ios - CGImageCreateWithImageInRect subimages are zoomed and misplaced -

i want experiment real-time filtering of subregions of iphone camera feed. idea display filtered regions overlaid on screen can see filtering results in real-time move camera.

it seems should straightforward extract frame subimages via cgimagecreatewithimageinrect , put them in uiimageviews. resulting images zoomed , misplaced, , i'm lost why.

here's app running. note subimages zoomed , not aligned guide boxes

i've looked through many, many posts , blogs, , closest i've found problem in post:

cannot crop touched location cgimagecreatewithimageinrect in swift

but solution relies on features of uiimageview source, uiview , avcapturevideopreviewlayer i'm using don't have. , it's not clear me why fix works in case.

my code obtains preview frames pixel buffers via avcapturevideodataoutputsamplebufferdelegate : captureoutput : didoutputsamplebuffer , converts them cgimages input cgimagecreatewithimageinrect. rect parameters use guide boxes' uiview.frame members.

here's app in ib. each uiimageview constrained same dimensions corresponding uiview (i.e. guide box).

here's source:

import uikit import avfoundation  class viewcontroller: uiviewcontroller, avcapturevideodataoutputsamplebufferdelegate {  @iboutlet weak var previewview: uiview!  @iboutlet weak var datetimecapture: uiimageview! @iboutlet weak var machineidamttime: uiimageview! @iboutlet weak var ticketid: uiimageview!  @iboutlet weak var datetimecapturebox: uiview! @iboutlet weak var machineidamttimecapturebox: uiview! @iboutlet weak var ticketidcapturebox: uiview!  var convertctx: cicontext? var capturesession: avcapturesession? var stillimageoutput: avcapturestillimageoutput? var previewlayer: avcapturevideopreviewlayer? var overlaylayer: calayer?  override func viewdidload() {     super.viewdidload()      convertctx = cicontext(options: nil)      // guide boxes set black in ib can see them     // clear them here     datetimecapturebox.backgroundcolor = uicolor.clearcolor()     machineidamttimecapturebox.backgroundcolor = uicolor.clearcolor()     ticketidcapturebox.backgroundcolor = uicolor.clearcolor()      // set color bright green , border useful width     datetimecapturebox.layer.bordercolor = uicolor.greencolor().cgcolor     datetimecapturebox.layer.borderwidth = 5      machineidamttimecapturebox.layer.bordercolor = uicolor.greencolor().cgcolor     machineidamttimecapturebox.layer.borderwidth = 5      ticketidcapturebox.layer.bordercolor = uicolor.greencolor().cgcolor     ticketidcapturebox.layer.borderwidth = 5 }  override func viewwillappear(animated: bool) {     super.viewwillappear(animated)      capturesession = avcapturesession()     capturesession!.sessionpreset = avcapturesessionpresetphoto      let backcamera = avcapturedevice.defaultdevicewithmediatype(avmediatypevideo)      var error: nserror?     var input: avcapturedeviceinput!     {         input = try avcapturedeviceinput(device: backcamera)     } catch let error1 nserror {         error = error1         input = nil     }      if error == nil && capturesession!.canaddinput(input) {         capturesession!.addinput(input)          stillimageoutput = avcapturestillimageoutput()         stillimageoutput!.outputsettings = [avvideocodeckey: avvideocodecjpeg]         if capturesession!.canaddoutput(stillimageoutput) {             capturesession!.addoutput(stillimageoutput)              previewlayer = avcapturevideopreviewlayer(session: capturesession)             previewlayer!.videogravity = avlayervideogravityresizeaspect             previewlayer!.connection?.videoorientation = avcapturevideoorientation.portrait             previewview!.layer.addsublayer(previewlayer!)              capturesession!.startrunning()         }     }      let videooutput = avcapturevideodataoutput()      videooutput.setsamplebufferdelegate(self, queue: dispatch_get_main_queue())      if capturesession!.canaddoutput(videooutput)     {         capturesession!.addoutput(videooutput)         videooutput.connectionwithmediatype(avmediatypevideo).videoorientation = avcapturevideoorientation.portrait         videooutput.connectionwithmediatype(avmediatypevideo).videoscaleandcropfactor = 1.0     }  }  override func viewdidappear(animated: bool) {     super.viewdidappear(animated)     previewlayer!.frame = previewview.bounds }  func captureoutput(captureoutput: avcaptureoutput!, didoutputsamplebuffer samplebuffer: cmsamplebuffer!, fromconnection connection: avcaptureconnection!) {     // 1. image data cmsamplebuffer cvpixelbuffer     let pixelbuffer = cmsamplebuffergetimagebuffer(samplebuffer)      // 2. ciimage can cgimage     //    need in order extract rectangular subimage     //    via cgimagecreatewithimageinrect     let cameraciimage = ciimage(cvpixelbuffer: pixelbuffer!)      // 3. cgimage     let cameracgimage = convertciimagetocgimage(cameraciimage)      self.datetimecapture.image = uiimage(cgimage: cgimagecreatewithimageinrect(cameracgimage, datetimecapturebox.frame)!)      self.machineidamttime.image = uiimage(cgimage: cgimagecreatewithimageinrect(cameracgimage, machineidamttimecapturebox.frame)!)      self.ticketid.image = uiimage(cgimage: cgimagecreatewithimageinrect(cameracgimage, ticketidcapturebox.frame)!)  }  func convertciimagetocgimage(inputimage: ciimage) -> cgimage! {     return convertctx!.createcgimage(inputimage, fromrect: inputimage.extent) }  func captureoutput(captureoutput: avcaptureoutput!, diddropsamplebuffer samplebuffer: cmsamplebuffer!, fromconnection connection: avcaptureconnection!) {    // print("drop") }   }