(gè)參數(shù):
- void *data - 一般傳入NULL.
- size_t width and size_t height - image寬和高,通過
CGBitmapContextCreate獲取的圖片的寬和高 - size_t bitsPerComponent - 在UIKit中,我們一般使用的8-bit bytes,一般傳入為8.
- size_t bytesPerRow - multiply the size of the row by the bytes per component
- CGColorSpaceRef colorspac e— You pass the color space Quartz should use to create the bitmap context, typically device RGB or device gray.
- CGBitmapInfo bitmapInfo—This parameter specifies the style of alpha channel the bitmap uses.一般使用kCGImageAlphaPremultipliedFirst(彩色圖片),或者kCGImageAlphaNone(grayscale)
Extracting Bytes的demo
NSData *BytesFromRGBImage(UIImage *sourceImage) {
if (!sourceImage) return nil;
// Establish color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
if (colorSpace == NULL){
NSLog(@"Error creating RGB color space");
return nil; }
// Establish context
int width = sourceImage.size.width;
int height = sourceImage.size.height;
CGContextRef context = CGBitmapContextCreate(NULL,
width,
height,
8, // bits per byte
width * 4, // bytes per row
colorSpace,
(CGBitmapInfo) kCGImageAlphaPremultipliedFirst);
CGColorSpaceRelease(colorSpace);
if (context == NULL){
NSLog(@"Error creating context");
return nil;
}
// Draw source into context bytes
CGRect rect = (CGRect){.size = sourceImage.size};
CGContextDrawImage(context, rect, sourceImage.CGImage);
// Create NSData from bytes
NSData *data = [NSData dataWithBytes:CGBitmapContextGetData(context) length:(width * height * 4)]; // bytes per image
CGContextRelease(context);
return data;
}
Creating Images from Bytes
與上一個(gè)步驟相反
#define BITS_PER_COMPONENT 8
#define ARGB_COUNT 4
UIImage *ImageFromBytes(NSData *data, CGSize targetSize) {
// Check data
int width = targetSize.width;
int height = targetSize.height;
if (data.length < (width * height * 4)) {
NSLog(@"Error: Got %d bytes. Expected %d bytes", data.length, width * height * 4);
return nil;
}
// Create a color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
if (colorSpace == NULL) {
NSLog(@"Error creating RGB colorspace");
return nil;
}
// Create the bitmap context
Byte *bytes = (Byte *) data.bytes;
CGContextRef context = CGBitmapContextCreate(bytes,
width,
height,
BITS_PER_COMPONENT, // 8 bits per component
width * ARGB_COUNT, // 4 bytes in ARGB
colorSpace,
(CGBitmapInfo)kCGImageAlphaPremultipliedFirst);
CGColorSpaceRelease(colorSpace );
if (context == NULL){
NSLog(@"Error. Could not create context");
return nil; }
// Convert to image
CGImageRef imageRef = CGBitmapContextCreateImage(context); UIImage *image = [UIImage imageWithCGImage:imageRef];
// Clean up CGContextRelease(context); CFRelease(imageRef);
return image;
}
