7.2Meg Camara gives 2 Meg files?

I just bought a Panasonic DMC-TZ3 at Costco and love the 10X optical zoom. One thing that I haven’t figured out yet is why it is advertised as a 7.2 Meg camara when the files on my computer show up as somewhere around 2.1 meg. I have the setting set a max of 3072 x 2304 pixels. Shouldn’t my files be huge? Why not? :confused: The files are no bigger than what I got with my 3-1/2 year old Pentax Optio-S 3.2meg camara, so I’m feeling like I’m being purposly confused by marketing people and I don’t like that feeling. What am I missing o teeming millions?

3072 x 2304 pixels of 16-bit raw data would be around 14MB (megabytes) as a RAW file. Most cameras will shoot JPEG by default, a lossy compression method, and while size varies with compression ratio set by the camera and YUV color space used (444,422,420,etc.) I’d say a size of about 2MB is fairly reasonable for a 7MP image.

Or are you saying the pictures only have 2 megapixels in them? If so, you probably accidentally set your camera to shoot 2MP pictures, check the menu. 2 megapixel RAW images would be about 4MB for 16-bit, and JPEGs probably 500-800KB.

P.S. Your Optio might have used a different compression ratio/color space. On most Panasonics I have seen there is a quality setting right there in the menu that’s something like 1 bar, 2 bars, 3 bars and then “TIFF” and “RAW” (if your camera supports them). The JPEG quality setting is the quantization/compression ratio and will affect file size significantly (that’s what it’s there for, otherwise there would be no point in ever shooting lower quality shots).

Because your camera saves your pictures in JPG format, which compresses the data. If your camera saved the data in an uncompressed form, your pictures could be upwards of 200MB each, so you could only fit a few on a single flash storage card. The pictures from a 7.1MP camera should be larger than a 3.2MP camera though, I have no explanation for that, unless the larger camera is using a higher compression ration.

That seems like a possibility to me, the various Canons in my office give you options which I think change the amount of compression (this is what I assume is happening when I change from “Standard” to “Fine” to “Superfine”).

My crummy little PowerShot A550 7.1 megapixel camera just gave me about a 3.5 megabyte file using the same resolution setting the OP is, at “superfine” detail. JPEG compression, naturally, though I think I can change it to TIFF if I want (I’ve never needed to try).

If a 7 megapixel camera is producing 200MB uncompressed images something is wrong. The majority of cameras will use a Bayer-like color filter mosaic for 8, 12 or 16 bit per filter read-out. At 7 megapixels that gives between 7 and 14 MB. If your camera does color interpolation before saving “RAW” data, then even the biggest color space of YUV444 at 16-bits per pixel would give you 42MB.

The small minority of cameras that use RGB CCD sensors (like Sigma) would require 24 million photosensors for a true 7MP image. Marketing would jump on that and call it a 24MP camera, so a 7MP RGB CCD would only capture effective 2.3MP images, yielding the same RAW sizes.

To summarize:

3072px x 2304px = 7,077,888 pixels = 7.1 megapixels.

Megapixels ≠ megabytes.

7.1 megapixel images will result in differering file sizes depending on how good the camera’s compression algorithms are as well as what compression settings have been specified by the user.

In short, you were not ripped off.

Part of my confusion is why wouldn’t “pixels = bytes”? Don’t they both describe one data point being either on or off, high or low, 1 or 0?

On or off would only allow two colors, black or white. In order to render color, each pixel has a color depth, typically ranging from 8 bits to 24 bits.

Not really although you are getting into compression schemes. You usually don’t need describe every single pixel even if the compression is lossless and sacrafices no information.

Imagine that I take a picture of the sky and then imagine how we might describe a small set of pixels:

BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky+BlueSky

I could also just say 20xBlueSky and store that in much less space and say the same thing.

COmpression algorithms can get complicated and there are many types that sacrafice some information but make a much smaller file like JPEG. However, the important point is that there doesn’t need to be a dedicated byte to every pixel.

Aha! :smack: Thanks :cool:

Nope. For one thing, the off/on thing is a “bit”, not a “byte”. A byte is 8 bits which is enough to represent one ASCII character (e.g. ‘a’). A color pixel in your digital camera is probably 24 bits, with one byte each for red, green, and blue intensities.

I’m no software engineer, but I think you’ve got something wrong. A “bit” is binary (yes/no, on/off, 1/0, etc.). A byte is 8 bits.

Secondly, a “pixel” is a picture cell (pic-cel ->pickcel ->pixel). A pixel requires many bits and bytes to describe it (position, color, brightness, etc.)

Therefore, a pixel does not equal a byte.

News to me. I had always heard that pixel is short for “picture element”.

No. A byte is 8 bits, so it describes 8 data points being on or off. A pixel is any computer representation of a (usually rectangular) sub-block of an image that is of one color. The more bits you devote to each pixel the more color fidelity you get. A pixel is not either “on or off”, most of the time. A pixel generally represents a color value that is more than 1-bit. The way this color value is encoded is called a color space. Most cameras I’ve seen use the YUV420 or the YUV422 color spaces after interpolation.

Now, a pixel would be a byte if you were using an 8-bit per pixel representation. This only gives you 8-bits of color information per pixel, and would mean your color depth would be only 256 colors (i.e. a maximum of 256 different colors in the image).

This is exactly the reason I post my questions here instead of searching through and trying to understand Google searches and wikipedia articals. Even a caveman can understand the explanations here. :smiley: Thanks. :cool:

Oh no! This changes everything!

Okay, I don’t have a cite. I just picked that up somewhere and accepted it as fact. It does make sense, though, doesn’t it?

Look, I’ve been dealing with middle schoolers in their last days of school. You’d be out of your mind, too.

Nah, just the little bitty things.

Well, I appreciated the correction, at any rate.

Something interesting you can do to see something similar to this compression in action is to make two text files. Fill one with a bunch of A’s and another one with a story (bunches of letters in random order). Make them the same exact size and then use Winzip or WinRAR to compress them. It will be able to compress the one with all As a lot more than the one with the story. My example

Text file with all As compresses 126,976 bytes down to 167 bytes.
Text file with story compresses 126,976 bytes down to 2,458 bytes.