[Dartmoor Dave]

It has now been stated by everyone, pixels are not used to measure size. Right, keep that in mind for the rest of this post. Pixels are not ….

So take for example an image projected on a 35mm frame/sensor and then viewed on a 24” screen.
Has the image size been reduced? (Remember, pixels are NOT a measurement of size, millimeter are.)

It has been enlarged.


If we now take an image from a APS-C sensor and display it on the same 24” screen, it has to be enlarged even more then the FF image to fill the screen. ENLARGED, even though it was down sampled. Pixels are NOT used to measure size.

The photodiode that converts the photons to electrons has a physical size, but once the charge has been measured and stored as a digital value, it's just a data point with no physical size. It isn't stored as part of an image of a certain physical size, it's stored as part of an image of a certain pixel resolution.

A line one pixel wide on a sensor does not get enlarged into a line multiple pixels wide on a computer monitor. At 100% it will appear as a line one pixel wide on the monitor, but after downsampling to fit the whole image on the screen it's entirely possible that it will just get downsampled away. Although actually downsampling algorithms are designed to try to preserve single pixel edges to retain a sense of sharpness.

The image on your computer screen is big because the individual pixels that make up the screen are big. You've now taken the data points that have no physical size and turned them into something that does have a physical size.

A digital camera sensor is a fundamentally different technology to a piece of film, and you have to be careful not to assume that they do things the same way. In many ways, the resemblance between the two technologies is so superficial that it's almost irrelevant.

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Last edited by Dartmoor Dave; 08-23-2019 at 05:29 AM.

[Gimbal]

So when my image viewer magnification is set to 100% it should show the image at the size of the sensor according to that.

What? 100% isn't a size.
It doesn’t work that way since pixels doesn’t have a commonly agreed upon size.

---------- Post added 08-23-2019 at 03:39 PM ----------

Don’t mix the number of pixels making up an image, with the size of the image. It’s two different things.

An image can be enlarged at the same time as the number of pixels used can be reduced. It is still enlarged.
A photo printed two by two meter can be down sampled to 10x10 pixels, it is still enlarged, even though pretty much all information is lost.

[beholder3]

I think all relevant inputs have been provided so that readers can understand what is right and why it is.

Having to explain again and again that enlargement happens between a 16x24mm image recorded in a camera and a print or computerscreen is too much.

[pschlute]

Having to explain again and again that enlargement happens between a 16x24mm image recorded in a camera and a print or computerscreen is too much.

But the whole point is that there is no such thing as a "16x24mm image". The sensor is not the same as a film negative. The sensor produces digital data for each pixel, but that pixel data has no physical size. I can display that image on a computer monitor or on a giant screen at a soccer stadium. Depending on the resolution of the viewing medium (and display options) will determine whether the pixels in the image are downsampled by the display software. But at no point are the pixels "enlarged". They are displayed pixel for pixel on the display medium.

[swanlefitte]

Having to explain again and again that enlargement happens between a 16x24mm image recorded in a camera and a print or computerscreen is too much.

My image of the moon is recorded using a 16x24mm device. The image is only the pixels.

[Fogel70]

But the whole point is that there is no such thing as a "16x24mm image". The sensor is not the same as a film negative. The sensor produces digital data for each pixel, but that pixel data has no physical size. I can display that image on a computer monitor or on a giant screen at a soccer stadium. Depending on the resolution of the viewing medium (and display options) will determine whether the pixels in the image are downsampled by the display software. But at no point are the pixels "enlarged". They are displayed pixel for pixel on the display medium.

Of course the image captured by the camera has a size. It is the lens together with the camera that set the size of the captured image. And every image captured has an magnification ratio, that is the ratio between the size of the captured scene and the size of the projected image on the image capturing media.

If the image captured by the camera didn't have a size it would not be such thing as a 1:1 macro shot. But every shot by every camera has an magnification ratio so it must also have a size.

[Gimbal]

But the whole point is that there is no such thing as a "16x24mm image".

Oh but there is. The image is there during the exposure, and as soon as the shutter closes the sensor starts to convert it into digital numbers. The size of the image is the same as the size of the sensor.
It's comparable to a film that is later feed through a scanner and digitized, we just skip the film part and digitize immidiately.

[Dartmoor Dave]

If the image captured by the camera didn't have a size it would not be such thing as a 1:1 macro shot. But every shot by every camera has an magnification ratio so it must also have a size.

In a 1:1 macro, an object in the real world is projected at its actual size onto a piece of film or a sensor. With film, you now have a piece of film holding an image of the object at its actual size. With a digital sensor, all you now have is data at a certain pixel resolution that you can manipulate and display in any way you want. The idea of it being 1:1 is now meaningless unless you choose to view or print it at the same size as the sensor. That doesn't mean that it IS the same size as the sensor, it just means that you've chosen to look at it at that size.

It's comparable to a film that is later feed through a scanner and digitized, we just skip the film part and digitize immidiately.

Except that once you've scanned a piece of film it's just data that you can do whatever you want with. It no longer has any physical size until you choose the size you want to view it at.

Please, please, please try to stop thinking in terms of optical enlargement. It's just numerical values recording the charge captured by individual photodiodes.

[pschlute]

If the image captured by the camera didn't have a size it would not be such thing as a 1:1 macro shot

1:1 means that the image circle from the lens projected onto the film plane/digital sensor is the same size as the actual object. It has nothing to do with how that image is recorded by digital technology.

---------- Post added 08-23-19 at 05:40 PM ----------

But every shot by every camera has an magnification ratio so it must also have a size

show me that in the exif

---------- Post added 08-23-19 at 05:41 PM ----------

The size of the image is the same as the size of the sensor

Nope. Digital sensor data has no concept of size.

[StephenHampshire]

Of course the image captured by the camera has a size. It is the lens together with the camera that set the size of the captured image. And every image captured has an magnification ratio, that is the ratio between the size of the captured scene and the size of the projected image on the image capturing media.

If the image captured by the camera didn't have a size it would not be such thing as a 1:1 macro shot. But every shot by every camera has an magnification ratio so it must also have a size.

But the image we look at is not the image on the sensor, that only exists for 1/250s, 1/2s or however long our shutter is open for. The image we look at is reconstructed from electronic data taken from the exposed sensor and stored and processed. That has no "size" except in the Mb of data sense. We can display that image with any dimensions we like, a giant print or a tiny image on a Smartphone screen

Apologies, I was interrupted whilst posting and other posts before mine make the same point

[Gimbal]

Except that once you've scanned a piece of film it's just data that you can do whatever you want with. It no longer has any physical size until you choose the size you want to view it at.

Please, please, please try to stop thinking in terms of optical enlargement. It's just numerical values recording the charge captured by individual photodiodes.

I can see your point, it's just bunch of numbers and size doesn't really matter any more.

But here is the thing, it did matter when the image was created, which means it will matter when you print it.

Lets say you have an APS-C sensor 24mm wide, you take a picture and enlarge it 20 times (just tag a long for a while) the print is 20*24=480mm wide. And you are very picky so you don't want to print bigger because noise and crap turns up.

Now take the same image with at 36mm wide sensor (of equal quality, only bigger, same exposure), and you will be able to enlarge it 20 times as well, ending up with at 20*36= 720mm wide image before the noise and crap turns up.

So size matters.

[Dartmoor Dave]

Somebody please tell Gimbal why that's wrong. It's a national holiday here until the end of Monday, and I plan on being drunk for the next 72 hours.

[Gimbal]

The center part of the printed images will be of similar quality. Perhaps even Identical.

[Fogel70]

But the image we look at is not the image on the sensor, that only exists for 1/250s, 1/2s or however long our shutter is open for. The image we look at is reconstructed from electronic data taken from the exposed sensor and stored and processed. That has no "size" except in the Mb of data sense. We can display that image with any dimensions we like, a giant print or a tiny image on a Smartphone screen

Apologies, I was interrupted whilst posting and other posts before mine make the same point

It is not the images we look at that decides the size, it is how the image was captured that do.

If you look at a large printed image, how do you know the size of the negative if you did not capture the image?

In many fields like science or automation it is very important to know the size of the captured image.

[Dartmoor Dave]

And somebody please explain to Fogel70 why that one's wrong. Along the lines of: it isn't a film negative, it's a digital data file. . .