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Saturday, November 10, 2012

iPhone 4: Stay away from CameraTweak's 30+ fps mode in 720p!

Today, I (finally) had some time to thoroughly test how the excellent Cydia tweak "CameraTweak" runs on the iPhone 4. (Dedicated, earlier review with thorough iPhone 3G S, 4S and iPod touch 4 tests HERE)

As with the earlier-tested models (iPhone 3G S, 4S and iPod touch 4), the still shooting tweaks (one-shot timer mode; making a shot every second after a settable timeout; locking the white balance / setting the exposure independent of the focus point etc.) all worked just fine.

As with the earlier-tested iDevices, it is  video (as opposed to stills shooting) recording where differences and sometimes unwanted side effects happen. First, let's take a look at the behavior that was easy to predict based on my earlier experiences with directly tweaking the camera:

- you can't record with more than 30 fps at any resolution (tested with all)

- lower FPS speeds all worked at the native 720p (haven't tested this with lower resolutions), as opposed to the 4S, which had problems with FPS settings between 2 and 14 in the (native) 1080p mode. (On the 4S, other custom framerates under 30 worked as expected.).

And for something not (necessarily) spotted by casual users: the disadvantage of setting a higher (anything over 30) framerate at 720p to achieve a much wider field-of-view.

Let me show you a frame grab shot at the default 720p mode, without any tweaks:

(as with most images in this article, click it for the original, much bigger one. You will want to do this particularly with shots demonstrating the resolution differences between the different video shooting modes - they're absolutely impossible to assess on a high-compression, low-resolution thumbnail.)

Now, let's activate any fps over 30 using the framerate setter tweak:

(Here, I've set it to 50. (It could have been anything over 30, even 31.) Don't forget to tap the "SET" button after setting the framerate! Note that it, generally, doesn't work in Landscape mode; that is, rotate your phone to Portrait mode before trying to tap it! Also note that the shot shows both the focus (top right) and exposure (top left) setters as I've enabled advanced mode by tapping the leftmost icon on the bottom left.)

Look at what happened to the field-of-view! I haven't moved the iPhone a bit from its earlier position (from where I've taken the default 720p shot):

Yes - the FoV has become much-much wider, which means fixing one of the biggest problems (namely, the too-narrow FoV in video mode common with all iPhone models starting with iPhone 4) of the iPhone 4.

However, if you take a closer look at the original image (again: don't forget to click the thumbnail for the original frame grab!), you'll notice the following:

- while the recorded video has the aspect ratio of 16:9 (physically, it's recorded as a 1280*720 stream), it compresses the original image vertically; this is why the 16:9 resolution chart just fills out the entire frame horizontally, while, vertically, a lot other areas are also shot. This is, however, only the slighter problem:

- the resolution of the tweaked mode is far inferior to that of the standard 720p - or, for that matter, the VGA (640*480)-resolution mode. Here's a shot of the 720p (showing pretty similar results to my original, iPhone 4 resolution-related article BTW) resolution of the same iPhone, under exactly the same circumstances (lighting etc.):

And here's the VGA resolution (same iPhone 4, same environment):

As you can see, even the VGA-resolution footage offers far superior resolution than the "tweaked" 720p mode. In addition, when shooting using VGA resolution, the FoV also becomes much wider than in the native 720p mode. As is, incidentally, the case with the iPhone 4S as well (1080p vs. 720p vs. VGA FoV comparison shots HERE)

All in all,

in any mode, don't ever try increasing the framerate over 30! (Decreasing works, on the other hand, just fine.) As I've just shown you, the much wider FoV also introduces severe problems - most importantly, vastly decreased true resolution.

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