scaling down a 8mp picture creates better quality?

Question

my dad thinks i can take a 8mp camera, and zoom the picture down/size it down and it will have a better picture quality, because it "smashes down" the 8mp into a smaller area. is this true or possible?

Answer 1

That's not quite the way it works.

When you downrez a picture, you create a new file with less pixels than the original. Like you say, the original pixels are averaged out. This creates a smaller file (which is nice for email attachments) but the net effect is that you have less pixels than you began with. In other words, you threw information away. Throwing information away only reduces quality.

Here's the trick though: your prints do sometimes APPEAR better by reducing the size. And the reason for this is simple: when the entire image becomes smaller, so do any flaws.

True image quality is mostly determined by the lens and to a smaller extent by the quality of the sensor and the in-camera software. Mostly by the lens. This is why professional photographers spend thousands of dollars their lens collection.

Megapixels only determine the maximum size of the print. With more megapixels, you can make larger prints. With 8 megapixels, you can make superb prints as large as 8 x 12 inches. With 4 megapixels, you'll notice degradation with prints larger than 4 x 6 inches.

The best thing to do, is to take pictures at the highest resolution and to use those for your prints. If you know how to retouch pictures with Photoshop or something, go ahead, but leave the resolution as high as possible. (You paid for an 8MP sensor, so you might as well use it.)
The only reason to reduce the resolution is if you actually need small files. I reduce pictures to 800 x 600 pixels for email attachments, my web page, and other internet purposes. This way, a 3MB file shrinks to around 100 Kb.
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Sam,
Impressive stuff, but I think you're making this more complex than neccessary. Please correct me if I'm wrong...
In a perfect world, you'd print everything at 300dpi. You can get away with less, but why would you want to? 300dpi is about the maximum that the naked eye can resolve up close. Going higher than 300dpi is overkill, because you can't tell the difference, and going lower than 300dpi means that you lose more and more detail.
A 4MP file is sufficient for a 6x4 inch print at 300 dpi. One pixel on the sensor will roughly correspond to one dot in the print. An 8MP file will be massively downrezed by a print shop to fit 4x6 at 300 dpi. At 4x6 inches, the two prints should look identical, because both files contain more than enough pixels.
At 5x7 inches, the 4MP picture doesn't have enough pixels anymore - it needs to be slightly interpolated to print at 300dpi. The 8MP file will still be downrezed. You should start to see a tiny bit more detail in the 8MP print. This difference will become more apparent the larger you print.
Even at 8x12 inches, the 8MP file will still look great. At this size, the 4MP file will not. What's more, it doesn't matter if the 4MP file came from 4MP camera, or if it started life as an 8MP file that was downrezed to 4MP. Once you have a 4MP file, you simply don't have enough resolution for large prints.
The sharpness on your computer monitor is another matter. The naked eye can percieve up to 300 dots per inch, or pixels per inch, but your monitor can only display 72ppi. On a computer monitor, trying to display anything more than 72ppi is futile.

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Sam, my apologies. Reading back my own addition, I don't know what the hell *I* was thinking.

Answer 2

The easiest way to find out what happens is to take a picture.
Open the picture in Photoshop or Photoshop Elements.
Click on "Image" then "Resize" then "Image Size"
(Or use [CTRL]+[ALT]+[I] < Look at "Resolution" on the window that opens and it will show you what the resolution of the image is.

I've been doing this for 10-15 minutes to see what the difference is. I tried with a Nikon image, which starts life as 300 ppi and then a Canon image, which starts life as 180 ppi.

The more I play with it, the more baffled I get. I see what your dad is talking about, but I'm not sure that it translates into a real world benefit. It doesn't for my eyes, anyhow.

The numbers are more dramatic with the Canon, so I will discuss that example.

An original 10 MP image is 3648x2736 pixels. This would print at approx. 20"x15" at 180 pixels per inch, if only I had a printer that big.

I cropped it to 7"x5". This produced an on-screen image of 3648x2606 pixels, but the resolution increased to a whopping 521.143 pixels per inch. It turns out that each image, which was as close to an identical crop as I could manage was approx 500 pixels by 500 pixels.

I then swapped back and forth time after time (using [CTRL+Z] followed by [CTRL+Y] several times) and examined the screen under magnification. The display, viewed at full size, did not seem to change at all. My screen resolution is set at 1024x768 pixels, which is (voila) the "classic" 72 pixels per inch. If I "increase" the resolution of my monitor, things get so small it is irritating to read them.

My first conclusion is that there is no difference on the monitor between 180 ppi or 521 ppi, if I am only displaying 72 ppi anyway.

I then did a test print of this image, using the best resolution available. I "free cropped" the same portion of each image with "no restriction," which means I did not alter the ppi by cropping. The final result of the test area was still 180 ppi in one and 521 ppi in the other. I printed each. The 180 ppi sample printed at about 2.5"x2.5". The 521 ppi sample printed at about 1"x1". Guess what. I just can't make a valid comparison between the images because one is so much bigger than the other! I'm magnifying and checking, and I can't say that I see a quality difference. I'll have to come back and do a much larger print and see what I think, but - YOU CAN DO THIS TOO and let me know what you think. I've got to get ready for work! My temporary conclusion is that it's true - we can't really see much difference in image quality once you get to the 180-200 ppi range and better. I've got a few Pentax images (72 ppi) that I will have to amuse myself with this evening.

Afterthought - this might be like looking at a 12" TV and then looking at a 32" TV. The 12" will appear to have a much more crisp picture, but you have to be 2 feet away to see the thing. I can't make sense of this right now, 'cause I have to hurry............. :-)

~~~ADDITION for OMG~~~

I know that I'm overthinking this and not drawing any conclusions. My real bottom line is that "downsizing" is NOT the same as "downrezing." Cropping the whole 300 ppi image from 10"x6.6" to 7"x5" "raises" the resolution from 300 ppi to 400 ppi. You can not see this on the monitor or on the print, though, so it's a theoretic gain and not a practical (or real?) gain. As I have said many times, I prefer to work on HUGE images (such as the 4800 ppi I use when scanning slides) and then downrez them to 300 ppi when I am really done and ready to print or archive the image. You might remember a long piece I wrote and posted a few times about all the different resolutions available (but fixed) from the various manufacturers and how - in the end - they all produced virtually identical prints or screen images.

The question in my mind is what Zero actually means by the term "scaling down." I took it to mean going from 10"x6.6" (for instance) to 7"x5" by cropping most of the original image to a smaller size.

~~~MORE FOR OMG~~~

That's the punchline to a joke.

"Psychic? ME?? Heck no, I'm not psychic. Most of the time I don't even know what the heck _I'M_ thinking!"

Answer 3

The hunt for megapixels Cramming 12 megapixels into the TINY sensor on one of those compact P&S cameras is a very bad idea. The more pixels you force together, the more problems (such as digital noise) it creates. Some people seem to think megapixels is the be all and end all of camera quality, but that is very wrong. Any more than 5 or 6 in such a tiny sensor only causes grief. If you want better quality, you need to get a bigger camera with a bigger sensor. Keep in mind that there are many other factors apart from pixel count that affect the quality of the image.

Answer 4

Your dad is correct in principle, but wrong in normal practice.

If you take your 8 mp image and print it billboard size, it will be fuzzy or worse. If you reduce it to 6x4.5 inches, it will be much, much clearer.

However, on average our eyes can only see a difference down to about 300 pixels per inch (ppi). So most printers do not print any smaller than that, and if they did, no one could see the difference anyway!

Some older printers used to get mixed up when given too much ppi and try to put too many inkdrops into too small a pixel. The result was a smear.

Today, printer driver software often is programmed to throw out pixels if you give it more than it can handle for the print size you want.

So the best strategy is to take and save your pics at the highest resolution and quality. Do not Resample and throw away pixels.

Let the photo editing (or printer driver) software "Scale" your pixels into the physical sized print you want. You will get great results until you get up to some maximum size where things start to blur.

Good Luck

Answer 5

what?????????? okay NO>>>

if you have a digital camera 8 MP
and you use the zoom. what it will do it will scale the quality of the picture down; meaning zooming a whole lot on a picture will make it look grainy and dark... it will not do anything better for you....

do you know why 7 is afraid of 9? cause 7 - 8 - 9 jaja
so scaling to 3 mp will not be better than 8 mp!

but, if you take a 8 mp photo and strech it to a bill board size picture it will ruin it cause there is not enough quality for that kind of strech.. but if you take a 8 mp photo and print it to a 4x6 paper it will lokk awesome on the paper....

Answer 6

Your father doesn't know what he's talking about. There's no such thing as "smashing down" a picture. If you decrease the size of the picture, you also decrease the detail.