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Megapixel myth
Hi All. I believe I am a victim of the megapixel myth and needed to get some opinions from people with more experience than myself. Let's say I have a 6 megapixel camera with 1/2.5' sensor. For best image quality, should I use the camera in 6 mpix mode or I should decrease that one? If I use lower mpix, is the camera going to capture the same image width and hight (but with less "dots") or it will capture "smaller" image (not as wide)? Thank you all in advance!..

Comments (11)

When the imaging sensor is created, the pixels/photon detectors are created, for better or worse. "They are what they are"..

Adjusting the "image size" captured via a menu selection does not alter the size/quality of the pixels/photon detectors. Sorry...

Comment #1

It sounds like you are talking about the tradeoff between resoluton and noise. Packing too many small pixels onto a sensor results in an apparently high resolution but at the cost of high image noise (a high inherent uncertainty in the readout from each pixel)..

In your 6MP camera you could take a 3MP picture in one of two ways. Either the camera will only use half of the pixels, in which case there will be no improvement in image quality. or you could use all pixels and average the output from an adjacent pair to give one larger pixel. This is called 'binning':.

Http://www.noao.edu/outreach/aop/glossary/binning.html.

Either way, you might as well take the 6MP image and downsize it in post-processing. The image quality (however you define it) achieveable with a camera depends on the the amount of light captured by the sensor. No post-processing tricks can create information that isn't there. The only solution to get better IQ is to use a camera wiwth a bigger sensor..

Best wishesMike..

Comment #2

Mike703 wrote:.

Either way, you might as well take the 6MP image and downsize it inpost-processing. The image quality (however you define it)achieveable with a camera depends on the the amount of light capturedby the sensor. No post-processing tricks can create information thatisn't there. The only solution to get better IQ is to use a camerawiwth a bigger sensor..

Best wishesMike.

If The camera takes a 3 mp usign pixel binning (and not taking only the center 3 mp of the sensor), then it could be advantageous to take the photos directly in 3 mp beacause one could pack more photos on their memory card..

But you have to be sure that your camera does this. If in doubt or if you have enough memory card, then I agree with Mike that downsizing in post-processing would probably give the best results.Claude Carrier..

Comment #3

Edinuser wrote:.

Hi All. I believe I am a victim of the megapixel myth and needed toget some opinions from people with more experience than myself. Let'ssay I have a 6 megapixel camera with 1/2.5' sensor. For best imagequality, should I use the camera in 6 mpix mode or I should decreasethat one? If I use lower mpix, is the camera going to capture thesame image width and hight (but with less "dots") or it will capture"smaller" image (not as wide)?.

To a computer an image is only measured in dots. An image with more dots will be bigger than one with fewer dots - there are no 'bigger dots' or 'smaller dots' - there are only 'dots'. Both images can be 8x10, but one will have - for example - 150 dots per inch, wheras the other may only have 72 dots per inch. Inches only comes into play when you print...

Comment #4

IMac, therefore iAm wrote:.

Edinuser wrote:.

Hi All. I believe I am a victim of the megapixel myth and needed toget some opinions from people with more experience than myself. Let'ssay I have a 6 megapixel camera with 1/2.5' sensor. For best imagequality, should I use the camera in 6 mpix mode or I should decreasethat one? If I use lower mpix, is the camera going to capture thesame image width and hight (but with less "dots") or it will capture"smaller" image (not as wide)?.

To a computer an image is only measured in dots. An image with moredots will be bigger than one with fewer dots - there are no 'biggerdots' or 'smaller dots' - there are only 'dots'. Both images can be8x10, but one will have - for example - 150 dots per inch, wheras theother may only have 72 dots per inch. Inches only comes into playwhen you print..

There are bigger/smaller "dots" on the image capture side. A 12MP 1/2.5" sensor has a lot smaller "dots" than a 12MP full frame sensor. Those smaller dots get less light hitting them..

Anyway OP- use the native resolution. The lens is probably the weak link anyway.-..

Comment #5

Thank you all for the information! I believe it is more clear now:)..

Comment #6

If it has 6 million sensors then the 'natural' output size is 6Mp..

Using a smaller size means you rely on the camera's own firmware to scale that down. This may not produce the best result, as your desktop software can use more sophisticated algorithms to give a better result..

As you can easily batch resize image the only reason to use a smaller size is to save space. I'd describe it as an 'emergency only' thing. If you regularly find yourself running short of space get a new card - a spare and keep it with the camera..

StephenG.

Pentax K100DFuji S5200Fuji E900PCLinuxOS..

Comment #7

Sjgcit wrote:.

If it has 6 million sensors then the 'natural' output size is 6Mp..

No Stephen, that isn't right. The relationship between Megapixels in the sensor, and Megabytes in the file, is rather more complicated than a simple 1 to 1. It depends a good deal on the type of file being saved..

Taking the 6MP as an example .....

1) As an uncompressed 8-bit TIFF, a 6 Megapixel image would likely consume about 8.9 Megabytes of drive space... (a camera RAW would take just over 1/3rd of that.).

2) When compressed into a good quality JPEG, this would shrink to 1.3 to 1.6 Megabytes. The exact figure varies from shot to shot, depending very much on.....

I) just how much compression is selected at the point of saving...

Ii) and on just how efficiently the image CAN be compressed (depends on how much fine detail is in it)....

Note: BOTH these files would open at the full 8.9 Megabytes when undergoing editing in software like Photoshop.Regards,Baz..

Comment #8

I have been thinking is there a perfect ration of sensor size to pixel? like some perfect rectangle or golden ration and stuff..

Comment #9

I'm so sorry, folks...

In my previous post I read from the wrong column in my calculations. As a result, my figures are quite WRONG ... which fact I very much regret.(Hmmm.... That'll teach me to pontificate all over the place!) .

Please see corrections below.......

Barrie Davis wrote:.

Sjgcit wrote:.

If it has 6 million sensors then the 'natural' output size is 6Mp..

No Stephen, that isn't right. The relationship between Megapixels inthe sensor, and Megabytes in the file, is rather more complicatedthan a simple 1 to 1. It depends a good deal on the type of filebeing saved..

(So far, so good!).

Indeed, the relationship in a full sized file is NOT one byte per pixel, it is more like THREE bytes per pixel (for 8-bit UN-compressed TIFF files).... that's one byte for each of three colour channels per pixel (Red,Green and Blue, respectively)..

Taking the 6MP as an example .....

1) As an uncompressed 8-bit TIFF, a 6 Megapixel image would likelyconsume about 8.9 Megabytes of drive space... (a camera RAW wouldtake just over 1/3rd of that.).

(This is where I started to go wrong..).

This SHOULD therefore read 3 x 6 = 18 Megabytes approximately..

Only approximately??.

Well, because megabytes are not DECIMAL (1 kilobyte equals 1028, NOT 1000)but megapixels invariably ARE decimal......

.... the relationship is approximately 2.85 megabytes to the megapixel, instead of a full 3..

In addition to this, there may be as much as another 300kb or so in each file, for headers and other meta-data etc.... (the precise figure varies from one camera marque to another) which pushes it back up again ... if not so high as three times the megapixel count..

A) The above information relates to full size UN-compressed 8-bit TIFFs as saved to disk, or as opened in memory when being edited in Photoshop, say..

B) Losslessly compressed Tiffs (LZW compression) are about half the size of UN-compressed..

(Note: It was compressed TIFFs to which I inadvertently referred in my earlier post. I apologise most sincerely for my mistake.).

Okay......

Most cameras these days do not save TIFFS directly because they are so bulky. They save as JPEGS or RAW..

RAW data come from the sensor with only ONE colour per pixel, and so start off about 1/3 the size of a TIFF..... but they are often in higher bit depths than 8 (10, 12, or 14) which pushes up their size. Then again, some manufacturer's RAWs are compressed before saving, which pushes them down again... (shrugs) so we cannot be entirely definitive about RAW file sizes in general..

So what about JPEG, which is another 3 channel per pixel type file??.

Well, with JPEG image files we can be even less certain about the relationship between megapixels on the sensor, and megabytes in the file. JPEG is a very efficient but LOSSY compressed format, and compression is variable under the direction of the user. So file size depends primarily on....

I) just how much compression is selected at the point of saving...

And also on.......

Ii) just how efficiently the image CAN be compressed....

....which itself depends on how much fine detail is in the picture. This is because JPEG efficiency of compression varies with how much image DETAIL is needing to be compressed.... for instance, pictures of trees with lots of fine texture make much larger JPEG files than pictures of cloudy skies..

File size rule of thumb for JPEG?.

Hmmm... Typically we should expect a HIGH quality JPEG to take up about 0.5 megabytes per megapixel... so 6MP (six megapixels) should close down to about 3 to 3.2 Mb of storage. Of necessity, as now may be clear, this figure is very approximate, and can vary greatly..

The important thing to remember is that when a JPEG is opened, and being worked on in Photoshop, say, it is the SAME size in memory as if it had been shot as a TIFF. Essentially it *becomes* a TIFF when it is open, because JPEG compression is just a method of *compact storage*.... NOT display!!Again....

Please forgive me for previously getting it so wrong. Shame on me, especially as I was prompted to post in order to correct someone else! I do hope I have made no further silly errors, and that my information is now, at least, 'closer' to correct..

Happy New Year, everybody. Regards,Baz..

Comment #10

Edinuser wrote:.

Hi All. I believe I am a victim of the megapixel myth and needed toget some opinions from people with more experience than myself. Let'ssay I have a 6 megapixel camera with 1/2.5' sensor. For best imagequality, should I use the camera in 6 mpix mode or I should decreasethat one? If I use lower mpix, is the camera going to capture thesame image width and hight (but with less "dots") or it will capture"smaller" image (not as wide)? Thank you all in advance!.

With Canon P&S cameras the entire sensor is always used for every image. Changing the resolution is a post-capture process..

The definition of "image quality" is a moving target. It is subjective and means different things to different people. For example, there is no question that more megapixels gives you more detail. If a persons primary interest is in the details of photographs of stamps, then more megapixels means more to that person than dynamic range. But to wedding photographers, dynamic range is so important that they use the Fuji S3/S5 cameras (which are unremarkable cameras except for their incredible dynamic range) despite the loss of resolution they suffer to get it..

So you have to first figure out what IQ means to you, then test your camera to see what settings most affect your image quality..

For small P&S cameras, changing resolution might reduce noise a tiny bit, but its the same effect you would get from resizing the image in software. Otherwise, youre always better off taking the full resolution image and manipulating afterwards if you want a different resolution...

Comment #11

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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