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What an unprocessed photo looks like

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Re: What an unprocessed photo looks like

#251

Post by skrebbel »

shagie wrote: post #101
barishnamazov wrote: post #7

I love posts that peel back the abstraction layer of "images." It really highlights that modern photography is just signal processing with better marketing. A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of t…

> A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of the luminance (brightness/detail) data. From the classic file format "ppm" (portable pixel map) the ppm to pgm (portable grayscale map) man page: https://li…

> The quantization formula ppmtopgm uses is g = .299 r + .587 g + .114 b.

Seriously. We can trust linux man pages to use the same 1-letter variable name for 2 different things in a tiny formula, can't we?

Re: What an unprocessed photo looks like

#253

Post by liampulles »

NooneAtAll3 wrote: post #234
liampulles wrote: post #216

Earlier quoted context omitted.

The bit about the green over-representation in camera color filters is partially correct. Human color sensitivity varies a lot from individual to individual (and not just amongst individuals with color blindness), but general statistics indicate we are most sensitive to red light. The main reason is that green does indeed overwhelmingly contribute to perceptual luminance (over 70% in sRGB once gamma corrected: https:…

> we are most sensitive to red light > green does indeed overwhelmingly contribute to perceptual luminance so... if luminance contribution is different from "sensitivity" to you - what do you imply by sensitivity?

Upon further reading, I think I am wrong here. My confusion was that I read that over 60% of the cones in ones eye are "red" cones (which is a bad generalization), and there is more nuance here.

Given equal power red, blue, or green light hitting our eyes, humans tend to rate green "brighter" in pairwise comparative surveys. That is why it is predominant in a perceptual luminance calculation converting from RGB.

Though there are much more L-cones (which react most strongly to "yellow" light, not "red", also "much more" varies across individuals) than M-cones (which react most strongly to a "greenish cyan"), the combination of these two cones (which make ~95% of the cones in the eye) mean that we are able to sense green light much more efficiently than other wavelengths. S-cones (which react most strongly to "purple") are very sparse.

Re: What an unprocessed photo looks like

#254

Post by devsda »

liampulles wrote: post #216
barishnamazov wrote: post #7

I love posts that peel back the abstraction layer of "images." It really highlights that modern photography is just signal processing with better marketing. A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of t…

The bit about the green over-representation in camera color filters is partially correct. Human color sensitivity varies a lot from individual to individual (and not just amongst individuals with color blindness), but general statistics indicate we are most sensitive to red light. The main reason is that green does indeed overwhelmingly contribute to perceptual luminance (over 70% in sRGB once gamma corrected: https:…

Is it related to the fact that monkeys/humans evolved around dense green forests ?

Re: What an unprocessed photo looks like

#255

Post by adrian_b »

zinekeller wrote: post #141
shagie wrote: post #139

Earlier quoted context omitted.

To the "the grandfather of all luminance coefficients" ... https://www.earlytelevision.org/pdf/ntsc_signal_specificatio... from 1953. Page 5 has: Eq' = 0.41 (Eb' - Ey') + 0.48 (Er' - Ey') Ei' = -0.27(Eb' - Ey') + 0.74 (Er' - Ey') Ey' = 0.30Er' + 0.59Eg' + 0.11Eb' The last equation are those coefficients.

I was actually researching why PAL YUV has the same(-ish) coefficients, while forgetting that PAL is essentially a refinement of the NTSC color standard (PAL stands for phase-alternating line, which solves much of NTSC's color drift issues early in its life).

It is the choice of the 3 primary colors and of the white point which determines the coefficients.

PAL and SECAM use different color primaries than the original NTSC, and a different white, which lead to different coefficients.

However, the original color primaries and white used by NTSC had become obsolete very quickly so they no longer corresponded with what the TV sets could actually reproduce.

Eventually even for NTSC a set of primary colors was used that was close to that of PAL/SECAM, which was much later standardized by SMPTE in 1987. The NTSC broadcast signal continued to use the original formula, for backwards compatibility, but the equipment processed the colors according to the updated primaries.

In 1990, Rec. 709 has standardized a set of primaries intermediate between those of PAL/SECAM and of SMPTE, which was later also adopted by sRGB.

Re: What an unprocessed photo looks like

#256

Post by jiggawatts »

pbalau wrote: post #249
jiggawatts wrote: post #80

I've been studying machine learning during the xmas break, and as an exercise I started tinkering around with the raw Bayer data from my Nikon camera, throwing it at various architectures to see what I can squeeze out of the sensor. Something that surprised me is that very little of the computation photography magic that has been developed for mobile phones has been applied to larger DSLRs. Perhaps it's because it's…

> Something that surprised me is that very little of the computation photography magic that has been developed for mobile phones has been applied to larger DSLRs. Perhaps it's because it's not as desperately needed, or because prior to the current AI madness nobody had sufficient GPU power lying around for such a purpose. Sony Alpha 6000 had face detection in 2014.

Sure, and my camera can do bird eye detection and whatnot too, but that's a very lightweight model running in-body. Probably just a fine-tuned variant of something like YOLO.

I've seen only a couple of papers from Google talking about stacking multiple frames from a DSLR, but that was only research for improving mobile phone cameras.

Ironically, some mobile phones now have more megapixels than my flagship full-frame camera, yet they manage to stack and digitally process multiple frames using battery power!

This whole thing reminds me of the Silicon Graphics era, where the sales person would tell you with a straight face that it's worth spending $60K on a workstation and GPU combo that can't even texture map when I just got a Radeon for $250 that runs circles around it.

One industry's "impossible" is a long-since overcome minor hurdle for another.

Re: What an unprocessed photo looks like

#257

Post by yzydserd »

barishnamazov wrote: post #7

I love posts that peel back the abstraction layer of "images." It really highlights that modern photography is just signal processing with better marketing. A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of t…

Another tangent. Bryce Bayer is the dad of a HN poster. https://news.ycombinator.com/item?id=12111995 https://news.ycombinator.com/item?id=36043826

Re: What an unprocessed photo looks like

#258

Post by adrian_b »

brookst wrote: post #96
barishnamazov wrote: post #7

I love posts that peel back the abstraction layer of "images." It really highlights that modern photography is just signal processing with better marketing. A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of t…

Even old school chemical films were the same thing, just different domain. There is no such thing as “unprocessed” data, at least that we can perceive.

True, but there may be different intentions behind the processing.

Sometimes the processing has only the goal to compensate the defects of the image sensor and of the optical elements, in order to obtain the most accurate information about the light originally coming from the scene.

Other times the goal of the processing is just to obtain an image that appears best to the photographer, for some reason.

For casual photographers, the latter goal is typical, but in scientific or technical applications the former goal is frequently encountered.

Ideally, a "raw" image format is one where the differences between it and the original image are well characterized and there are no additional unknown image changes done for an "artistic" effect, in order to allow further processing when having either one of the previously enumerated goals.

Re: What an unprocessed photo looks like

#259

Post by formerly_proven »

barishnamazov wrote: post #7

I love posts that peel back the abstraction layer of "images." It really highlights that modern photography is just signal processing with better marketing. A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of t…

> It really highlights that modern photography is just signal processing with better marketing.

Showing linear sensor data on a logarithmic output device to show how hard images are processed is an (often featured) sleight of hand, however.

Re: What an unprocessed photo looks like

#260

Post by bstsb »

ajkjk wrote: post #50
bstsb wrote: post #42

Earlier quoted context omitted.

hey, not accusing you of anything (bad assumptions don't lead to a conducive conversation) but did you use AI to write or assist with this comment? this is totally out of my own self-interest, no problems with its content

found the guy who didn't know about em dashes before this year also your question implies a bad assumption even if you disclaim it. if you don't want to imply a bad assumption the way to do that is to not say the words, not disclaim them

didn't even notice the em dashes to be honest, i noticed the contrast framing in the second paragraph and the "It's impressive how" for its conclusion.

as for the "assumption" bit, yeah fair enough. was just curious of AI usage online, this wasn't meant to be a dig at anyone as i know people use it for translations, cleaning up prose etc

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