如何在不丢失透明背景的情况下将 png 图像的文件大小减小到小于 64KB,并在 Swift 中保持 512 X 512 像素。
我试过这段代码:
func resizeImageOriginalSize(targetSize: CGSize) -> UIImage {
var actualHeight: Float = Float(self.size.height)
var actualWidth: Float = Float(self.size.width)
let maxHeight: Float = Float(targetSize.height)
let maxWidth: Float = Float(targetSize.width)
var imgRatio: Float = actualWidth / actualHeight
let maxRatio: Float = maxWidth / maxHeight
var compressionQuality: Float = 0.5
//50 percent compression
if actualHeight > maxHeight || actualWidth > maxWidth {
if imgRatio < maxRatio {
//adjust width according to maxHeight
imgRatio = maxHeight / actualHeight
actualWidth = imgRatio * actualWidth
actualHeight = maxHeight
}
else if imgRatio > maxRatio {
//adjust height according to maxWidth
imgRatio = maxWidth / actualWidth
actualHeight = imgRatio * actualHeight
actualWidth = maxWidth
}
else {
actualHeight = maxHeight
actualWidth = maxWidth
compressionQuality = 0.4
}
}
let rect = CGRect(x: 0.0, y: 0.0, width: CGFloat(actualWidth), height: CGFloat(actualHeight))
UIGraphicsBeginImageContextWithOptions(rect.size, false, CGFloat(compressionQuality))
self.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage!
}
但尺寸不是我预期的。
最佳答案
你应该检查WWDC Session 219 - Image and graphics best practices .它的前三分之一包含有关如何优化图形的有用信息,尤其是内存占用。
建议的方法之一是下采样技术。这是一个片段:
func downsample(imageAt imageURL: URL, to pointSize: CGSize, scale: CGFloat) -> UIImage {
let imageSourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary
let imageSource = CGImageSourceCreateWithURL(imageURL as CFURL, imageSourceOptions)!
let maxDimensionInPixels = max(pointSize.width, pointSize.height) * scale
let downsampleOptions =
[kCGImageSourceCreateThumbnailFromImageAlways: true,
kCGImageSourceShouldCacheImmediately: true,
kCGImageSourceCreateThumbnailWithTransform: true,
kCGImageSourceThumbnailMaxPixelSize: maxDimensionInPixels] as CFDictionary
let downsampledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, downsampleOptions)!
return UIImage(cgImage: downsampledImage)
}
下采样将根据下采样大小的变化按比例减少图像内存大小。此外,图像质量和内存占用之间始终存在权衡,结果在很大程度上取决于压缩算法和压缩设置。
这stackoverflow thread ,尤其是 this answer提供了一些提示。
希望对您有所帮助。
关于ios - 减少png图像的文件大小,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/53780468/