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07/17/2007 04:04:42 PM · #1 |
| I recently purchased a Samsung NV7Ops rated at 7.2 megapixels. When I right click on a photo and click 'properties' the size is listed at around 3.3 MB. I am confused about megapixels and megabytes. I thought a 7.2 megapixel camera would yield around 6 or so MB. My Nikon D70s is rated at 6 megapixels, and yields 5.8 in size. What am I missing? I mean besides brains! |
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07/17/2007 04:06:06 PM · #2 |
The file size of a JPG image will vary greatly based on the content of the image. Color and texture variations increase the size of the file. A jpg image of solid white, black, or any other single color will be very small.
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07/17/2007 04:07:21 PM · #3 |
Could be the file type you are saving them.
Generally if you save as a Jpeg instead of raw...jpegs will of course have a lower MB.
You would also have to look at the quality. Is it normal, fine, or super fine. Super fine would have a higher MB. I'm sure if you just bought the camera and didn't play around with the settings, it's sitting at normal or fine and/or jpeg. Which is why it's at 3.3MB |
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07/17/2007 04:13:25 PM · #4 |
The pixels on a dslr are a lot bigger than the ones on a normal point and shoot, they therefore capture much more information giving you the better picture quality. The jpegs from dslrs are also not always processed as much as those from a point and shoot, giving it larger file sizes as well.
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07/17/2007 04:15:54 PM · #5 |
Originally posted by SamDoe1:
The pixels on a dslr are a lot bigger than the ones on a normal point and shoot, they therefore capture much more information giving you the better picture quality. The jpegs from dslrs are also not always processed as much as those from a point and shoot, giving it larger file sizes as well. |
well a jpg getting compressed in a dslr goes through the same steps as getting compressed in a P&S. wb,sharpening, saturation all happen in both when you shoot jpg |
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07/17/2007 04:21:45 PM · #6 |
Originally posted by jmsetzler:
The file size of a JPG image will vary greatly based on the content of the image. Color and texture variations increase the size of the file. A jpg image of solid white, black, or any other single color will be very small. |
I have it set at 7 mp and Super Fine. Does this mean the largest file I'm going to get from this camera is half of what it is rated for? |
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07/17/2007 04:24:28 PM · #7 |
Originally posted by cogerox:
Originally posted by jmsetzler:
The file size of a JPG image will vary greatly based on the content of the image. Color and texture variations increase the size of the file. A jpg image of solid white, black, or any other single color will be very small. |
I have it set at 7 mp and Super Fine. Does this mean the largest file I'm going to get from this camera is half of what it is rated for? |
no no no. a 7mp photo will always have 7 million pixels. But its what those pixels are recording that makes the mb. shooting a detailed photo with lots of colour and tones it will be a bigger file in mb, but it will still only have the 7million pixels, but ifyou take a photo with lots of one colour or black and white it will be alot smaller file in mb, but still have all 7 million pixels |
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07/17/2007 04:24:47 PM · #8 |
Originally posted by noisemaker:
well a jpg getting compressed in a dslr goes through the same steps as getting compressed in a P&S. wb,sharpening, saturation all happen in both when you shoot jpg |
Right but is the process the same? A P&S is trying to just take photos, not as much emphasis is placed on quality. An SLR goes for quality, so the compression may not be as intense as it would be in a P&S.
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07/17/2007 04:31:05 PM · #9 |
Originally posted by SamDoe1:
Originally posted by noisemaker:
well a jpg getting compressed in a dslr goes through the same steps as getting compressed in a P&S. wb,sharpening, saturation all happen in both when you shoot jpg |
Right but is the process the same? A P&S is trying to just take photos, not as much emphasis is placed on quality. An SLR goes for quality, so the compression may not be as intense as it would be in a P&S. |
that would rely in the resolution you choose, "fine" say on a Canon SD850 will be the same as "fine" on a 30D. The main difference in quality you get is the much bigger sensors in the dslrs and the pixel density |
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07/17/2007 04:34:14 PM · #10 |
Here is a photo I took Sunday at the GTG. Before being resized it was 2.98 MB in size. Does that make sense in a camera rated at 7.2 MP?
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07/17/2007 04:35:48 PM · #11 |
All you can do is set your camera for the best-quality/lowest-compression JPEG of which it's capable. From that point, the actual compressed size will depend on the subject matter; more detail/more colors = bigger file:
Sunlight through maple leaves = 5MB
Foggy beach at dusk = 2MB
The uncompressed size will always be the same as long as you don't crop/resample or change the color mode ...
Message edited by author 2007-07-17 16:36:32. |
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07/17/2007 04:37:18 PM · #12 |
Extremely loaded question. It encompasses image file formats, color spaces and their storage format (bits per pixel), bits and bytes, megabytes/kilobytes as powers of 2, megapixels versus actual image size, and most importantly compression.
Compression is the key in JPEGs.
But let's start with the pixels.
First, in typical images, there are 8-bits for red, green, and blue, totaling 24-bits per pixel. (Grayscale may only have 8-bits per pixel, high quality images may have more bits per pixel, some formats support an alpha (aka transparency) channel with 8 more bits per pixel, some formats support animation, etc.)
But typically, there are 24-bits per pixel. 8-bits equals one byte. So, 3 bytes per pixel uncompressed.
On to the uncompressed image
Your 7.2 megapixel camera likely renders images with somewhere around 6.9 million pixels - sensor size is reported as a marketing gimic - some are wasted. So, 6,900,000 pixels at 3 bytes per pixel is 20,700,000 bytes, or 19.74 megabytes (1 megabyte = 1024*1024 bytes).
In uncompressed TIFF or bitmap format, your file will be slightly larger due to image header information (image width, height, format version, color information like 24-bits per pixel, meta data, etc).
Your actual image size is the width x height of your resultant image. This can be adjusted in camera usually as a small, medium, and large setting. Multiply this by 3 bytes, and that's your uncompressed, 24-bit per pixel image size.
Okay, let's compress it
Now take your 6.9 million pixel image and compress it as a JPEG.
How big will it be? It depends, and it's impossible to predict.
It depends mostly on the compression level (opposite of quality). At high quality, the image will be large-ish (though likely not as large as the uncompressed image), and at very low quality, it will be very small.
But John alluded to something more subtle. The actual image will vary the size of the JPEG because more complex shapes in the images (high contrast, lines, etc) will require more data to be properly represented.
The quality setting is often referred to as fine or super-fine in your camera. Don't mistake this with changing the resolution (large, medium, small) - see image size above.
JPEG is also a lossy compression method. Lossless compression methods (like TIFF compression using zip or LZW, or PNG) generally result in larger image files, but suffer no image degradation. The final file size in lossless compression is also simply unpredictable, but probably less than the original, uncompressed, 3-bytes per pixel.
What about RAW?
But Jeff, you say. RAW images are smaller than 3 bytes per pixel! My 7.2 megapixel camera generates RAW images around 9.9 MB. What's going on?
True, and I just learned this recently - RAW images store 12-bits per pixel. This is 1.5 bytes per pixel. This is because RAW images actually don't store red, green, and blue values per pixel. Each pixel sensor in your camera is colorblind, and has a physical red, green, or blue filter. The color information is distributed to the surrounding pixels later, and this process is known as Bayer interpolation. (See here for much more info on RAW).
Also note the difference between megabytes (MB), 1048576 bytes, and megabits Mb (10148576 bits, or 131072 bytes), and kilobytes (kB), 1024 bytes.
So there you go. Much more information than anybody ever wanted about image filesize. I'm going to simply refer to this post if anybody ever asks this again. =D
Cheers,
-Jeff
Message edited by author 2007-07-17 16:46:55. |
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07/17/2007 04:38:16 PM · #13 |
1 megapixel does not one megabyte equal.
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07/17/2007 04:42:38 PM · #14 |
You can do a test to see how color information effects the file size by covering the lens of the camera.
1. take a picture of something colorful like a landscape shot.
2. then take a picture with the lens cap on or if no lens cap cover the lens so it takes a black picture.
3. now compare the megabytes between the two pictures. |
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07/17/2007 04:50:42 PM · #15 |
| Ok, so here's the bottom line. I bought this camera because I wanted an ultra compact to carry around when hiking, biking, walking, etc., but I also wanted to get good results. After researching the cameras that were available on the market this one had the best combo of mp, zoom, and flexibilty (can be fully manual). Now I'm wondering if I could do better. Should I consider returning it (still within the 14 day return period) and do more research? Or, is this as good as it gets in the compact camera genre for the price range of +- $300. |
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07/17/2007 04:52:56 PM · #16 |
Ok, since no one has explained this easily yet. Let me try.
Your 7 megapixels is reffering to the physical size of the image, which in your case is 3072 pixels x 2304 pixels = 7077888 pixels total in the image, which is basically 7 megapixels.
The "image size" that your jpg is when you copy it from your camera onto your drive has very little to do with the total number of pixels. It has to do with the storage space it takes your computer to store that 7 megapixel photo. So if it is compressed like a jpg it will likely be much less than 7MB, however a MB is not like a megapixel anyways. that is like apples and oranges.
Think of the megapixels as being the physical size of a an area, (length times width) which refers to it's physical size. Then imagine the megabytes as being the weight of that area, which will differ greatly depending on if it is a slab of concrete or a peice of paper, both the same physical size..but much different in weight. The megapixel referring to, and measuring a totally different thing then the megabyte.
Does that make any sense? |
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07/17/2007 04:53:14 PM · #17 |
Originally posted by SamDoe1:
The pixels on a dslr are a lot bigger than the ones on a normal point and shoot, they therefore capture much more information giving you the better picture quality. The jpegs from dslrs are also not always processed as much as those from a point and shoot, giving it larger file sizes as well. |
His Point and Shoot files are larger then his dSLR's so your statements dont even match up. But your right on some points.
Sharpening causes larger JPEG files, There is a signifigant decrease in file size by using my Powershot A630's default sharpness. If i turn it up though i go from say 3 megs like you to 5 megs.
It is odd for the dSLR to put out a larger file only thing i can think off because SamDoe is right that they are not as procesed but they might be saving as JPEG100 100% quality. But even so Sharpening has a much more signifigant affect
Pixel Quality is one thing, pixel physcial size in the end doesnt affect filesize. Since were talking jpeg versus jpeg the 8 bit pixel is the same definition length as another 8 bit pixel, however in raw from a dslr the 16 bit pixels (12 bit in reality) are twice as large.
Point 1 - Less processing of an image (sharpening and what not) will actually result in a smaller file.
Point 2 - 8 bit pixels are 8 bit pixels, in file size they dont make a difference. The only "bigger pixel" is from a raw file where the pixel is always the same size but the file size is larger due tot he color being defined by 16 bits (12 bit source) rather then 8. |
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07/17/2007 04:55:34 PM · #18 |
Filesize is not an indicator of quality, and only a vague indicator of resolution. My Rebel XT often produces images in the 3-4 megabyte range, if it makes you feel better.
I can't speak to the quality of that particular camera. |
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07/17/2007 05:10:21 PM · #19 |
Originally posted by basssman7:
Ok, since no one has explained this easily yet... |
I prefer accuracy to ease of understanding. Sorry if my post missed anybody, but it's correct.
Or, you can imagine something simpler if it suits you, I don't care. |
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07/17/2007 05:17:43 PM · #20 |
Originally posted by cogerox:
I recently purchased a Samsung NV7Ops rated at 7.2 megapixels. When I right click on a photo and click 'properties' the size is listed at around 3.3 MB. I am confused about megapixels and megabytes. I thought a 7.2 megapixel camera would yield around 6 or so MB. My Nikon D70s is rated at 6 megapixels, and yields 5.8 in size. What am I missing? I mean besides brains! |
Megapixels = ( width in pixels X height in pixels ) / 1,000,000.
That's it. |
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07/17/2007 06:10:48 PM · #21 |
This has possibly been mentioned (I didnt read it all)
A photo of a white wall will differ in size from a photo of a black wall. SCIENCE! |
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07/17/2007 11:14:35 PM · #22 |
| Heres a good example. I took photos at a rock concert and each file averaged between 3-4mb. did an outdoor photoshoot(for a challenge coming up fairly shortly) and average for those was 7mb+ |
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07/17/2007 11:22:09 PM · #23 |
Originally posted by ajdelaware:
This has possibly been mentioned (I didnt read it all)
A photo of a white wall will differ in size from a photo of a black wall. SCIENCE! |
And both will be smaller than a photograph of a checkerboard...
R.
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07/17/2007 11:28:12 PM · #24 |
its better if u blow highlights on the white of the checkerboard the less detail you have the less space (due to less defined colors, decreasing contrast or saturation might help?)
Message edited by author 2007-07-17 23:28:21. |
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07/17/2007 11:29:51 PM · #25 |
Originally posted by jmsetzler:
1 megapixel does not one megabyte equal. |
this is the simplest answer to the original question :)
and i'd like to add an example, the 6MP Fuji S5Pro can create a 25MB RAW. |
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