Digital Camera Question

[Lawreston]

My camera is rated to handle 24.6MP. I was doing a shoot on a gorgeous Easter and when I downloaded the 50+ images they were averaging anywhere from 18 MP to 23.7 MP. I was shocked, when doing some post processing, to see several files at 25.9 MP. How can that be? Even after "tweaking" some images the reworked files were 19.2 to 23.4.

Understand that I'm a User; don't generally care about what technical details
make the system work. But the 25.9 beguiles me.

HR

 

[Areeda]

HR,

Are you confusing MP with MB?

MP - mega pixels should be constant for a selected resolution 24.6 MP would be something like 23Kx18.5K

MB - mega bytes would be the amount of storage required to save the image. If there were no compression it would be MP * 3 (for red,green,blue). Storage formats like JPEG will have different compression ratios depending on content. For the worst case a completely random image cannot be compressed a single solid color only takes about 100 bytes.

Joe
edit: a completely random image cannot be compressed WITHOUT ERRORS

 

[wbarnhill]

MP is megapixels. They don't directly correlate to Megabits or Megabytes.

Let's say each pixel can contain 8bits of information regarding each of the three colors in the primary spectrum ( RGB ), so together that's 24 bits, or 3 bytes of data per pixel. With a 24.6 MP camera, pulling RAW files you could theoretically get a 73.8 MB file. Most will fall well short of that, and when you throw a compression technique like JPEG into the mix, you get even smaller filesizes.

 

[Cap'n Jack]

HR,

<SNIP>
Joe
edit: a completely random image cannot be compressed WITHOUT ERRORS

For the JPEG compression probably being used, you are essentially correct, although I would have phrased it somewhat differently.

As there are lossless compression schemes (LZW, run-length encoding, and others) used for images, the statement isn't strictly true. It is possible for a completely "random" image to require greater space upon lossless compression than the original image, but these "images" tend to only occur in a computer science lab.

 

[Areeda]

For the JPEG compression probably being used, you are essentially correct, although I would have phrased it somewhat differently.

As there are lossless compression schemes (LZW, run-length encoding, and others) used for images, the statement isn't strictly true. It is possible for a completely "random" image to require greater space upon lossless compression than the original image, but these "images" tend to only occur in a computer science lab.

There is a lossless-JPEG also, and I THINK some of the high end cameras use it.

I agree truly random images are rare. I saw plenty of them in Nuclear Medicine though.

Harley gets the idea (plenty of geeks of all technical persuasions on this board).

Joe

 

[Lawreston]

Thanks for the responses. I had to go back and re-read what I'd written.
Corrected data: The camera is 24.6 Mega pixels, 35mm Full Frame.
And those files: are 25.9 Mega bytes; original files are normally 6048 x 4032.

The 25.9 MB files are the largest I'd seen and blew my mind(doesn't take much). I've had 16" x 24" prints done from many images; and my lab said the files would support enlargements to 40" x 60"(which I've yet to order). (( but I might))

HR

 

[mantakos]

JPG is 24 bits per pixel (three 8-bit color channels), so 24MP would make for a 72MB file if there was no compression. Anything less than 72MB is the result of such compression, with the amount of savings dependent on the contents of the image.

A raw file from that sensor is 12 bits per pixel, so a 24MP raw file would make for a 36MB or 48MB file without any compression, depending on how they pack the bits into bytes. Some cameras do apply lossless compression to RAW files.
-harry

 

[Lawreston]

I haven't played with raw files yet because my photo lab in Texas requires JPG files. And this particular camera, added to my other 10.2 MP body, will do a lot more than to what degree of performance I'm subjecting it. Additionally, the speed at which those near 26 MB files are being handled by my PC is probably suggesting that I'd be wise to install some added RAM. It's always something!

HR

 

[wsuffa]

That's not too big at all.

The CR2 raw files from my Canon 7D range up to 29 megabytes.

I'm in the process of scanning some old slides & negatives at 5400 pixels/inch - the TIFF files that are created run from 50 megabytes up to 200 megabytes. The associated jpegs are about 5-7 megabytes each. I've scanned 1600 pictures and counting....