I'm sure this has been asked here before, but I'm new here.... not new to photography, digital or film but still confused.
I purchased a Nikon D7000 recently... every place I look the specifications say this is a 16.2 mega pixel camera.... when I take a picture in the RAW format with the camera the mega pixel size of the file is right around 23 or 24.... what gives? Of course the jpeg files are around half of the 16.2... 8 or 9....
< the specifications say this is a 16.2 mega pixel camera > So far, so good!
<< when I take a picture in the RAW format with the camera the mega pixel size of the file is right around 23 or 24 >>
There it is! Ok, let's see
"16.2 mega pixel" is clear, it is the resolution.
When the camera takes a shot, it will record the info of you picture on the memory media you put in your body. Your camera will not save a picture on the card but will write data. This amount of data for each file represents all the info relative to the picture you just took plus the metadata you have chosen to be included.
On this card, as well as on your computer, data files are measured in megabytes, MB.
Megabytes MB, megapixels MP… huh? now you got it!
Your camera has a sensor of 16,2 MP and record files that are 23-24 MB in the case of your RAW files. Da,Da!
Each pixel in your raw image is represented by a 2 byte integer. At 4928x3264 pixels, this gives 4928x3264x2 = 32169984 = 30.6 MB where a megabyte is actually (1024*1024=1,048,576) bytes. The D7000 raw format is a compressed format, so these 30.6 megabytes of data are compressed down to about 23-24 megabytes on your card.
To further confuse the issue, A megapixel is 1,000,000 pixels. The reason a megabyte is 1024*1024=1,048,576 is due to the way software developers think about memory and numbers and the fact that this is an even power of 2. Camera manufacturers like to use 1,000,000 pixels to mean a megapixel because it lets them put slightly larger numbers in their marketing literature. You D7000 is marketed as a 16.2 megapixel camera. If it were calculated the same way as megabytes are, it would only be 15.3 megapixels. Note: in recent years, hard drive manufacturers have taken to using 1,000,000 bytes as a megabyte for the same marketing reasons
Thu 09-May-13 09:45 AM | edited Thu 09-May-13 09:51 AM by PAStime
While we are at it, I believe there are a relatively small number of pixels around the periphery of the sensor which are used to assess on-chip sensor noise but are not used in the final image. The information is used in the in-camera processing of the image. I recall reading once that sensor suppliers sometimes include these pixels in the pixel count, or sometimes say "approximately x pixels".
I'm looking at the Sony spec sheet for the sensor that is my D90. It lists three numbers: total number of pixels, number of effective pixels, and number of active pixels. The numbers are 13.05M, 12.47M, and 12.41M, respectively.
Peter, I believe you're right that there is a masked area around the perimeter used as a black reference. I also believed there is a perimeter of pixels that are used for interpolation data in the demosaic process that is also not used in the image. But I believe other converters such as dcraw do use them.
>Peter, I believe you're right that there is a masked area >around the perimeter used as a black reference. I also >believed there is a perimeter of pixels that are used for >interpolation data in the demosaic process that is also not >used in the image. But I believe other converters such as >dcraw do use them.
Hi. Do you mean some extra pixels around the periphery for the demosaicing algorithm to have a full set for its calculation? I suppose that makes sense.... Peter