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Should I always downsample when loading user-saved images?

Forums > SwiftUI

My app allows users to select and save images from the Photos app.

The saved image is stored in the core data as a Binary Data type, and when I show the image, I use a GeometryReader to downsample the image to a certain size and show the image. However, I feel that the performance of the app is not good and I want to improve it, but I don't know how to improve it.

I would be grateful if you could give me some advice to improve it.

struct ContextView: View {
    @State private var seletedItem: Item?
    var body: some View {
            .sheet(item: $seletedItem) { item in
                GeometryProxy { proxy in
                    let size = proxy.size
                    DetailImageView(item: item, size: size)
                        .ignoresSafeArea(.container, edges: .top)


struct DetailImageView: View {
    var item: Item
    var size: CGSize
    private var imageHeight: CGFloat {
        size.height * 0.56
    @State private var uiImage: UIImage? = nil

    var body: some View {
        ScrollView {
            GeometryReader { proxy in
                let childSize = proxy.size
                if let uiImage {
                    Image(uiImage: uiImage)
                        .frame(width: childSize.width, height: childSize.height)
            .frame(height: size.height)
        .coordinateSpace(name: "scroll")

        .task(id: size) {
            uiImage = downsampleImage(imageData: item.imageData,
                                      to: CGSize(width: size.width, height: imageHeight))
        .onChange(of: item.unwrappedImageData) { newImageData in
            updateImage(data: newImageData, width: size.width, height: imageHeight)
        .onDisappear {
            uiImage = nil

    private func downsampleImage(imageData: Data, to pointSize: CGSize, scale: CGFloat = UIScreen.main.scale) -> UIImage {
        let imageSourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary
        guard let imageSource = CGImageSourceCreateWithData(imageData as CFData, imageSourceOptions) else { return UIImage() }

        let maxDimensionInPixels = max(pointSize.width, pointSize.height) * scale
        let downsampleOptions = [
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            kCGImageSourceShouldCacheImmediately: true,
            kCGImageSourceCreateThumbnailWithTransform: true,
            kCGImageSourceThumbnailMaxPixelSize: maxDimensionInPixels
        ] as CFDictionary

        guard let downsampledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, downsampleOptions) else { return UIImage() }
        return UIImage(cgImage: downsampledImage)


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