2 sensors in theory?

Detailed yet simple. ummmmmm.

Showing a photo of this is impossible because in time as sensor resolution has increased so has technology that overcomes the increase in noise that cramming more resolution causes. So things like new 21mpx sensors have little micro lenses to ensure less light is reflected off the surface of the sensor and such things. Really all I can do is try and dumb down astrostu's post.

Physics states that there's an uncertainty in how you count photons (particles of light) and this is based on the square root of the number of photons collected. Larger pixels collect more photons. The square root function forms a smaller percentage for a higher number so:

Photons -> Sqrt -> Percentage of Sqrt related to Photons (the noise).
4 -> 2 -> 50%
25 -> 5 -> 20%
100 -> 10 -> 10%
10000 -> 100 -> 1%

etc. So as you collect more light, the uncertainty of what you collect reduces. This is not taking into account any other noise sources which are introduced by electronics etc. So a smaller resolution gives dramatically less noise. Less noise = more fine detail visible, especially as noise goes up when you increase the sensitivity of the camera.

Remember when you reduce resolution you a reducing all the extra fine detail you recorded (assuming you recorded) so that all is left is the question of is noise. This doesn't work the other way of course. Taking the 10mpx image and increasing it to 20mpx will produce an image with notably less detail, but still notably less noise.


Wow I think I complicated it not made it better :S
 
So a smaller resolution gives dramatically less noise. Less noise = more fine detail visible, especially as noise goes up when you increase the sensitivity of the camera.

Remember when you reduce resolution you a reducing all the extra fine detail you recorded (assuming you recorded) so that all is left is the question of is noise.

ok.thanks.i understand what you mean. so if we take 2 cameras- canon 30d(8.2mp) and 7d(18mp) and print onto A4 at 300dpi (2490x3510=8.7mp) so we don't really need to resize the 30d but we need to reduce the 7d-

then the photos will show the same amount of small detail if the noise is the same.then if we print on A3 and resize the 30d then the 7d will show more fine detail.

you say 'when you reduce resolution you reduce all the extra fine detail you recorded'.what happens to it?it gets visibly smaller or goes?
 
The higher megapixel chip will have more fine detail than the lower resolution chip assuming:

IF you have plenty of light available, then noise becomes less of an issue.
IF your lens has enough resolution to support the higher resolution chip.
 
Elly you mentioned resizing but that's not the only option in this case. By resizing I am now going to assume that you mean "resampling" that is adjusting the actual image resolution to fit exactly 2490x3510. The additional detail disappears. Some may get sampled into the image so it won't look exactly the same, but all in all the detail is mostly lost.

In contrast: what you can do is print onto A4 at 455PPI (pixels per inch, not dots per inch, the dots per inch on a photo are in the order of tens of thousands). In which case the detail from the 7D gets smaller allowing you to closer interrogate the image. 300PPI is just a standard for viewing an image at arms length, it is by no means a limit of photo quality and you can print higher to preserve the extra detail.



Stosh you missed the critical part where the higher megapixel image is then downsampled back to a lower megapixel image. Where does the detail go.
 
Whoops, you're right Garbz. But Elly's last post threw me off because now we're talking about downsampling one image and upsampling the other. I'm actually now confused as to how satisfy the OP's questions.

As for "where does the detail go?" That's so much easier to see than to describe. Use any picture viewer that resizes automatically to the current window size and then just re-size your window. Then you'll see exactly how it loses detail.
 
ok.so if resized (downsized ie. for the web) the detail will be lost so the two photos should look similar but if printed the ppi can be increased to preserve the detail.

so by this you really shouldn't be able to tell the difference between a low and high mp camera from photos on the web?

u talk about 455 ppi. for the best iq would people try to use the highest ppi value they can get without downsampling the photo?or is there a standard high quality ppi value ie.455ppi.
 
Yes now you've got it. Screens are 72ppi (or 96 I can't remember) so when you resize an image to fit on the web you can't change the ppi figure, you need to resample the image (the act of interpolating data to fit in a larger or smaller resolution). But when you print you can print pretty much anything without resampling.

Think of the print of having a completely variable resolution that you can match to your photo at any time. When you print your higher resolution photo you can get a higher resolution print, but this doesn't work on a screen since you end up with a bigger photo that may not fit on the screen.

A standard high quality value is 300ppi. This standard means someone with 20/20 vision will not be able to visually resolve the pixels when the photo is held at arms length. This doesn't mean all photos need to be 300ppi or higher. If you can only just see the pixels at arms length it doesn't make it a worse photo even when printed 200ppi to 250ppi, and when you print an image that's 40" wide then you're not going to look at it from arms length anyway so much lower resolutions are acceptable.

If you show your huge 100ppi print to someone and then go pressing their nose into the picture and complain about the resolution, then they weren't looking at your picture and they don't deserve to see beautiful things (my opinion) :)
 
ok.thankyou for your help Garbz
 

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