---
title: WWDC2001 Session 117
framework: wwdc
role: article
path: wwdc/wwdc2001-117
---

# WWDC2001 Session 117

## Transcript

Kind: captions Language: en good morning everyone I'm Travis Brown and the imaging technology manager for Mac os10 and I want to welcome you to session 117 image capture framework you've already seen image capture demonstrated on the keynote where you can take a USB digital camera plug it into a USB cable and Mac os10 will recognize that a cameras been plugged in and will then bring up a very lightweight image browser to enable the user to select which pictures they wish to download there's another dimension to image capture and that is the image capture framework underneath image capture there is a set of api's that developers can use to make their applications savvy with digital cameras so therefore you can easily take a application such as a database application where you might want to give a field that could essentially capture a camera an image off a digital camera and put that in a database that would be possible to do using the framework there's all sorts of very interesting possibilities for applications to create new features for their users in conjunction with digital cameras when the real interesting points is I want to point to some statistics is the digital camera market is exploding it's one of the fastest growing computer peripherals available and you have an interesting statistic is that you know eventually that digital cameras will fairly soon surpass that of film cameras so in terms of the way users will interact with photography and images in the future that'll very much be driven by digital cameras so it really makes sense for your applications to become aware of how to you know work with digital cameras and add value an additional interesting point that was brought up in the keynote is that of Mac users 60% of them have digital cameras and they would really love to have a seamless integration their applications with their digital cameras so now I'd like to invite Steve swin on stage to continue the presentation [Applause] Thank You Travis good morning before we start talking about image capture from Mac os10 let's review the current situation micros 9 as you know Mac OS 9 has no system level input architecture implemented so all the major device manufacturers have to do is shipping custom applications and drivers and sometimes Photoshop plug-in applications will have a hard time working with devices because doing so requires knowledge of device level communication that means you have to know how to talk to each individual device using a device protocol so image capture for Mac OS 10 what we're trying to do here is provide a device level abstraction so that would enable the applications and the device communicate through this abstraction layer very easily it's a collection of api's and setup system services like I said before enables application easy access to imaging devices such as digital camera we also provide ever a very tight system level integration to take advantage other Apple technologies such as QuickTime color sync and quartz here's a block diagram view of image capture framework to see the bottom layer darwin is the open source kernel running on top of it is the application service quartz OpenGL and QuickTime image capture framework is part of carbon library however you can access image capture directly from either carbon applications or cocoa applications there are three major components in image capture framework the first one the most critical one is the framework itself instead of api's we have a high level API for applications to use and those are low-level api for devices we also ship with building the set ability and support for cameras using standard protocols I'll get to it later we also ship image capture application which is a lightweight application to allow user to preview and download images from camera here is a another view of image capture framework you see on the left hand side you have your camera once you connect the camera to the computer image capture will load the right camera module for that device and then your application and image capture application can communicate with this camera to this device abstraction layer and using the image capture framework api's so we have a built in camera support for four different class of devices the first three are camera devices they use protocols and so you can connect the camera directly to the computer they use P DP Class D stock class and mass storage class we also support a number of removable media P DP class PD P stands for picture transfer protocol it's also known as pima 15 740 pima is the standard organization defined a standard it's an industry standard group and including platform vendors like Apple Microsoft and device manufacturers such as Kodak and Sony this protocol enables full control of camera functions so you can set the camera exposure level and you can take a picture you can retrieve picture can synchronize clock or even you you can download music files it's very powerful protocol it is transport independent the USB working group has defined the class for the PDP device already and malkos 10 10 point Oh our first implementation support a set of PDP commands that would enable you to do quote unquote plug and join operations typically you go out and take whole bunch of pictures and you come back and plug your camera into the computer we can download all the images for you recent cameras from Kodak and Sony support this protocol so if you want to get experience how this camera of PDP protocol works for you or you want to test whether your application can get one of those Kodak cameras like 4800 or mc3 or Sonya 75 there are more on the market today the second class is destock class this is a vendor specific protocol by flash point technology some Kodak and HP cameras using this protocol since it's a vendor specific protocol we rely on the device name matching to load the proper module to support your camera so if your camera uses this protocol let us know so we can add into our database third class is mass storage this is the most commonly used protocol it basically mounts the camera to storage devices as a ms-dos file flat file system on your desktop so the advantage of doing this it's a pretty simple to eat easy to implement and it's a familiar concept for users to use however the disadvantage of that is it's really the limited interface to a camera because you you the only way to control that is through file system commands so you cannot really get and set camera specific properties there's a number of removal media we can support as well compact flash smart media Memory Stick Micro Drive and the good old floppy disk super disc recordable CD this is a good way to get your image into the computer if your camera is not USB equipped or your camera protocol is currently not supported by micros 10 it's lunch you can you can take your storage device and find a card reader and plug it in and as long as you can mount your storage device on the under file system we can read it although the storage device approach is easy to implement but since we cannot treat it like a camera so we cannot ask the camera where you store your files and are you a camera device or not so we rely on a few hints first of all the device has to mount as ms-dos file system and then we search for does it have a standard DCF file structure DCF stands for digital camera file format which is defined by the standard organization if we cannot find any of this stuff and we look for is that this is one of the non-standard file structure we stored in our own database so we try to match that so if you have the file structure which is not standard not using ms-dos file system or DCF file structure or even if you do use a standard file structure but if you store the images outside the DCIM folder which is by default the folder stores still images however if you have movies and sound files stored in other folders please let us know so we can make sure we search through your folder and again like PDV camera we cannot ask the camera for image files in sound files and audio files video files so we rely on some standard file formats that we recognize to download currently mass storage interface we support JPEG TIFF and jiff for still image formats video format we support QuickTime impact and audio file format with support mp3 again if you if you store files that file type not on the list but it's important to your camera function please let us know so we can include it in the download so if your camera vendor there's three things to remember first of all use standard protocols PDP or mass storage both excellent choice you don't have to worry about getting the driver getting the support installing software user experience will be great second one is also very important send your prototypes to us to ensure compatibility it's very important senator Lee sin often sent Laura multiple copies engineers can be bribed and the last one if you have a constant file structure or a file system make sure you send us to the the the followed structure map to a silicon included in our database third part of image capture framework is image capture application this is a lightweight application to allow you to to browse and download images from camera devices and also you can define a set of hot plot actions and automatic tasks to customize your workflow we also ship a number of scripts to allow the user to do common tasks such as build web page here's the UI for image capture application the top part is camera shows you what camera device you have currently connected you can have multiple cameras connect at the same time the middle part defines Hut plot actions and automatic tasks and the last part is you specify where you want to download your files to one thing about download synchronization camera devices are increasing in resolution in an amazing rate and you can find cameras with with three four or five even six megapixels on the market today so you can imagine the file size is getting bigger and bigger so try to we try to avoid unnecessary downloads by relying on a couple of things for Mac OS 10 first of all we use file name and if we find the camera if I try to download and you have identical file name in the download folder already and those are the size of these two files in the camera and in the download folder are identical we'll skip that in the future we will use the to date in addition to file name stored metadata to do the synchronization so if your application developers make sure you do not you pre you try to preserve the metadata don't strip it out and if your camera vendors because the serial number the picture serial number is part of the file name so make sure you don't recycle the numbers and until you run out of all the combination how clock actions hot-plug action is defined to be when you connect your camera what do you want to see happen the three possibilities here the first one is when you plug in the camera we open the image capture application for you so you will see the same UI showing you earlier the user can browse and download selected and select images to download that's the default behavior or you can select automatically download all the advantage of doing that is you can automate the system when you plug in the camera there's no UI will come up all the files on the camera would be transferred to the specified download folder automatically and if you specify an automated task and that one will get invoked and all the download files will be passed to that application to do post processing one thing to point out is even if you select the default you can download come up with a UI and you can select which files you want to download and you can also specify the post processing automatic task and after downloading it will call that automatic task as well so the third action you can specify is none basically there's nothing on macros 1010 point or the first release the idea here is the user may want to use his own favorite applications to handle this camera plug-in event so we will not invoke the image capture application if you select this one and in the future to make this more useful you can actually select an application with the lunch when the hot-plug event happens and we call that application for you automatic tasks like I said before this is the post processing after you've downloaded your images you can spec you specify this automatic test and we will call it after we download all the images they can be Apple scripts applications or aliases currently you have to store these things in the library image capture scripts folder so we can pick it up in the UI we show you to which one to select in the future we're gonna put it into a preference and so you don't have to you can select it you don't have to put it into this location to get picked up so one advantage of automatic tasks is even though today not too many applications are image captured Savi when I say that it's really they don't really have the API calling API calling the image capture API to do the that stuff like getting the pictures downloaded or sending the pictures do all this stuff but however if your application can receive open events with all this files passed in and you are benefiting from image capture framework heretic because in that scenario the user can select your application it's post-processing event future directions for image capture application there are a few areas we try to improve one is made a data browser may the data is the per image information such things as exposure level your color space your creation date the size resolution and no that's good stuff and it helps the application to use the metadata down the stream to do better image management and processing we also want to improve in the browser you can do per image rotation and deletion instead of using a script you can actually wrote it in the place and delete without downloading third parties we're going to add the preference panel preference panel would allow you to select like I said before which application you want to see get lunched when you plug in a camera and those so you can specify what are the automatic tasks you want to see in your user pop-up menu couple words on scanner support for Mac OS 10 image capture would support scanner device in the future however make sure your porch your scanner to meckel's 10 today instead of waiting for image capture couple easy ways to do that first of all you can port your Mac OS 9 scanner application to two-carbon or to Mac OS 10 that's probably the least effort involved in some cases or you can support your scanner device using Twain interface and just yesterday we had this Twain announcement that Twain organization is porting Twain DSM to Mac OS 10 so if you like to use the twin interface and you can write a 20s for your scanner device and shipping that for Mac OS 10 for now and we'll figure out a way to reach the back of compatibility once we support scanner device in image capture natively so although I know that you guys probably seen image capture demo many times this week but hopefully we show you something different I want to introduce my colleague John Hagee and to come up here to give you a tour of image capture and a couple special things we did for you okay thanks Steve I'm John Maggie a lot of image capture engineers and I'm gonna give you a demo of how image capture works kind of from a user standpoint there you go just this one turned on okay I'm gonna give you a demo of how huge capture works from user standpoint and then sort of along the way show you where as a developer you can write applications that fit in it kind of one of two different places so which capture is all about connecting devices so I've got a camera here and I'm going to put it in PC connect mode and plug it in so you see the image capture app launched by itself here and like Steve was saying the reason it did that is because of the it's set to open image capture application on the hot-plug when it's plugged in so you can think of these hot plug actions as you know what happens when the camera's connected you can also think of them as how to select which files you want to download if you have application open up then the user can either download some of them or download all of them with a UI for setting preferences download all there's no UI the app doesn't come up I guess these a little progress bar with icons and the file name and the images are downloaded or none nothing happens connect the camera nothing happens so so this so again from a developer standpoint this app image capture application you could if you learn her to write an app that did something that would take the place of this application that's kind of the lowest level to to get in there and do something with the images you can use the API to get notifications of when the cameras connected and then bring up your own UI that did whatever you wanted to so that's the first place to kind of slide it in here so hot-plug actions see up the top here there's a as far as the application the we that we did to do this get a pop up of the different devices if you had multiple devices you could pick which one you wanted to download from download folders on Mac OS go ahead and show you case you don't have Mac OS 10 she should and every users home directory there's a pictures folder music folder and a movies folder so that's just there by default and although it's called image capture you know some devices also like Steve said can take pictures or store mp3s so when the image capture app it'll sort each file type in the right folder so pictures go to pictures folder movies going to movies folder and mp3s in the music folder so that's what that radio button means user can also select some other folder by clicking this button and picking a different folder so how plug actions is which files are download download folders is where they go and automatic tasks is what you want to do with the files after they've been downloaded this is pretty straightforward it's basically any app that you can drag files on to him so you know you could think you could drag an alias to Photoshop put it in this list after the images are downloaded they all open up in Photoshop or you could have something more complex that was really designed to open multiple images at the same time so we shipped a bunch of a bunch of apps that you can the user can choose from these are all Apple scripts that have been saved as applications but you could put any kind of application that accepts multiple files being dragged onto it in this list but for now I'm going to choose the format 3 by 5 and it's going to build a series of web pages with images all scale down and size to fit laid out on a page so you can print them out so I'm going to download some and pick which ones I want to ones I want to print out here there's two views there's an icon if you like this and there's a list view that gives you a little more information probably in the future it will have more of the exif data over here but for now just image and file size so I'm going to pick four of these here and actually you know let me open up the pictures folder okay just so you can see him show up so look at the icon file name progress bar now once they finish downloading it's going to launch this Apple script application and the app is going to go through with each image and figure out if it's wider than it is tall or taller than it is wide and then sort it in the in the various pages generates these web pages here so you can open this up and explore you turn off some of these extra bars here so you can think of this as being uh just a sheet of paper I picked four because you can fit four or three by 5's on a single sheet of paper if I'd selected you know six images there'd be four on this page and then two on another page so you just print out each one Explorer is really nice because they have kind of a nice print preview setup where you can adjust the settings so you print at the full size you know turnoff headers and footers and turn on print wide pages make sure the printer is turned on yes nice glossy paper so I'm using the photo paper so I'm going to go in here and set that so that it looks nice photo paper quality and hit print so that's it now what's really what's nice about Explorer is that you know even though on screen it looks like they're pretty small you know it looks like 72 dpi when it gets printed out it'll use the original image data so you're not limited to 72 dpi it'll use the full image size when it prints so you get nice high resolution photos so that's an example of you know an application that is designed to work with multiple files called from the image capture application and that's the second place that as a developer you can write apps that go in that's sort of the lighter weight you know maybe a little more user-friendly a cohesive UI for users is to write an app that deals with multiple files and have the user make an alias and put it in that scripts folder so I'll show you how that works the scripts folder is in library image capture scripts now those called scripts you memo think of it as you know applications it doesn't have to be a script it can be any kind of application and you can add to this by just making an alias and but an alias in here I've got this app called add to database that Verner wrote isn't as an example of what you might do so I'm gonna add an alias in the scripts folder and now when I launch image capture app it shows up in the pop-up here so I'm just like that and pick some more images so see when uh when the camera first when the app first launches it gets all the file names first and once they has all the file names it goes through and gets all the thumbnails so the thumbnails are actually it's not having to get the whole image file and shrink it down they're actually exif thumbnail tag inside each image so that's what's pretty quick to get the thumbnails so I'm gonna pick some images here whatever say these eight so again it's gonna download so what this application does is it works with a it works with FileMaker Pro and it adds each file to a filemaker pro database and it extracts and puts in the database the exif data that's in each image and turns out that all the images all the cameras that we've used are really great because they they put this exif data in with the image file as a user where you might not even know it's in there because a lot of apps you know don't really show that data in there but there's all kinds of good stuff in there whether the flash was turned on or not the exposure time all kinds of really useful information so this application puts that all in a database and once you have it in the database in FileMaker you can use different layouts to see as much or as little information as you want you know here's one a layout that just has the pretty basic information thumbnail date you know what kind of camera it came from the exposure and you know whether the flash was odd or not there's a another layout here that shows more information in a different view there you go so here's all the exif data that we extracted and put in this database so now it's in a database you can sort it you know you can see sorted by exposure time and figure out you know how come this picture is so blurry well because the exposure is way along that's why so that's another example of something you might want to do so here's the page that got printed out and of course you can't see it from back there but it looks pretty good so a couple of things that are kind of nice about Mac os10 from an image cache image capture standpoint is you can change the size of icons you make icons really big so like this pictures folder here so I put it in icon mode open this up and go to view options say keep range my name okay I can turn this icon size up pretty high and then just in the finder you get a nice preview of what the image looks like that's pretty convenient and then the kind of second tip but image capture is that you can customize the toolbar in Mac OS 10 do customize toolbar and you can add let's see where it is pictures there are you know buttons for your pictures folder your movies folder and your music folder so you can add that to the toolbar and then no matter where you are by clicking the pictures you can go right to your pictures folder it's kind of nice so that was an example of two applications one of them is a an Apple script that we ship users can use to print out through by 5's a second one is when the burner did that extracts the exif data listener in a in a filemaker pro database and select maybe that gives you an idea of some kind of apps you can write that that deal with multiple files so with that all handed over diverter hello my name is Ronan Northland and I'm one of the image capture engineers but now you should have a good idea about what image capture is and you actually saw it in action and so let's look at what year would have to do in order to use image capture from your application so first I'm going to talk about the application level api's that means write an application that uses image capture and get some data from a device before we actually look at the api's just a few words about the whole idea how to use it so we have an object based API which means we are dealing with objects and properties more than that later Steve was mentioning we are device independent that means whether it's a scanner or a camera scanners in the future cameras now we support it and we're transport independent so USB devices firewire devices and whatever you can think of when we talk about objects all the icao objects it's an opaque structure so you use that as reference whenever you want to access data data from the camera so objects they do have types and subtypes they basically identify the object objects can contain properties properties the ica properties that's where the actual data is stored and properties as well have types and subtypes to get identified so the symbols model is we have one object that may have another may contain another object reference another object and a property we always have a very special object at the beginning of a tree that's our device list that's always there even if you don't have a camera or other device connected you always have the device list in this case we are showing multiple devices so two cameras two scanners are connected and what will happen well if we have a closer at camera 2 you will see we have three images there and we will have some properties for the device for example the name you saw that in the image capital image capture application we had the name and an icon so the icon of course is also a property clock could be a property we could have a whole bunch of properties and that's the same thing for the images so images have properties like the image data they have a thumbnail property they have the image width and height the image name all these are properties so if you look at that tree now then you will see in order to get to the image data the only direct access point you have is the device list so from the device list you have to go to the device from the device you go to the images and from the images you go to the image data so device objects you access those via the device list the image objects via the device object and once you have device object you can iterate over all the the properties first you get the images and then iterate over all the properties to get to the actual image data all our api's have two functions two parameters they all take a parameter block and a callback a completion proc a good idea to always clear so do a mem set of the whole parameter clock fill in whatever you want to pass in to that call make the call and then depending on whether you make it a synchronous or asynchronous extract the data so that's how the napier looks like so it's an always starts with an i ca the image capture architecture and returns an OS error you pass in a parameter clock and a completion proc now for the completion clock that's how you decide how to make you what whether you want to make your calls synchronous or asynchronous if you pass in nil as completion brach then it's a synchronous call which means you make the call the camera will do whatever you tell it to do comes back and you have that the result asynchronous calls you specify your completion prog you do the image capture you call the image capture API it immediately returns and then it will call whenever the data is available from the device it will call your completion proc actually that's what we do in the image capture application so all our calls are asynchronous so the nice thing about that is you get a pretty snappy application so it's it's working the UI is updating without having the application to be multi-threaded so it's a thing of single threaded application and it still feels like yeah it's responsive so the completion proc has the single parameter and that's the ICA header that you have to typecast to whatever call result you're expecting you will have a look at that in a bit so I will go to show you how to write small image capture application and then we will look at that if you look at all our api's we can Kroop them into more or less three groups one is we have some basic functions then we have AP eyes that deal with objects and then of course the API has to deal with the properties to get to the real data so the basic functions we have very important accessor and let's get the device list so remember that was the top of the tree that's the only device that's always there even if there's no camera connected and then we have an object send message that's very useful whenever you want to send a message to for example the device like take a picture you can also send messages to image objects like delete this image object and of course what you want to do and you saw that you would see it whenever you look at the image capture application if you launch the application and no device is connected then you connect the device then it updates automatically to the UI and that's done by using the ica register event notification so you get notification once you register to that whenever device is connected or disconnected so once again the device list the ICU get device list gives you the object for the device list and you can send a message to like a device take picture the object related functions well it's quite clear when nervous look at the advice object tree you have to walk through the tree and that's basically what the device but the object related functions do so you want to find out how many children do you have for a given object so if you look at the device list in that case it would return it to meaning we have two devices connected for this second device index one so we start current with zero index one we would get back in a child count of three meaning we have three objects three images in that case as I said before each object has a type and subtype and we can get to that using the get object info so the type for the first one would be the device that's the device list and then we have the device camera device scanner and all those and for the images or sound files we would have identifier saying well it's an image it's an audio it's a it's a movie if we want to get to a specific object like in that case we already captured the device and you want to get to the second image well first of all it's a good idea to do it get a child count find out how many images to be have and if you want to iterate over all those then we would here is to get in child okay tenth child takes an index and returns you an object reference once you have an object you can always get to the top of the tree to the device list using the get device list call or you could get to the top of the device specific objects by using the get route of object that will always give you the camera device your parent of object might be useful if you have a directory structure which we're currently not supporting in our UI currently everything is flattened out also the PDP and class one drivers currently flatten out everything but in theory you could have like a directory object and all those children can access the directory object by using the get parent of object we have reference that you can set and get and then we have a whole bunch of setters and getters for properties so same deal if we have an object and we want to get the number of properties let me just do an ICA get property count that returns us the number of properties and to access the property you could do that on two ways one way would be you can iterate over all the properties so get in object as in 0 1 and so on or if you know exactly what you're looking for like in this case you could just look for the image width and instead of now looping over all properties you would just do a get property by type and pass in image width as the OS type that you're looking for you can get information about properties using get property info and you can get and set the property data in megawatts 10 1000 the set property data is not implemented but we will do that in the future so you will be able to modify properties like upload images or sound files get property get property data this call is basically the the way to get to the actual image data or thumbnail data or whatever you have stored in properties then in order to navigate around a bit again there's a get route of property which give you the device object and get pound of property that's the object that contains this property setters and getters for ref cons and now let me just switch over to the demo machine and I will show you a small application that we have to browse the property information so we have an application called image capture browser and what it does is just looking for devices objects properties in this case I was doing the get device list and then get the number of objects for that device list well we have only one so it's one camera connected so I select that camera and then you see all information flows in now this is again an example of writing it in an asynchronous mode so as you you saw just clicking on it it's really updates the UI immediately and the data that's not available just flows in whenever it gets available so that's that's the camera that John was using so with all the images again for example get the volume label so it's an HP photosmart the T is missing let's back in in the 100 versions where you have to pass in but never get to the volume label not the actual length that you have to have to increment it by one in order to get the determination so you can get the camera icon so it shows you number of bytes you can click on an image and then it will display well we have currently four properties that's the image data a thumbnail file name and file size so if I click on the file name so I would get the the name 13 bytes for that property thumbnail image data when you see this one is 145 K in size so you can just use that app to find out what's inside the camera and just look at it look at the data so now I'm just switching over to the project builder and what I am trying to do now is show you how easy it is to write an application that uses image capture so we start from scratch and we look actually I have a small application already prepared and you'll see it's almost from scratch so I switch over to the resources so it's a small cocoa application and I mean all it has is the main and then let's go to the interface builder and then well you see everything is just empty and I could now start switching over and adding an asymmetry you to do that and because what this small application should do is just capture some hits from the camera well I could do that but what I also could do is I can go to preferences and actually use the palette and that's the I see a view palette so you'll see that and all I do is I track that over I save the app I didn't change anything in here and now let's see what happens if we run this it launches and it shows the sample well actually it does more so it has a slider and we can now go through all the images that are in the device and that was without writing a lot single line of code well not quite well another thing that can do this like it allows you to track the image so whenever you are in mail you can just drag that over to mail and then insert it there so let's quit this one and let's see where the magic really lies if we go to the classes we see there's an I see a view that agent M now actually if you look at the documentation for interface builder and how to write image interface builder palettes it tells you that there are three ways to actually include the code one is in your project you just have this sources that's what I do the other one would be you just use the the pre compiled files and got all files and add those or create a small framework and use that well in this case since I want to show you how this this view actually works I was including the sources so let's go to this one and have a look at the sources if we do awake from nib that's the call actually that you will get whenever your application is launched when the nib file is loaded what I'm doing here that's a tricky thing yes I want to work or make make it work that this view actually only works in your application and not in the interface builder part so what I'm doing is if the application does not respond to one selector that I know that interface builder is using so the interface builder then I'm actually initializing the view and initializing the view is actually very simple because all I do is all I do is I call register event notification I want to get notified when a device is connected and whenever device is disconnected then oh that's that's where we are not quite to the standard so the the the best way would actually be to get the thumbnail for the thumbnail data get the size of the property that's something in the property info so you would know how big of thumbnail do I really have in that camera well in this case I know it's 128 by 128 so I'm cheating a bit and then after allocating this buffer I'm doing a rescan for devices but so let's look at it the the first part which is the event notification so what we do so we haven't I see a virtual event notification parameter Plock and as I told you the good idea to do a memset first so cleared out and then I set the refcon for the header to the self well in this case it's not needed because as you can see down here on the call itself I'm doing a synchronous call so refcon might be nice but not needed I pass in as object null which means for the event notification means notify me on all object changes so I'm not interested in a specific object at all and then the notified type that got passed in which was the device added or device removed so under just make the call and that's it now the rescan here so last thing we did in our initialization was rescan for devices risk and for devices is also pretty straightforward what it does well first if we never got initialized so remember I did not have a single line of code that I created for that project it was outside the view definition so I did not initialize the view did not do anything so what I have to do is now I have the image view that's in this nib file connected to the slider and that's what I'm doing here and then if we never did get the device list before actually then I will get it and just keep reference to it so getting the device list again I have a parameter plot that I clear and then I call get device list and do that again in a synchronous way so passing now as a completion proc so the device list will be set inside this get device list parameter block now if we did get a device list what I want to do is I want to find out how many devices are connected so I would just go ahead and pass in as the object that I'm interested in how many children's do you have that's the device list in that case so pass that in get shot count if the child can't is zero so we have no cameras connected then I just call my no device found which would just dim the slider and bring up a generic icon get in child well what I do is I want to get the first camera so this very simple app just looks at the first camera in negative zero and then tries to get the the device so if we did get the device actually first so if we have no device let me just take a predefined tip file I see a image view TIFF and just play that inside our and it's you so if we did get the if we did get a device then what we have to do is find out how many images do we have so again we have a get child count parameter clock and we clear it we set the object we are interested in to the first device and then we just call get child count so how many images or movie files do we have we get the number back save that in