我在Xamarin.Forms项目中使用SkiaSharp中的SKBitmap.Resize（）方法调整图像大小以供显示。我遇到的问题是在iOS上拍照时，当以肖像拍摄照片时，图像会以正面朝上显示。在Android上拍照，从Android和iOS设备上的照片库导入可以保持方向，但在iOS上拍照不会。如果我不使用SkiaSharp调整图像大小（仅显示图像而不调整大小），则图像将以正确的方向显示。然而，这不是解决方案，因为图像需要调整大小。以下是我的代码 -
private byte[] GetResizedImageData(string imageName)
{
float resizeFactor = 0.5f;
var filePath = PathUtil.GetImagePath(imageName);
var ogBitmap = SKBitmap.Decode(filePath);
float fWidth = ogBitmap.Width * resizeFactor;
int width = (int) Math.Round(fWidth);
float fHeight = ogBitmap.Height * resizeFactor;
int height = (int) Math.Round(fHeight);
if (height >= 4096 || width >= 4096)
{
width = width * (int)resizeFactor;
height = height * (int)resizeFactor;
}
var scaledBitmap = ogBitmap.Resize(new SKImageInfo( width, height), SKBitmapResizeMethod.Box);
var image = SKImage.FromBitmap(scaledBitmap);
var data = image.Encode(SKEncodedImageFormat.Jpeg, 100);
return data.ToArray();
}
PathUtil.GetImagePath（）只是获取照片存储位置的特定于平台的路径的帮手。
答案 0 :(得分：7)
对于那些有同样问题的人，我做了以下事情，很乐意接受有关改进的意见。
public static SKBitmap HandleOrientation(SKBitmap bitmap, SKCodecOrigin orientation)
{
SKBitmap rotated;
switch (orientation)
{
case SKCodecOrigin.BottomRight:
using (var surface = new SKCanvas(bitmap))
{
surface.RotateDegrees(180, bitmap.Width / 2, bitmap.Height / 2);
surface.DrawBitmap(bitmap.Copy(), 0, 0);
}
return bitmap;
case SKCodecOrigin.RightTop:
rotated = new SKBitmap(bitmap.Height, bitmap.Width);
using (var surface = new SKCanvas(rotated))
{
surface.Translate(rotated.Width, 0);
surface.RotateDegrees(90);
surface.DrawBitmap(bitmap, 0, 0);
}
return rotated;
case SKCodecOrigin.LeftBottom:
rotated = new SKBitmap(bitmap.Height, bitmap.Width);
using (var surface = new SKCanvas(rotated))
{
surface.Translate(0, rotated.Height);
surface.RotateDegrees(270);
surface.DrawBitmap(bitmap, 0, 0);
}
return rotated;
default:
return bitmap;
}
然后使用以下内容获取原始方向。
// TODO: Improve this.. I do not know how to "reset"
// the inputStream, so new it up twice. :/
using (var inputStream = new SKManagedStream(imageIn))
{
using (var codec = SKCodec.Create(inputStream))
{
orientation = codec.Origin;
}
}
....... 然后
SKBitmap orientedWExif = HandleOrientation(resized, orientation);
答案 1 :(得分：2)
SkiaSharp实际上并没有提供一种操作和改变图像方向的方法。最后，当我捕获并使用平台特定代码保存图像时，我最终改变了方向。
答案 2 :(得分：1)
用于调整大小和方向的可行解决方案
public class ImageResizer : IImageResizer
{
private const int Quality = 75;
public byte[] Resize(byte[] data, int newWidth, int newHeight)
{
using (var inputStream = new SKMemoryStream(data))
{
using (var codec = SKCodec.Create(inputStream))
{
using (var original_old = SKBitmap.Decode(codec))
{
int sourceWidth = original_old.Width;
int sourceHeight = original_old.Height;
float nPercentW = ((float) newWidth / (float) sourceWidth);
float nPercentH = ((float) newHeight / (float) sourceHeight);
float nPercent = nPercentH < nPercentW ? nPercentH : nPercentW;
int destWidth = (int) (sourceWidth * nPercent);
int destHeight = (int) (sourceHeight * nPercent);
using (SKBitmap original = original_old.Resize(new SKImageInfo(destWidth, destHeight), SKFilterQuality.Medium))
{
var useWidth = original.Width;
var useHeight = original.Height;
Action<SKCanvas> transform = canvas => { };
switch (codec.EncodedOrigin)
{
case SKEncodedOrigin.TopLeft:
break;
case SKEncodedOrigin.TopRight:
// flip along the x-axis
transform = canvas => canvas.Scale(-1, 1, useWidth / 2, useHeight / 2);
break;
case SKEncodedOrigin.BottomRight:
transform = canvas => canvas.RotateDegrees(180, useWidth / 2, useHeight / 2);
break;
case SKEncodedOrigin.BottomLeft:
// flip along the y-axis
transform = canvas => canvas.Scale(1, -1, useWidth / 2, useHeight / 2);
break;
case SKEncodedOrigin.LeftTop:
useWidth = original.Height;
useHeight = original.Width;
transform = canvas =>
{
// Rotate 90
canvas.RotateDegrees(90, useWidth / 2, useHeight / 2);
canvas.Scale(useHeight * 1.0f / useWidth, -useWidth * 1.0f / useHeight, useWidth / 2, useHeight / 2);
};
break;
case SKEncodedOrigin.RightTop:
useWidth = original.Height;
useHeight = original.Width;
transform = canvas =>
{
// Rotate 90
canvas.RotateDegrees(90, useWidth / 2, useHeight / 2);
canvas.Scale(useHeight * 1.0f / useWidth, useWidth * 1.0f / useHeight, useWidth / 2, useHeight / 2);
};
break;
case SKEncodedOrigin.RightBottom:
useWidth = original.Height;
useHeight = original.Width;
transform = canvas =>
{
// Rotate 90
canvas.RotateDegrees(90, useWidth / 2, useHeight / 2);
canvas.Scale(-useHeight * 1.0f / useWidth, useWidth * 1.0f / useHeight, useWidth / 2, useHeight / 2);
};
break;
case SKEncodedOrigin.LeftBottom:
useWidth = original.Height;
useHeight = original.Width;
transform = canvas =>
{
// Rotate 90
canvas.RotateDegrees(90, useWidth / 2, useHeight / 2);
canvas.Scale(-useHeight * 1.0f / useWidth, -useWidth * 1.0f / useHeight, useWidth / 2, useHeight / 2);
};
break;
}
var info = new SKImageInfo(useWidth, useHeight);
using (var surface = SKSurface.Create(info))
{
using (var paint = new SKPaint())
{
// high quality with antialiasing
paint.IsAntialias = true;
paint.FilterQuality = SKFilterQuality.High;
// rotate according to origin
transform.Invoke(surface.Canvas);
// draw the bitmap to fill the surface
surface.Canvas.DrawBitmap(original, info.Rect, paint);
surface.Canvas.Flush();
using (SKImage image = surface.Snapshot())
{
return image.Encode(SKEncodedImageFormat.Jpeg, Quality).ToArray();
}
}
}
}
}
}
}
}
}
答案 3 :(得分：0)
谢谢@ttugates，您的回答帮助我解决了方向旋转问题。只是想更新您的答案，因为有一些不推荐使用的代码。
using (var inputStream = new SKManagedStream(await file.ReadAllStreamAsync()))
{
using (var codec = SKCodec.Create(inputStream))
{
orientation = codec.EncodedOrigin;
}
}
public static SKBitmap HandleOrientation(SKBitmap bitmap, SKEncodedOrigin orientation)
{
SKBitmap rotated;
switch (orientation)
{
case SKEncodedOrigin.BottomRight:
using (var surface = new SKCanvas(bitmap))
{
surface.RotateDegrees(180, bitmap.Width / 2, bitmap.Height / 2);
surface.DrawBitmap(bitmap.Copy(), 0, 0);
}
return bitmap;
case SKEncodedOrigin.RightTop:
rotated = new SKBitmap(bitmap.Height, bitmap.Width);
using (var surface = new SKCanvas(rotated))
{
surface.Translate(rotated.Width, 0);
surface.RotateDegrees(90);
surface.DrawBitmap(bitmap, 0, 0);
}
return rotated;
case SKEncodedOrigin.LeftBottom:
rotated = new SKBitmap(bitmap.Height, bitmap.Width);
using (var surface = new SKCanvas(rotated))
{
surface.Translate(0, rotated.Height);
surface.RotateDegrees(270);
surface.DrawBitmap(bitmap, 0, 0);
}
return rotated;
default:
return bitmap;
}
}