最佳方法是检查一个UIImage
是否为空白?
我有一个绘画编辑器,它会返回一个UIImage
;如果上面没有任何东西,我不想保存这个图片。
试试这段代码:
BOOL isImageFlag=[self checkIfImage:image];
并且检查 checkIfImage 方法:
- (BOOL) checkIfImage:(UIImage *)someImage {
CGImageRef image = someImage.CGImage;
size_t width = CGImageGetWidth(image);
size_t height = CGImageGetHeight(image);
GLubyte * imageData = malloc(width * height * 4);
int bytesPerPixel = 4;
int bytesPerRow = bytesPerPixel * width;
int bitsPerComponent = 8;
CGContextRef imageContext =
CGBitmapContextCreate(
imageData, width, height, bitsPerComponent, bytesPerRow, CGImageGetColorSpace(image),
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big
);
CGContextSetBlendMode(imageContext, kCGBlendModeCopy);
CGContextDrawImage(imageContext, CGRectMake(0, 0, width, height), image);
CGContextRelease(imageContext);
int byteIndex = 0;
BOOL imageExist = NO;
for ( ; byteIndex < width*height*4; byteIndex += 4) {
CGFloat red = ((GLubyte *)imageData)[byteIndex]/255.0f;
CGFloat green = ((GLubyte *)imageData)[byteIndex + 1]/255.0f;
CGFloat blue = ((GLubyte *)imageData)[byteIndex + 2]/255.0f;
CGFloat alpha = ((GLubyte *)imageData)[byteIndex + 3]/255.0f;
if( red != 1 || green != 1 || blue != 1 || alpha != 1 ){
imageExist = YES;
break;
}
}
free(imageData);
return imageExist;
}
您需要添加OpenGLES框架并在.m文件中导入它:
#import <OpenGLES/ES1/gl.h>
一个想法是调用UIImagePNGRepresentation函数获取一个NSData
对象,然后将其与预定义的“空”版本进行比较 - 即调用:
- (BOOL)isEqualToData:(NSData *)otherData
要测试吗?
如果你的图像数据很大,可能需要检查性能,但如果数据比较小,使用类似于C语言中的memcmp()
。
以下是相关内容的翻译:
CGContext
其他人可能会在此答案中添加更多详细信息。
这里提供了一种Swift的解决方案,不需要任何额外的框架。
感谢在这里相关问题中的答案: 如何在xcode上通过触摸屏幕的坐标获取ImageView的像素数据?
func imageIsEmpty(_ image: UIImage) -> Bool {
guard let cgImage = image.cgImage,
let dataProvider = cgImage.dataProvider else
{
return true
}
let pixelData = dataProvider.data
let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)
let imageWidth = Int(image.size.width)
let imageHeight = Int(image.size.height)
for x in 0..<imageWidth {
for y in 0..<imageHeight {
let pixelIndex = ((imageWidth * y) + x) * 4
let r = data[pixelIndex]
let g = data[pixelIndex + 1]
let b = data[pixelIndex + 2]
let a = data[pixelIndex + 3]
if a != 0 {
if r != 0 || g != 0 || b != 0 {
return false
}
}
}
}
return true
}
我不在我的Mac上,所以我无法测试这个(可能会有编译错误)。但是可能有一种方法:
//The pixel format depends on what sort of image you're expecting. If it's RGBA, this should work
typedef struct
{
uint8_t red;
uint8_t green;
uint8_t blue;
uint8_t alpha;
} MyPixel_T;
UIImage *myImage = [self doTheThingToGetTheImage];
CGImageRef myCGImage = [myImage CGImage];
//Get a bitmap context for the image
CGBitmapContextRef *bitmapContext =
CGBitmapContextFreate(NULL, CGImageGetWidth(myCGImage), CGImageGetHeight(myCGImage),
CGImageGetBitsPerComponent(myCGImage), CGImageGetBytesPerRow(myCGImage),
CGImageGetColorSpace(myCGImage), CGImageGetBitmapInfo(myCGImage));
//Draw the image into the context
CGContextDrawImage(bitmapContext, CGRectMake(0, 0, CGImageGetWidth(myCGImage), CGImageGetHeight(myCGImage)), myCGImage);
//Get pixel data for the image
MyPixel_T *pixels = CGBitmapContextGetData(bitmapContext);
size_t pixelCount = CGImageGetWidth(myCGImage) * CGImageGetHeight(myCGImage);
for(size_t i = 0; i < pixelCount; i++)
{
MyPixel_T p = pixels[i];
//Your definition of what's blank may differ from mine
if(p.red > 0 && p.green > 0 && p.blue > 0 && p.alpha > 0)
return NO;
}
return YES;
我刚遇到了同样的问题。通过检查尺寸解决了它:
Swift 示例:
let image = UIImage()
let height = image.size.height
let width = image.size.height
if (height > 0 && width > 0) {
// We have an image
} else {
// ...and we don't
}