Actually the capture is at a higher bit rate: 12, 14 or 16 bit per
colour depending on the camera
i
Sent from my iPhone
On 13 May 2010, at 07:14, karl shah-jenner <shahjen@xxxxxxxxxxxx> wrote:
Kosas writes:
Kostas Papakotas hi all!
this I noticed soem time ago in my Pentax K10D.....
took a scene in 10MB and 6MB.....pxel count was
10Mp - Raw - 12359 KB
06Mp - Raw - 11479 KB
10Mp - JPG - 3069 KB
06Mp - JPG - 1707 KB
**********************************
Kostas, I believe the pixel count for the 10Mp is 3872 x 2592 (10.0
MP) - that is the total number of sensors on the array, the number
of squares in the grid that makes up the image. ten million squares.
Each pixel/square/grid element is made up of 3 bytes of data for a
24 bit colour image (which is 8 bits, or 256 shades per colour, 3
colours = 24) , so there really should be 10 million pixels x 3
bytes per pixel = 30 million bytes of data (26Mb)
But there isn't 24 bit colour off the sensor, it's only 1 byte as
each sensor is actually monochromatic with a filter on top of it..
So REALLY there's 10.0Mp x 1 byte = 10Mb (actually it's 9.57
megabytes of data)
Actually to be honest, before image capture there's just a bunch of
analogue values at each photoreceptor site.. when these go through
the analogue>digital converter that's when we get data.
RAW is kind of proprietry and adds some of the information the
camera thinks is important - basically it's a data grab of the
mosaic of monochrome values BUT they're also tagged for the colour
filter that sits on top of the photosite - so that's more data added
to the monochrome values. Being RAW it should grab *all* the
information the sensor is capable of, so that's the full frame. No
such thing as interpolating down to 6, 3 or 1Mp.. it's just a full
grab. so in theory we should get precisely the same amount of data
(9.57Mb+ other stuff) for each and every shot, irrespective of the
subject
When it comes to jpeg, and dont forget jpeg is a compression
algorithm like zip, it is not an image format (however it is
exclusively used for 'zipping' bitmapped images) - the megapixel
count you set is taken into account and data is dumped.
A jpeg, depending on the compression, can allow a lot or a little
bit or no data to be discarded from the bitmap, depending on the
image. For example, a fully overexposed shot should be much smaller
in disk size (kb) where it is basically a whole white image, than
say a landscape with many colour values and location. really it's
just saying "one white pixel x 10 million of them thanks!"
I just made a 4x5 pixel image and saved it to my desktop at 50% and
100% jpeg quality - they are both 346 bytes in size. I resized them
both to 1280x1600 pixels, when opened they form a bitmap taking up
5.68Mb of memory, but compressed as they are, they only take up 12kb
of disk space, both exactly the same, 50 and 100% quality.
an image of a butterfly I have sized also to 1280x1600 by comparison
takes up 1.33Mb on my drive, but decompressed (inflated to it's
bitmap) takes up 5.86 Mb of ram
As you can see, the bitmapped image of a pure white square and a
complicated image are exactly the same when they are open. It
*should* be the same for RAW files.
but each manufacturer choses to implement RAW differently so what
data they include or exclude is pretty mcuh going to remain a
mystery, and that's why you're seeing only a slight difference.
..which is pretty much what Herschel said .. I just made it more
complicated ;)
karl
