What is the minimum usable megapixel count ?

Wondering how you guys would respond to this:

http://finance.yahoo.c​om …ediacommentsugc​_container

"With seven megapixels, you can blow a photo up to the size of a poster with no issue."

Don't know what their idea of "poster size" is.

LV Moose wrote in post #16289182
Wondering how you guys would respond to this:

http://finance.yahoo.c​om …ediacommentsugc​_container

"With seven megapixels, you can blow a photo up to the size of a poster with no issue."

Don't know what their idea of "poster size" is.

If you view an 8"x12" 7Mpixel image from 12" away, then you can view an 80'x120' 7Mpixel image from 120' away and the perceived quality of the two will be IDENTICAL.

Wilt wrote in post #16289232
If you view an 8"x12" 7Mpixel image from 12" away, then you can view an 80'x120' 7Mpixel image from 120' away and the perceived quality of the two will be IDENTICAL.

Not with my poor eye sight they won't

Kolor-Pikker wrote in post #16289242
Not with my poor eye sight they won't

Pardon, I was assuming someone with 20/20 vision below the age of 40 when the arms become insufficiently long for reading!

Wilt wrote in post #16289232
If you view an 8"x12" 7Mpixel image from 12" away, then you can view an 80'x120' 7Mpixel image from 120' away and the perceived quality of the two will be IDENTICAL.

Okay, so 24"X36" poster viewed at 36" would be the same. Would 7Mpixels result in an image of adequate detail?

LV Moose wrote in post #16289272
Okay, so 24"X36" poster viewed at 36" would be the same. Would 7Mpixels result in an image of adequate detail?

Human eye is said to have resolution of 1.2 arcminute per line pair. At 36" distance that is .012528" for a line pair.

And it requires three pixels to represent a line pair, so you need three pixels within 0.012528" in order to represent a line pair that the eye could detect. Or a pixel every 0.006264", or 160 pixels per inch for 24"x36" print viewed at 36".

Assuming a camera with 2200x3300 pixels (7.26 Mpixel), we have 3300 pixels across 36", or 0.010909" between pixel centers on the print. Only 92 pixels per inch.

A 24x36" print viewed at 36" from 7Mpixel image does not equal the resolution of the human eye. Whether or not you have 'sufficient resolution' is a subjective judgement call. There are plenty of folks who have proclaimed satisfaction looking at a 24x36" poster made from only 8Mpixel image. Lots of folks have discovered that 'sharp' is more important than absolute detail.

Examples of satisfaction with a large print, in spite of being made from 8 Mpixel image...
https://photography-on-the.net …php?p=2400340&p​ostcount=3
https://photography-on-the.net …hp?p=2428578&po​stcount=16

LV Moose wrote in post #16289182
Wondering how you guys would respond to this:

http://finance.yahoo.c​om …ediacommentsugc​_container

"With seven megapixels, you can blow a photo up to the size of a poster with no issue."

Don't know what their idea of "poster size" is.

And I wonder what their idea of "no issue" is. Surely, a lot of the small details that we expect to see on a large poster will not be present if the original file is only 7MP.

And another thing - there seems to be this assumption that the larger something is blown up, the further the viewing distance will be. This is very often not the case. Many art galleries are in small buildings with small rooms. One cannot get 15 feet away from a painting in many galleries . . . unless you go outside, cross the street, and then look back thru a window. If a room is 20' by 15', and there are tall showcases and displays in the center of the room, you are pretty much standing about 4 feet from the wall nearest to you. You may be able to take a step back and view the stuff on the wall from 6 feet away. Try to take another step back, and you will walk into the displays in the middle of the room. So, in many of the storefront galleries that are so common in small towns and crowded downtown areas, art and photos are going to be viewed from close-up, no matter how big they are printed.

The same is true for most homes. The biggest room in my house is 17 feet by 15 feet, and my house is of the average, typical size and layout that you find in the neighborhoods here in my town. If I put a print on any of my walls, I would be viewing it from a distance of 4 to 11 feet. Am I going to intentionally look for places to stand that put me further back? Of course not. I am going to view things from where I am, and would not go out of my way to view them from an inconvenient position, just so that I don't notice the lack of detail in the print. Instead, I will take a print with more megapixels, so that I can view the prints from a normal, comfortable position, and enjoy seeing all of the well-resolved fine detail that my camera was able to capture. How can one give "attention to detail" if the detail is not even there?

Wilt wrote in post #16289401
And it requires three pixels to represent a line pair, so you need three pixels within 0.012528" in order to represent a line pair that the eye could detect.

You should actually calculate with two pixels to represent a line pair.

Three pixels are needed for black-white-black.
Five pixels manages black-white-black-white-black.
Seven pixels manages black-white-black-white-black-white-black.

So it grows with only two pixels for every new line - not three.

pwm2 wrote in post #16289589
You should actually calculate with two pixels to represent a line pair.

Three pixels are needed for black-white-black.
Five pixels manages black-white-black-white-black.
Seven pixels manages black-white-black-white-black-white-black.

So it grows with only two pixels for every new line - not three.

Yeah, you're right. Number of lines represented by N pixels is (N/2)+1

Post 81 is now corrected...160 pixels per inch meets human visual acuity for 24x36" print viewed from 36"

Much better thread than most of the 'how many MP do you need'. Personally I find that everything else being equal, 15-18 is about as low as I'd want (i.e. if Canon bought out an 8MP camera with the DR of a D800, I probably wouldn't' bite).

However, I remember my first digital camera, a P&S with 2MP and I wondered why I hadn't switched from film years earlier. For what I wanted, it was better than film.

To me it's like asking if a lens is 'sharp'. A lens is sharp enough if it does the job, what's sharp to one person is soft to another. I remember someone saying he thought the 135L was kinda soft with poor bokeh, well he was comparing it to the 200 f2. For many a kit lens is way sharp enough.

I'd never tell someone that a lens is sharp enough for them any more than I'd tell them that X MP is enough or more than they need. It's like telling someone that they don't need a car that can do more than 80mph or is larger than can just fit their family.

I don't care that Jo Blogs won't notice the difference in one of my prints at 5MP vs 18MP. I'll notice, and that's important to me. I want to walk up to my prints and look at them closely and remember what it was like being there. Nobody can tell me what is good enough for me.

And that 2MP P&S was just great!

Wilt wrote in post #16289248
Pardon, I was assuming someone with 20/20 vision below the age of 40 when the arms become insufficiently long for reading!

Well, I was kind of joking, I'm 25, scored 0 on the x-rite hue test, and only have -1 vision, so I don't even feel the need to wear glasses unless I'm at the movies.

That said, a photographer will make any excuse to leave their nose print on prints, so no need for "equivalency" figures here, they are meaningless for anyone except non-photographers.