Pixel Array to UIImage in Swift - ios

Question

I've been trying to figure out how to convert an array of rgb pixel data to a UIImage in Swift.
I'm keeping the rgb data per pixel in a simple struct:
public struct PixelData {
var a: Int
var r: Int
var g: Int
var b: Int
}
I've made my way to the following function, but the resulting image is incorrect:
func imageFromARGB32Bitmap(pixels:[PixelData], width: Int, height: Int)-> UIImage {
let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo:CGBitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedFirst.rawValue)
let bitsPerComponent:Int = 8
let bitsPerPixel:Int = 32
assert(pixels.count == Int(width * height))
var data = pixels // Copy to mutable []
let providerRef = CGDataProviderCreateWithCFData(
NSData(bytes: &data, length: data.count * sizeof(PixelData))
)
let cgim = CGImageCreate(
width,
height,
bitsPerComponent,
bitsPerPixel,
width * Int(sizeof(PixelData)),
rgbColorSpace,
bitmapInfo,
providerRef,
nil,
true,
kCGRenderingIntentDefault
)
return UIImage(CGImage: cgim)!
}
Any tips or pointers on how to properly convert an rgb array to an UIImage?

Answer 1

Note: This is a solution for iOS creating a UIImage. For a solution for macOS and NSImage, see this answer.
Your only problem is that the data types in your PixelData structure need to be UInt8. I created a test image in a Playground with the following:
public struct PixelData {
var a: UInt8
var r: UInt8
var g: UInt8
var b: UInt8
}
var pixels = [PixelData]()
let red = PixelData(a: 255, r: 255, g: 0, b: 0)
let green = PixelData(a: 255, r: 0, g: 255, b: 0)
let blue = PixelData(a: 255, r: 0, g: 0, b: 255)
for _ in 1...300 {
pixels.append(red)
}
for _ in 1...300 {
pixels.append(green)
}
for _ in 1...300 {
pixels.append(blue)
}
let image = imageFromARGB32Bitmap(pixels: pixels, width: 30, height: 30)
Update for Swift 4:
I updated imageFromARGB32Bitmap to work with Swift 4. The function now returns a UIImage? and guard is used to return nil if anything goes wrong.
func imageFromARGB32Bitmap(pixels: [PixelData], width: Int, height: Int) -> UIImage? {
guard width > 0 && height > 0 else { return nil }
guard pixels.count == width * height else { return nil }
let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue)
let bitsPerComponent = 8
let bitsPerPixel = 32
var data = pixels // Copy to mutable []
guard let providerRef = CGDataProvider(data: NSData(bytes: &data,
length: data.count * MemoryLayout<PixelData>.size)
)
else { return nil }
guard let cgim = CGImage(
width: width,
height: height,
bitsPerComponent: bitsPerComponent,
bitsPerPixel: bitsPerPixel,
bytesPerRow: width * MemoryLayout<PixelData>.size,
space: rgbColorSpace,
bitmapInfo: bitmapInfo,
provider: providerRef,
decode: nil,
shouldInterpolate: true,
intent: .defaultIntent
)
else { return nil }
return UIImage(cgImage: cgim)
}
Making it a convenience initializer for UIImage:
This function works well as a convenience initializer for UIImage. Here is the implementation:
extension UIImage {
convenience init?(pixels: [PixelData], width: Int, height: Int) {
guard width > 0 && height > 0, pixels.count == width * height else { return nil }
var data = pixels
guard let providerRef = CGDataProvider(data: Data(bytes: &data, count: data.count * MemoryLayout<PixelData>.size) as CFData)
else { return nil }
guard let cgim = CGImage(
width: width,
height: height,
bitsPerComponent: 8,
bitsPerPixel: 32,
bytesPerRow: width * MemoryLayout<PixelData>.size,
space: CGColorSpaceCreateDeviceRGB(),
bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue),
provider: providerRef,
decode: nil,
shouldInterpolate: true,
intent: .defaultIntent)
else { return nil }
self.init(cgImage: cgim)
}
}
Here is an example of its usage:
// Generate a 500x500 image of randomly colored pixels
let height = 500
let width = 500
var pixels: [PixelData] = .init(repeating: .init(a: 0, r: 0, g: 0, b: 0), count: width * height)
for index in pixels.indices {
pixels[index].a = 255
pixels[index].r = .random(in: 0...255)
pixels[index].g = .random(in: 0...255)
pixels[index].b = .random(in: 0...255)
}
let image = UIImage(pixels: pixels, width: width, height: height)

Answer 2

Update for Swift 3
struct PixelData {
var a: UInt8 = 0
var r: UInt8 = 0
var g: UInt8 = 0
var b: UInt8 = 0
}
func imageFromBitmap(pixels: [PixelData], width: Int, height: Int) -> UIImage? {
assert(width > 0)
assert(height > 0)
let pixelDataSize = MemoryLayout<PixelData>.size
assert(pixelDataSize == 4)
assert(pixels.count == Int(width * height))
let data: Data = pixels.withUnsafeBufferPointer {
return Data(buffer: $0)
}
let cfdata = NSData(data: data) as CFData
let provider: CGDataProvider! = CGDataProvider(data: cfdata)
if provider == nil {
print("CGDataProvider is not supposed to be nil")
return nil
}
let cgimage: CGImage! = CGImage(
width: width,
height: height,
bitsPerComponent: 8,
bitsPerPixel: 32,
bytesPerRow: width * pixelDataSize,
space: CGColorSpaceCreateDeviceRGB(),
bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue),
provider: provider,
decode: nil,
shouldInterpolate: true,
intent: .defaultIntent
)
if cgimage == nil {
print("CGImage is not supposed to be nil")
return nil
}
return UIImage(cgImage: cgimage)
}