我使用以下扩展方法来调整图像大小。当涉及到大分辨率图像时,即使我将输出大小设置为500x500像素,输出大小仍然是1000x1000像素
extension NSImage {
func resizeImage(width: CGFloat, _ height: CGFloat) -> NSImage {
let img = NSImage(size: CGSize(width:width, height:height))
img.lockFocus()
let ctx = NSGraphicsContext.current
ctx?.imageInterpolation = .high
self.draw(in: NSMakeRect(0, 0, width, height), from: NSMakeRect(0, 0, size.width, size.height), operation: .copy, fraction: 1)
img.unlockFocus()
return img
}
我做错了什么? 请建议
更新:
//SAVING
for x in fileArray {
var image = NSImage(contentsOf:x)!
let imageURL=outdir+"/"+"xxx"
image=image.resizeImage(width: CGFloat(rwidth), CGFloat(rheight))
saveimage(xdata: image, imageURL: imageURL, format: fileformat)
}
func saveimage(xdata:NSImage,imageURL:String,format:String) -> Bool
{
let bMImg = NSBitmapImageRep(data: (xdata.tiffRepresentation)!)
switch format {
case ".png":
let filepath=URL(fileURLWithPath: imageURL+".png")
let dataToSave = bMImg?.representation(using: NSBitmapImageRep.FileType.png, properties: [NSBitmapImageRep.PropertyKey.compressionFactor : 1])
do
{
try dataToSave?.write(to: filepath)
return true
} catch
{
return false
}
case ".jpg":
let filepath=URL(fileURLWithPath: imageURL+".jpg")
let dataToSave = bMImg?.representation(using: NSBitmapImageRep.FileType.jpeg, properties: [NSBitmapImageRep.PropertyKey.compressionFactor : 1])
do
{
try dataToSave?.write(to:filepath)
return true
} catch
{
return false
}
case ".tif":
let filepath=URL(fileURLWithPath: imageURL+".tif")
let dataToSave = bMImg?.representation(using: NSBitmapImageRep.FileType.tiff, properties: [NSBitmapImageRep.PropertyKey.compressionFactor : 1])
do
{
try dataToSave?.write(to:filepath)
return true
} catch
{
return false
}
case ".bmp":
let filepath=URL(fileURLWithPath: imageURL+".bmp")
let dataToSave = bMImg?.representation(using: NSBitmapImageRep.FileType.bmp, properties: [NSBitmapImageRep.PropertyKey.compressionFactor : 1])
do
{
try dataToSave?.write(to:filepath)
return true
} catch
{
return false
}
case ".gif":
let filepath=URL(fileURLWithPath: imageURL+".gif")
let dataToSave = bMImg?.representation(using: NSBitmapImageRep.FileType.gif, properties: [NSBitmapImageRep.PropertyKey.compressionFactor : 1])
do
{
try dataToSave?.write(to:filepath)
return true
} catch
{
return false
}
default:
return true
}
}
答案 0 :(得分:0)
问题是您没有考虑到您正在创建的图片的比例。
你有一个Retina屏幕。当您调用lockFocus
并绘制到生成的图形上下文时,图形上下文具有双重分辨率。因此,500x500的大小导致底层位图为1000x1000。这对于展示来说并不重要;只要它确实重要,它就是一件好事。
但是当你继续将图像数据保存到磁盘时,你就会忘记这是一个双分辨率图像,你只需保存位图 - 即1000x1000。
您应该查看Apple有关如何处理高分辨率图像的文档,例如: https://developer.apple.com/library/content/documentation/GraphicsAnimation/Conceptual/HighResolutionOSX/APIs/APIs.html