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10-06-2019, 10:12 AM   #1
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ISO film to ISO digital

Just curious. How does the K-1II process an image as the ISO is changed? Is there a ISO standard that all camera manufacturers adhere to? I could be wrong, but I used film cameras for many years and noticed that the higher digital ISO seems to be less grainy on my K-1II than what I remember in equivalent film.

10-06-2019, 10:37 AM - 1 Like   #2
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There is no direct equivalence between film grain and digital 'grain', which is not grain at all (because there is no silver halide involved) but digital noise. Different sensors handle differently when it comes to noise, so your K-1 sensor will give different noise characteristics to another camera with a different sensor.
10-06-2019, 10:38 AM   #3
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QuoteOriginally posted by wings Quote
Just curious. How does the K-1II process an image as the ISO is changed? Is there a ISO standard that all camera manufacturers adhere to? I could be wrong, but I used film cameras for many years and noticed that the higher digital ISO seems to be less grainy on my K-1II than what I remember in equivalent film.
The two (film and digital) are done quite differently with digital done against an indefinite standard for most makes. Pentax uses the so-called Standard Output Sensitivity (SOS) process, an objective standard that is pegged to 18% gray card response. For a basic overview, the Wikipedia is helpful as might be the pertinent CIPA regulations.
Film speed - Wikipedia
...and Douglas Kerr's excellent paper on SOS vs. REI methods of assigning digital camera ISO and digital sensitivity metrics in general.
Douglas Kerr, The Pumpkin | New Measures of the Sensitivity of a Digital Camera (PDF)
FWIW, digital noise is essentially dissimilar to film grain in that film grain is part of the image and digital noise displaces the image.


Steve

Last edited by stevebrot; 10-06-2019 at 10:53 AM.
10-06-2019, 10:45 AM - 1 Like   #4
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As it pertains to image quality (i.e. graininess), there is no standard to ISO. The graininess of film was caused by the increased size of the photosensitive grains, while the noise of a digital sensor is caused by the amplification of undersampled photosites. That's a very simplified explanation, but my point is that the reduced visual quality from increasing the ISO on film and on digital is actually two separate phenomena that only happen to share visual characteristics.

In theory, ISO should be a standard only with regards to the exposure value, that is to say that any combination of lens+camera at the same ISO, same aperture (or more accurately, t-stop,) and same shutter speed, taking a picture of the exact same scene in the same lighting conditions, should technically appear to have the same level of exposure. In reality though, the ISO standard is not enforced or followed by any company, so there will actually be variations of EV level across all brands.

Digital images can be more easily processed using special algorithms that can interpret the raw pixel data to try and reduce the level of unwanted noise, and also the massively increased resolution of sensors versus film means that more sample points overall can be recorded, thus reducing the perceived size of "grain". Again, this is a massive simplification, but this means that modern digital cameras are capable of creating more acceptable-looking images at higher relative ISO levels than what was practical with film emulsions.

10-06-2019, 11:19 AM - 1 Like   #5
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QuoteOriginally posted by wings Quote
Just curious. How does the K-1II process an image as the ISO is changed? Is there a ISO standard that all camera manufacturers adhere to? I could be wrong, but I used film cameras for many years and noticed that the higher digital ISO seems to be less grainy on my K-1II than what I remember in equivalent film.
There is no comparison. Digital sensors have a base ISO which is where there cleanest image is found. Using an ISO higher than that involves boosting the signal. The tech has changed drastically over the years so today 12800 can be the same noise as a 400 ISO from 2008.
10-06-2019, 12:05 PM   #6
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And perhaps the ISO for an APS-C sensor is not directly equivalent to that for a full-frame. I'm sure some YouTuber will explain the convolutions in terms to baffle the knowledgeable and the novice alike...

DISCLAIMER:— I MADE THAT UP! IT'S NONSENSE!!! (just working on this month's post count)
10-06-2019, 12:11 PM - 1 Like   #7
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QuoteOriginally posted by StiffLegged Quote
DISCLAIMER:— I MADE THAT UP! IT'S NONSENSE!!! (just working on this month's post count)
That is a relief!


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10-06-2019, 12:44 PM   #8
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I'm sure someone will be able to sell that as the truth, StiffLegged, such are the joys of the internet. That's why it is so good to have a place like this, where sensible people really listen and talk to another and that keeps most of the nonsense out.

10-06-2019, 02:05 PM   #9
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QuoteOriginally posted by HoutHans Quote
I'm sure someone will be able to sell that as the truth, StiffLegged, such are the joys of the internet.
That's why I'm quite selective which photography channels get my attention those that concentrate on images instead of gear. There's also Gavin Hardcastle for entertainment value!
10-06-2019, 02:50 PM   #10
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QuoteOriginally posted by wings Quote
Just curious. How does the K-1II process an image as the ISO is changed? Is there a ISO standard that all camera manufacturers adhere to? I could be wrong, but I used film cameras for many years and noticed that the higher digital ISO seems to be less grainy on my K-1II than what I remember in equivalent film.
Film ISOs related to placing the image brightness range (received by the film) in the best location to suit the film. Hence negative film can tolerate overexposure through it's intolerant of underexposure. Slide film is just the opposite and overexposure will wash out the highlights. In both cases, ISO is chosen to gain the largest dynamic range or "latitude" for film. Film tends to "saturate" gradually which means highlights don't just disappear but "wash" out.

Digital image recording is a bit like positive film in that once the highlights saturate the electronics any brighter details are suddenly lost beyond some given brightness so ISO tends to place the exposure lower (compared to film) such that highlights can be preserved. As sensors have been improved, their bottom end has expanded so shadows can be captured even with reduced exposure to hold highlight detail.

To answer your question about changing the ISO, this is functionally applying more amplification to the sensor output signal. The sensor receives less light at higher ISO settings, so to compensate, the lower sensor output receives more electronic amplification. It's like turning up the volume on a radio when a voice is too low to be intelligible. When that volume is turned up, all the audio is amplified more, including unwanted sounds. This is the case with a camera sensor. More amplification also amplifies any noise present and the image is noisier. Newer sensors are less noisy so allow more amplification and higher ISOs to be applied, however an increase in ISO usually means a decrease in image quality, not only due to noise, but also color rendering and tonal scale.
10-06-2019, 04:54 PM   #11
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QuoteOriginally posted by Bob 256 Quote
Film ISOs related to placing the image brightness range (received by the film) in the best location to suit the film. Hence negative film can tolerate overexposure through it's intolerant of underexposure. Slide film is just the opposite and overexposure will wash out the highlights. In both cases, ISO is chosen to gain the largest dynamic range or "latitude" for film. Film tends to "saturate" gradually which means highlights don't just disappear but "wash" out.

Digital image recording is a bit like positive film in that once the highlights saturate the electronics any brighter details are suddenly lost beyond some given brightness so ISO tends to place the exposure lower (compared to film) such that highlights can be preserved. As sensors have been improved, their bottom end has expanded so shadows can be captured even with reduced exposure to hold highlight detail.

To answer your question about changing the ISO, this is functionally applying more amplification to the sensor output signal. The sensor receives less light at higher ISO settings, so to compensate, the lower sensor output receives more electronic amplification. It's like turning up the volume on a radio when a voice is too low to be intelligible. When that volume is turned up, all the audio is amplified more, including unwanted sounds. This is the case with a camera sensor. More amplification also amplifies any noise present and the image is noisier. Newer sensors are less noisy so allow more amplification and higher ISOs to be applied, however an increase in ISO usually means a decrease in image quality, not only due to noise, but also color rendering and tonal scale.
Thanks for that explanation. That makes sense. If I understand it, as you increase the ISO it applies a proportional current to the sensor which increases its sensitivity which would also creates more noise and it is the noise that one might call grainy?

This is somewhat off topic, but if I select a high ISO on my K-1II does it automatically increase the high noise filter? If I wanted to see more of a darker part of an image would I increase or decrease the low noise?

I did not know about exposure difference between print and slide film, that would have been good to know when using film.

It appears that there is only an approximation of equivalency between film and digital then as I understand it. It would be interesting to see photos of the same subject from different cameras and even brands using the same ISO setting.
10-07-2019, 11:06 AM   #12
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QuoteOriginally posted by wings Quote
Thanks for that explanation. That makes sense. If I understand it, as you increase the ISO it applies a proportional current to the sensor which increases its sensitivity which would also creates more noise and it is the noise that one might call grainy?

This is somewhat off topic, but if I select a high ISO on my K-1II does it automatically increase the high noise filter? If I wanted to see more of a darker part of an image would I increase or decrease the low noise?

I did not know about exposure difference between print and slide film, that would have been good to know when using film.

It appears that there is only an approximation of equivalency between film and digital then as I understand it. It would be interesting to see photos of the same subject from different cameras and even brands using the same ISO setting.
Actually the sensor just does its thing and the signal out of it is amplified and processed downstream. That is where the extra amplification is applied to increase ISO. With less light, the sensor puts out less signal so more amplification of that signal and higher ISO (and noise).

The filter which handles noise works on the lower exposed portions of the image where the output from the sensor is lower. It does about the same thing regardless of ISO setting but it's more noticeable with higher ISO because that's were you would actually see more noise. If you're using a low ISO, the noise is lower so processing has less a visual effect.

ISO in itself is a standard and should standardize the appearance of a scene taken with different cameras using the same ISO value, but in the real world, different manufactures can apply ISO somewhat differently to their brand so differences can exist. It would be interesting to see some standardized photos from different cameras relative to ISO. Perhaps someone in this forum would know of such tests.
10-07-2019, 12:46 PM   #13
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There's already a lot of great commentary on this forums that lends itself well to an in depth understanding of the subject.

If you're looking for a simpler explanation, I'll try my hand:

Consider that the two formats of photography (Film and Digital) rely on different properties. Film, like digital, is sensitive to light, but through a chemical processes rather than a digital one. That is to say, there are chemical reagents that coat film and are reactive to light. No surprises here. In black and white film, these light sensitive reagents are made mostly of grains of silver. So, if an engineer wanted to make a film more sensitive to light, they would need to add larger grains of silver to the film coating. The graininess one sees in a film photo is quite literally these grains of silver showing up, since they've reacted to the light! So, it should be no surprise that films with larger grains of silver (high ISO films) appear more grainy relative to films with finer silver grains.

The digital process works in quite a different way. On a digital sensor, what we refer to as "grain" appears as a byproduct of something called a "signal to noise ratio". An analogous effect can be found in your car's radio. Consider, when you're downtown near the radio station, the radio signal is strong (all signal, no static noise) and your tunes sound clear. But, head out to a rural area and you'll hear a lot more static (Less signal, therefore more static noise). The same is true for a digital sensor! In low light, you'll find that there is less signal (light) for your camera to detect. By amplifying this signal (high ISO values) you are lifting put all the background noise as well. That is to say, we have a lower ratio of signal to noise information. You can imagine this noise is like a form of visual static, this is where you'll see grainy images on digital cameras. So, if not visible light, what is your sensor picking up on? Invisible light! These other parts of our whole electromagnetic spectrum which we understand as light. For example, the infrared spectrum (what we feel as heat is in fact a form of light) and the Ultraviolet spectrum what gives us sunburns despite being invisible to our eyes is also light. Now, this can get a lot more complex from this point on, since both of these processes are controlled by clever ways by camera and sensor manufacturers, but for the sake a keeping it simple, just understand that the Chemical Process and the Digital Process produce their grain in different ways.

Now, this explanation is much simpler that the complete process which takes place in our cameras every day. Some parts of this explanation may be misleading as well, since there are chemical and electromagnetic processes at work in both film and digital. But, I hope that you will find that this simplified explanation is helpful in understanding the basics of your question. There are certainly more in depth explanations that can be found online and will be there for you to seek out when you're ready. All the best!
10-08-2019, 03:11 PM   #14
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QuoteOriginally posted by Gerbermiester Quote
There's already a lot of great commentary on this forums that lends itself well to an in depth understanding of the subject.

If you're looking for a simpler explanation, I'll try my hand:

Consider that the two formats of photography (Film and Digital) rely on different properties. Film, like digital, is sensitive to light, but through a chemical processes rather than a digital one. That is to say, there are chemical reagents that coat film and are reactive to light. No surprises here. In black and white film, these light sensitive reagents are made mostly of grains of silver. So, if an engineer wanted to make a film more sensitive to light, they would need to add larger grains of silver to the film coating. The graininess one sees in a film photo is quite literally these grains of silver showing up, since they've reacted to the light! So, it should be no surprise that films with larger grains of silver (high ISO films) appear more grainy relative to films with finer silver grains.

The digital process works in quite a different way. On a digital sensor, what we refer to as "grain" appears as a byproduct of something called a "signal to noise ratio". An analogous effect can be found in your car's radio. Consider, when you're downtown near the radio station, the radio signal is strong (all signal, no static noise) and your tunes sound clear. But, head out to a rural area and you'll hear a lot more static (Less signal, therefore more static noise). The same is true for a digital sensor! In low light, you'll find that there is less signal (light) for your camera to detect. By amplifying this signal (high ISO values) you are lifting put all the background noise as well. That is to say, we have a lower ratio of signal to noise information. You can imagine this noise is like a form of visual static, this is where you'll see grainy images on digital cameras. So, if not visible light, what is your sensor picking up on? Invisible light! These other parts of our whole electromagnetic spectrum which we understand as light. For example, the infrared spectrum (what we feel as heat is in fact a form of light) and the Ultraviolet spectrum what gives us sunburns despite being invisible to our eyes is also light. Now, this can get a lot more complex from this point on, since both of these processes are controlled by clever ways by camera and sensor manufacturers, but for the sake a keeping it simple, just understand that the Chemical Process and the Digital Process produce their grain in different ways.

Now, this explanation is much simpler that the complete process which takes place in our cameras every day. Some parts of this explanation may be misleading as well, since there are chemical and electromagnetic processes at work in both film and digital. But, I hope that you will find that this simplified explanation is helpful in understanding the basics of your question. There are certainly more in depth explanations that can be found online and will be there for you to seek out when you're ready. All the best!
That was an excellent reply. Would you say then that the ASA data included with a photo is kind of useless since there is no standard used especially between manufacturers? Although I mentioned this before, it would be useful if not interesting to see images of say a standard image at various ASA settings of different cameras both from the same manufacturer and from other manufacturers for comparison.

Best wishes.
10-08-2019, 03:21 PM   #15
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QuoteOriginally posted by wings Quote
That was an excellent reply. Would you say then that the ASA data included with a photo is kind of useless since there is no standard used especially between manufacturers?
Thanks! On this count I'd have to plead ignorance. I'm not sure how metadata would tie into the whole shebang, especially since people generally edit their images and push/pull the exposure. I can say however, all of the ISO 100 film I've put into my camera and all the ISO 100 digital sensitivity I've set on my dSLR's has come out looking properly exposed when shot for those settings.



.....Except Kentmere 400 film. That stuff looks BAD like ISO 200!
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