Swift: resize an image is a solution? - ios

Question

I am analyzing the images captured by the camera, I am going through each pixel by pixel and storing the rgb value of each pixel in an dictionary, obviously it's taking a lot of time. Can I scale down an image without loosing the percentage of color ratio in the image...
Example: Original image has RGB color and count as
Color count
[0xF0F0F0] 100
[0xB0B0B0] 50
[0x909090] 20
Then after scaling the image by half the color count in scaled image is like this:
Color count
[0xF0F0F0] 50
[0xB0B0B0] 25
[0x909090] 10
So 2 questions:
1. Is this doable in Swift?
2. If yes, then how do I scale an image in swift

Answer 1

Scaling down an image will definitely lose some pixels.
To scale an image in Swift:
var scaledImage // your scaled-down image
var origImage // your original image
let itemSize = CGSizeMake(origImage.size.width/2, origImage.size.height/2)
UIGraphicsBeginImageContextWithOptions(itemSize, false, UIScreen.mainScreen().scale)
let imageRect = CGRectMake(0.0, 0.0, itemSize.width, itemSize.height)
origImage.drawInRect(imageRect)
scaledImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

Answer 2

This is my code for resizing a image taken by the camera, after this process I send it to our servers. I recommend it to resize it instead of eliminating colors.
Also if you don't want to resize it, you can't convert the image to JPEG and assign a quality.
Use UIImageJPEGRepresentation instead of UIImagePNGRepresentation
if let img = value as? UIImage {
var newWidth = 0
var newHeight = 0
var sizeLimit = 700 //in px
let originalWidth = Int(img.size.width)
let originalHeight = Int(img.size.height)
//Get new size with max w/h = 700
if originalWidth > originalHeight {
//Max width
newWidth = sizeLimit
newHeight = (originalHeight*sizeLimit)/originalWidth
}else{
newWidth = (originalWidth*sizeLimit)/originalHeight
newHeight = sizeLimit
}
let newSize = CGSizeMake(CGFloat(newWidth), CGFloat(newHeight))
UIGraphicsBeginImageContext(newSize)
img.drawInRect(CGRectMake(0, 0, CGFloat(newWidth), CGFloat(newHeight)))
let newImg = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
//This is a UIIMAGE
let imageData:UIImage = UIImagePNGRepresentation(newImg)
}

Answer 3

i would say this probably isnt possible, because resizing the image would change the value of the actual colours so it would give you different results.
but maybe you can look into speeding it up using the full sized image. Look into maybe using metal for GPU accelerated calculations

Answer 4

Is this doable in Swift?
Sure
If yes, then how do I scale an image in swift
If you don't mind low level functions, since this is something you want to have done fast and on the CPU, not GPU, you might want to look at the Accelerate framework and vImage_scale in particular. It provides direct access to the RGB data in memory as well.
When I did something similar in the past, I noticed that the scaling actually cuts off some colors and does not give accurate representation of the original. Unfortunately, I don't have the examples to show anymore, but I'd suggest that you try this technique with different scaling ratio to see if it gives satisfactory data in your case.

Answer 5

func scaleAndRotateImage(image: UIImage, MaxResolution iIntMaxResolution: Int) -> UIImage {
let kMaxResolution = iIntMaxResolution
let imgRef = image.cgImage!
let width: CGFloat = CGFloat(imgRef.width)
let height: CGFloat = CGFloat(imgRef.height)
var transform = CGAffineTransform.identity
var bounds = CGRect.init(x: 0, y: 0, width: width, height: height)
if Int(width) > kMaxResolution || Int(height) > kMaxResolution {
let ratio: CGFloat = width / height
if ratio > 1 {
bounds.size.width = CGFloat(kMaxResolution)
bounds.size.height = bounds.size.width / ratio
}
else {
bounds.size.height = CGFloat(kMaxResolution)
bounds.size.width = bounds.size.height * ratio
}
}
let scaleRatio: CGFloat = bounds.size.width / width
let imageSize = CGSize.init(width: CGFloat(imgRef.width), height: CGFloat(imgRef.height))
var boundHeight: CGFloat
let orient = image.imageOrientation
// The output below is limited by 1 KB.
// Please Sign Up (Free!) to remove this limitation.
switch orient {
case .up:
//EXIF = 1
transform = CGAffineTransform.identity
case .upMirrored:
//EXIF = 2
transform = CGAffineTransform.init(translationX: imageSize.width, y: 0.0)
transform = transform.scaledBy(x: -1.0, y: 1.0)
case .down:
//EXIF = 3
transform = CGAffineTransform.init(translationX: imageSize.width, y: imageSize.height)
transform = transform.rotated(by: CGFloat(Double.pi / 2))
case .downMirrored:
//EXIF = 4
transform = CGAffineTransform.init(translationX: 0.0, y: imageSize.height)
transform = transform.scaledBy(x: 1.0, y: -1.0)
case .leftMirrored:
//EXIF = 5
boundHeight = bounds.size.height
bounds.size.height = bounds.size.width
bounds.size.width = boundHeight
transform = CGAffineTransform.init(translationX: imageSize.height, y: imageSize.width)
transform = transform.scaledBy(x: -1.0, y: 1.0)
transform = transform.rotated(by: CGFloat(Double.pi / 2) / 2.0)
break
default: print("Error in processing image")
}
UIGraphicsBeginImageContext(bounds.size)
let context = UIGraphicsGetCurrentContext()
if orient == .right || orient == .left {
context?.scaleBy(x: -scaleRatio, y: scaleRatio)
context?.translateBy(x: -height, y: 0)
}
else {
context?.scaleBy(x: scaleRatio, y: -scaleRatio)
context?.translateBy(x: 0, y: -height)
}
context?.concatenate(transform)
context?.draw(imgRef, in: CGRect.init(x: 0, y: 0, width: width, height: height))
let imageCopy = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return imageCopy!
}