Category Archives: IPod-touch

iPhone 4S WiFi grayed out. Let’s fix it.

Recently, my iPhone (iOS 7.1.1) 4S’s WiFi module has been disabled for some reasons. I couldn’t remember exactly what happened but I think the WiFi module went out while switching Airplane-mode.

Anyway after this thing happened, WiFi enable button always grayed out and I can’t enable it.

After googling, an interesting way might can resolve the issue at least my case. The steps are simple: 1) Using a hair dryer or a heat-gun, make your iPhone detect over-temperature. 2) Turn it off and put it in the freezer for 10 minutes. 3) Turn it on and check it whether it works or not.

It seems that the power manager of the iPhone is forced to be hardware-reseted when it detects over-temperature for safety reason. (There is a quite big LiPo in the phone)

Some forks said that it only worked for a couple of days but I don’t know how it will work for me.

The following youtube video shows procedures described above.

Good luck.

AE/AF lock on the iPhone.

By default, AE/AF is enabled on the iPhone. These features are useful for obtaining sort of “Good looking images”. Sometime however, you might want to use your iPhone for other scientific purposes since it is in your pocket! Then these AE/AF function makes your algorithm or other software packages mass up quite easily.

There is a very simple solution to disable these features. All what you need to do is simply holding on the screen after launching the camera application. Then you can see “AE/AF lock” on your bottom of screen. Apple says  it works iPhone3GS/higher with iOS5/higher.

More information can be found:

Apple iPhone 4 camera specs

On 2010, June 7 His Steveness has introduced the Apple iPhone 4 which features a new camera module. Two actually but I am going to talk about the main camera (on its rear side) only. And only about its still photography capabilities (it records 720p 30fps HD video as well).

It is typically hard to figure out the exact camera specification for cell phones and to compare them with a P&S camera. E.g., the HTC EVO 4G is said to have an 8 megapixel camera but little else is known. Images shot with the EVO all lack the significant EXIF information!

However, I think I managed to extract the full iPhone 4 camera specs now.

First, the pixels are 1.75 µm (according to Job’s keynote) and we may assume that this is the pixel pitch. Sample images are 2592×1936 pixels (5.0 MP, 4.02:3). This makes a 4.54 x 3.39 mm^2 chip (5.67 mm diagonal) which corresponds to a 35mm film camera crop factor of 7.64.

In a P&S, this would be called a 1/3.2″ sensor and P&S sensors range between 1/3.8″ and 1/1.5″ (crop factors between 8.6 and 3.9). So, it is an imaging sensor at the lower end of the P&S range, but it is in the P&S range and with a reasonable number of pixels and a back-illuminated sensor like the Sony Exmor R sensor. Here is a sample image from Apple’s web site:

(click on the image for the sample in original size; hosted on has published the full EXIF data for exactly this sample photo (it is magically absent from the web sample though …):

Aperture: 2.97
Color space: Uncalibrated
Date and time: 2010/05/07 15:14
Exposure: Auto exposure
Exposure time: 1/887
Flash: Flash did not fire, auto mode
FNumber: 2.8
Focal length: 3.85
ISO speed rating: 80
Metering mode: Spot
Sharpness: Hard
White balance: Auto

So, the lens is a 3.85 mm f/2.8 lens.

This corresponds to 35mm film camera equivalent lens of 29.4mm f/21.4.

I should note that even an aperture this small is not restricted by diffraction yet (limit at f/2.8 is at 54% of pixel width). This is a good value. But one really shouldn’t stop down beyond f/4 and it seems the iPhone 4 has an f/3 fixed aperture lens anyway.


iPhone 4 main camera:

  • 5.0 Mpixels (2592 x 1936)
  • 1/3.2″ back-illuminated CMOS sensor
  • 4:3 aspect ratio
  • 35 mm film camera crop factor: 7.64
  • Low ISO 80 (or better)
  • 3.85 mm lens focal length
  • f/2.8 lens aperture
  • Autofocus: tap to focus

Equivalent 35mm film camera and lens:

  • 30 mm f/22

So, don’t throw away your FourThird, APS-C or full frame SLR ;)

Besides the deep depth of field, an f/21.4 aperture at ISO 80 produces as much noise as an f/8 lens at ISO 570 (for a given shutter speed). Where 35mm film camera f/8 and APS-C f/5.6 produce the same level of noise.


The iPhone 4 seems to have a camera which should deliver an image quality on par with the lower segment of P&S cameras. It’s field of view (no zoom!) corresponds to a 30mm lens (on a 35mm film camera) and it captures as much light (produces as much noise) as a system camera with a lens aperture between f/11 (FourThird) and f/22 (35mm film).