Noise, megapixels and downrezzing

[futureal33]

Morning all,

Ok I am totally confused by all this, so please allow me to explain what I think is confusing me, then hopefully someone will be able to help me get it!

Part 1.
In basic terms... if you have two cameras. One is 12mp one is 16mp. The noise level at ISO 1600 produced by both is the "same".

You open both in photoshop - and zoom in to 100% on them. At this level, the noise on the 16mp image appears worse than the 12mp image.
You then downres the 16mp image to the same size as the 12mp and suddenly that image becomes a lot cleaner than the "native" 12mp image. In my head, this means that the original 16mp image was better because you can reduce the image size if it is too noisy?

Part 2.
Printing - how would all this affect printing. Assuming I am printing something A4 size...I have the same two images, 12mp and 16mp (forget down ressing for this bit) both with the same noise level at ISO 1600. Would the 16mp look cleaner than the 12mp image printed?

I guess what I am trying to figure out, is if two camera's produce two different file size outputs (12 and 16mp) and both look the same at full size image display, but then at 100% zoom they both look different (ie, one is noisier than the other) how important is this? If they both look the same at full size, but one is 16mp and one is 12mp does that mean that the 16mp is the better image to work with?

Sorry if this all sounds confusing, but I am just struggling to get my head around this, and think the 100% thing is throwing me!

Cheers

 

[arad85]

100% means 1 pixel per screen pixel. If you had a 16Mpixel screen, when you went to 100%, the 16Mpixel image would be larger than the 12Mpixel image at 100%. When you are viewing them at "full size" (whatever that means) you are making them the same size.

It's hardly surprising that if you magnify an image more, you can see more of its imperfections.

The difference in noise is as likely to be sensor technology improvements as anything else. And if one looks cleaner when viewed at the same size (and not 100% which is making the pixels the same size, not the print) then it will print more cleanly.

 

[futureal33]

100% means 1 pixel per screen pixel. If you had a 16Mpixel screen, when you went to 100%, the 16Mpixel image would be larger than the 12Mpixel image at 100%. When you are viewing them at "full size" (whatever that means) you are making them the same size.

It's hardly surprising that if you magnify an image more, you can see more of its imperfections.

The difference in noise is as likely to be sensor technology improvements as anything else. And if one looks cleaner when viewed at the same size (and not 100% which is making the pixels the same size, not the print) then it will print more cleanly.

Thanks for the reply
So, how does 100% relate to print? If one looks more noisy at 100% zoom, but is a 16mpx image, how would that print compared to the same image off a 12mp camera at the same noise level?

Thanks

 

[arad85]

Thanks for the reply
So, how does 100% relate to print?

It doesn't. When you print, you are magnifying the sensor area to a given print size. The image from two cameras with the same sized sensor but one with 12Mpix the other with 16Mpix have to be magnified the same amount for a given print.

When you view at 100% you are making the sensor pixels the same size (the size of the pixels on screen). That has nothing to do with printing a photo at 10 x 8 as the 16Mpix image is magnified more than the 12Mpix image.

Generally (assuming a well exposed image) you will not be able to tell the 12 and 16Mpix images apart when printed (unless there is something in the image which demands the higher resolution of the 16Mpix sensor AND the lenses in front of it can resolve that detail AND you print large enough to see that detail).