fix: use createBackupCGContext in cgImageWithFixedOrientation (#414)

convert 10-bit image to 16-bit image to preserve accuracy
guoyingtao · Oct 13, 2024 · 3430aaf · 3430aaf
1 parent 40ad916
commit 3430aaf
Show file tree

Hide file tree

Showing 3 changed files with 42 additions and 16 deletions.
diff --git a/Example/MantisExample.xcodeproj/xcshareddata/xcschemes/MantisExample.xcscheme b/Example/MantisExample.xcodeproj/xcshareddata/xcschemes/MantisExample.xcscheme
@@ -51,6 +51,13 @@
             ReferencedContainer = "container:MantisExample.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
+      <EnvironmentVariables>
+         <EnvironmentVariable
+            key = "CGBITMAP_CONTEXT_LOG_ERRORS"
+            value = "1"
+            isEnabled = "YES">
+         </EnvironmentVariable>
+      </EnvironmentVariables>
    </LaunchAction>
    <ProfileAction
       buildConfiguration = "Release"

diff --git a/Sources/Mantis/Extensions/CGImageExtensions.swift b/Sources/Mantis/Extensions/CGImageExtensions.swift
@@ -52,13 +52,7 @@ extension CGImage {
                                 space: colorSpaceRef,
                                 bitmapInfo: bitmapInfoData)
         ??
-        CGContext(data: nil,
-                  width: Int(round(outputSize.width)),
-                  height: Int(round(outputSize.height)),
-                  bitsPerComponent: bitsPerComponent,
-                  bytesPerRow: bitmapBytesPerRow,
-                  space: colorSpaceRef,
-                  bitmapInfo: getBackupBitmapInfo(colorSpaceRef))
+        createBackupCGContext(size: outputSize, bitmapBytesPerRow: bitsPerComponent, colorSpaceRef: colorSpaceRef)
 
         guard let context = context else {
             throw ImageProcessError.failedToBuildContext(colorSpaceModel: colorSpaceRef.model,
@@ -86,6 +80,29 @@ extension CGImage {
         return context.makeImage()
     }
 
+    func createBackupCGContext(size: CGSize,
+                               bitmapBytesPerRow: Int = 0,
+                               colorSpaceRef: CGColorSpace) -> CGContext? {
+        var actualBitsPerComponent = bitsPerComponent
+        var actualBitmapBytesPerRow = bitmapBytesPerRow
+
+        /* Convert a 10-bit image to a 16-bit image to preserve accuracy.
+        Since we haven't successfully created a 10-bit image CGContext yet, we're temporarily using this method.
+         */
+        if (32, 10) == (bitsPerPixel, bitsPerComponent) {
+            actualBitsPerComponent = 16
+            actualBitmapBytesPerRow = Int(round(size.width)) * 8
+        }
+
+        return CGContext(data: nil,
+                         width: Int(round(size.width)),
+                         height: Int(round(size.height)),
+                         bitsPerComponent: actualBitsPerComponent,
+                         bytesPerRow: actualBitmapBytesPerRow,
+                         space: colorSpaceRef,
+                         bitmapInfo: getBackupBitmapInfo(colorSpaceRef))
+    }
+
     /**
      Just in case the bitmapInfo from original image is not supported by CGContext, we will use this backup bitmapInfo instead.
      */
@@ -100,11 +117,7 @@ extension CGImage {
             case (32, 8), (64, 16):
                 return CGImageAlphaInfo.premultipliedLast.rawValue
             case (32, 10):
-                if #available(iOS 12, macOS 10.14, *) {
-                    return CGImageAlphaInfo.alphaOnly.rawValue | CGImagePixelFormatInfo.RGBCIF10.rawValue
-                } else {
-                    break
-                }
+                return CGImageAlphaInfo.premultipliedLast.rawValue
             case (128, 32):
                 return CGImageAlphaInfo.premultipliedLast.rawValue | (bitmapInfo.rawValue & CGBitmapInfo.floatComponents.rawValue)
             default:

diff --git a/Sources/Mantis/Extensions/UIImageExtensions.swift b/Sources/Mantis/Extensions/UIImageExtensions.swift
@@ -12,7 +12,7 @@ extension UIImage {
         if imageOrientation == .up {
             return cgImage
         }
-
+        
         guard let cgImage = cgImage, let colorSpace = cgImage.colorSpace else {
             return nil
         }
@@ -49,16 +49,22 @@ extension UIImage {
             break
         }
 
-        guard let context = CGContext(
+        var context = CGContext(
             data: nil,
             width: Int(width),
             height: Int(height),
             bitsPerComponent: cgImage.bitsPerComponent,
             bytesPerRow: 0,
             space: colorSpace,
             bitmapInfo: UInt32(cgImage.bitmapInfo.rawValue)
-            ) else {
-                return nil
+            )
+
+        if context == nil {
+            context = cgImage.createBackupCGContext(size: size, bitmapBytesPerRow: 0, colorSpaceRef: colorSpace)
+        }
+
+        guard let context else {
+            return nil
         }
 
         context.concatenate(transform)