Sd Memory Cards

[Scylax]

I am constantly being surprised by the efficiency of technological innovations, but what really staggers my comprehension is how a tiny card in a digital camera can hold many hundreds of immensely detailed pictures.

To me, it's not just clever, it's almost magic. How is it done ? I realize that this is a simple question with a far from simple answer, but can anyone try to enlighten me, please?

[VHG]

More and more information is held in DIGITAL format. This includes digital photos, audio CDS, DVDs, mobile phones, and everything on your computer.

Digital format consists basically of storing EVERYTNING in strings of zeroes (0) and ones (1).

So a digital photo, looked at digitally, may look like this:

0011 1110 0111 0011 1001 and so on for MILLIONS of characters.

When your camera or computer looks at these zeros and ones it then converts it into your digital picture.

Your CD player converts zeroes and ones into songs, your DVD player converts zeroes and ones into a movie, your mobile phone converts zeroes and one into someone's voice and so on.

Storing just zeroes and ones is fairly simple and over the years they have managed to squeeze the amount of zeros and ones they can store into smaller and smaller sizes so now an SD card can hold thousands of digital photos.

[VHG]

It should be noted of course that each device creates these zeros and one in a different way.

So your camera for example divides a photo up into very very small squares called pixels. There are millions of pixels in a single photo.

When you take a photo, for each pixel the camera measures the strength of each of three colours - Red, Green, and Blue. It uses a number between 0 and 255.

So a single pixel may be red - 20, blue - 70, green - 187. When these colour strengths are merged together they make the right colour for that single pixel.

One photograph can consist of millions of pixels (a camera is measured in megapixels) and when you take a photo the camera makes note of the strength of red/green/blue for each pixel.

So the camera is not actually saving the picture as a picture, but as a string of numbers. So 20,70,187 for the first pixel, 200, 150, 12 for the second pixel and so on.

When it comes to save the "photo" onto the SD card it converts those DECIMAL numbers 20,70,187 etc) into BINARY numbers (0 and 1).

So your digital photo is now saved on your SD card as millions of zeroes and ones. There will be a set of zeroes and ones at the start to identify it as a digital photo and not a video file or audio track.

When your camera or computer wants to display the picture it uses a reverse process to convert these zeros and ones back into a picture.

[Old_Geezer]

It is done by having loads of locations which can store binary information. Typically a voltage is stored at each location. A positive voltage for a binary 1 and zero for a binary 0. Each are very small physically which is why so much gets stored on a small card: enough for loads of pictures for example.

[ck1]

VHG - that makes a lot of sense with regards to the photos (never understood that!), how about music though, with so many different sounds etc how are they converted to binary? What distinguishes a drum beat from a guitar?

[Old_Geezer]

The way the data changes over time.

[Scylax]

VHG: my gratitude for your precise, and concise answer(s). It's still magic to me, but understandable magic.. Your explanation for voice and music was a bonus too. Now the light shines, and the tunnel is not so dark...

[ToraToraTora]

then of course there are compression algorithms, so take the 0 and 1's from VHG's explanation and organise them into bytes, groups of eight, then with pictures and music you will find that there is repetition, ie most pictures have a lot of the same colour contiguously eg the sky for example so now you may have a thousand bytes all the same colour so now you don't need to store 1000 of the same you can store it in much less eg repetition factor code, then the factor then the subject. so you can get 1000 bytes into 4 now. So space is optimised, the photo is expanded on retrieval and you are none the wiser.

[jno]

granted the principle of digitisation, how is it that a card that used to store half a gigabyte of memory or less now holds 16GB? Is this due to different materials or more efficient ways of compression or what?

[ToraToraTora]

it's the hardware jno, ever more capacity with the materials concerned. I have little understanding of the structure but these storaqge media are getting ever closer to storage at the atomic level, currently not far off molecular level. Compression algorithms are nothing new.

[wildwood]

jno, there are now micro SD card that can hold 64GB. It is almost beyond belief.

[Scylax]

Wildwood: 64 GB. is, I agree, almost beyond belief. It is certainly beyond comprehension. We can't envisage billions. As for trillions, well, a trillion seconds ago it was c.30,000 B.C.

How long before we have SD cards of 128GB ?

[Zacs-Master]

Syclax - Google Moore's law.

[society]

128 gb cards do exists - http://tinyurl.com/nzcjve3

[jno]

thanks, TTT.

128GB; gee.

But I'm told the computers that took Neil Armstrong to the moon had less power than a digital watch.