Does "Gamma Correction" harm JPEGS quality?

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Originally Posted by Rent

Up to now nobody has answered the original post

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Probably because its one of those questions that's not that easy to answer, especially when the word "harm" is used. It's also something that is likely done so rarely, no one here really has a ready answer. But like many threads it will take on a life of its own.

Any change made to a jpeg is permanent, so if this is considered to be harmful because it is irreversible, then the answer would have to be yes.

On the other hand, gamma is assigned and "baked in", just like the white balance and colour space when the raw data is converted into an image format, like jpeg or tiff. Offhand, I can't find any place where I can change the gamma in the editing software I use (raw data has a gamma of 1), so I'm not even quite sure how I would do this. Microsoft systems default to 2.2 and in the past, I believe Apple went with 1.8, but in the more recent operating systems they also use a 2.2 curve.

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Originally Posted by GrumpyDiver

Any change made to a jpeg is permanent, so if this is considered to be harmful because it is irreversible, then the answer would have to be yes.

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You don't change/edit a jpg. That's a very essential thought and a reason why I draw that flow. All the editing is done on the RGB raster image in memory.. Without accepting that you get all kind of strange discussions.

About the gamma, well I always thought it's a property of the monitor. Reading your reaction I think you think so too.

George

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Originally Posted by GrumpyDiver

Offhand, I can't find any place where I can change the gamma in the editing software I use (raw data has a gamma of 1), so I'm not even quite sure how I would do this. Microsoft systems default to 2.2 and in the past, I believe Apple went with 1.7, but in the more recent operating systems they also use a 2.2 curve.

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Just to note that Apple used a gamma of 1.8.

I assume that "the gamma" in this thread does not apply to the so-called "gamma correction" that lurks in color space definitions such as sRGB, ProPhoto, etc.?

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Originally Posted by george013

You don't change/edit a jpg. That's a very essential thought and a reason why I draw that flow. All the editing is done on the RGB raster image in memory.. Without accepting that you get all kind of strange discussions.

About the gamma, well I always thought it's a property of the monitor. Reading your reaction I think you think so too.

George

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George - I think we are splitting hairs a bit here, but from a technical standpoint, I agree.

The edit is not done on the jpeg, but rather to rasterized data that was read by the editing program that came from the jpeg file. If we take that edited data and overwrite the original file (which is not correct either as what we do is delete the original file and write a new one with the same file name).

However, semantics aside, the end result is the same. The saved version with a different gamma applied to it will be a permanent record of what we did in the editing software, and unless we have saved a copy of the old file, there is no way of reversing the changes, given the "lossy" compression process used in creating a jpeg.

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Originally Posted by xpatUSA

Just to note that Apple used a gamma of 1.8.

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Thanks for catching my typo; it has been corrected.

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Originally Posted by GrumpyDiver

Thanks for catching my typo; it has been corrected.

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Whatever it is, it's a correction on the non-lineair behaviour of the old tube monitors. A behaviour that is incorporated in now a days monitors for backward usability. So far as I learned.

George

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Originally Posted by Shanghai Steve

But neither I nor Roy nor almost anyone else who is keen to keep photography as a record of what was in front of the camera at the time of capture, would object to, say, cropping or straightening.

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I suggest you re-read Roy's original posting, as that is what I was commenting on. Here is the relevant part:

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Originally Posted by Rent

What is wrong with your RAW file or your JPEG for that matter that you think it needs altering ? You will gather that I am anti post processing as far as possible. The camera should be able to give a reasonable result. Try to keep everything simple. ( Please don't take any offence at my remarks, they are made with the best intentions )

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The main reason for my initial response is that raw files ALWAYS need post-processing, as they do not look great straight out of the camera. Little things like sharpening, contrast, white balance that happen in camera when jpegs are created must be done in post for raw data.

The other issue is that raw data is usually 14-bit these days, not the 8-bit data in jpegs, so there is a lot more subtlety that can be drawn out of a properly post-processed raw file than you can ever get out of a jpeg.

To me, drawing out this data is post-processing. I'm not sure what else to call it.

As for the "camera producing a reasonable result", that is very much up for debate. I know that wedding photographers, sports photographers and event photographers often shoot SOOC jpegs for their final product, simply because the results are "good enough". These photographers do work under tight time deadlines and really don't have time to do much else.

On the other hand the wildlife photographers, product photographers, landscape photographers, macro shooters, "fine art" photographers, etc. tend to do a lot more PP work. Focus stacking, time blending, HDR, panoramic shots are all done using PP tools. In fact, you could not get the results that we see without turning to these specialized techniques. Not everyone cares for the results, but they allow photographers to work around the limitations that their cameras have.

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Originally Posted by Shanghai Steve

However, manipulating images to misrepresent reality does cause psychological harm to millions of girls and women exposed to manipulative, un-natural images of already gorgeous humans who have been photoshopped beyond all possible human perfection, simply to increase profit for multi-billion dollar companies. This has been proven to cause human suffering and it is wrong. Unequivocally harmful and wrong.

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I can't argue with that. Deliberately misleading people for gain is not ethical behaviour, but I would also extend that to the makeup, the cosmetic surgery, the clothing and the lifestyle moods that are created by these advertisers. To me the issue is the message, not the tools used to create those messages. Blaming Photoshop is an easy target, but in my view not quite on target.

On the other hand, I don't see the same negative reaction to advertising for cigarettes, alcohol or gambling, which I suspect cause even greater harm to people than some of the fashion shots do. I'm more than willing to bet that the same tools and techniques are used to sell those products as well, yet I don't hear you complaining about those images.

I think what people are forgetting is that when we blame others for our own shortcomings or the shortcomings of family members (daughters who might be influenced by fashion photos, for instance), we should also look at ourselves and ask if we have used / taught critical thinking so that they can see through how advertisers (and others) are trying to manipulate us. It is all too easy to blame the advertisers and Photoshop and all too easy to suggest that our negligence in not thinking are every bit as much to blame.


With regard to your internet issues - I suspect this might be related to how the internet in your part of the world connects to the rest of the world. I have not been to China in over 10 years, but remember having a lot of problem connecting at that time. Often, I could not even get at my own emails. I spent two months in India earlier this year and in spite of being in the "high tech capital of India - Bangalore), the internet connections, especially back to North America were horrible at times and I was getting time out issues (not the same as yours) to CiC.

I'm going to try to keep this short and civil.
I did not choose to give the advertisers of other products a free pass.
I believe that you are deliberately confusing and obfuscating the very obvious ethical position I have made.
I believe that you are deliberately and callously missing the point.
I fundamentally disagree with your reasoning that a 13 year old girl with body dysmorphia who is starving herself to death should be considered at fault for not being clever enough to see through advertising or that her parents are to blame.
I am shocked at your lack of compassion.
I believe it is best that I stop typing now before I say something I might regret.

So, since there are some images in popular culture that are altered in post in ways that you find objectionable any post-processing beyond cropping and straightening is bad? Seems a bit extreme to me.

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Originally Posted by Didace

So, since there are some images in popular culture that are altered in post in ways that you find objectionable any post-processing beyond cropping and straightening is bad? Seems a bit extreme to me.

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I'm lost, what post are you responding to?

Ted see Manfred's post #27 then Shanghai Steve's reply post #28 to Manfred's post.

Cheers: Allan

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Originally Posted by Polar01

Ted see Manfred's post #27 then Shanghai Steve's reply post #28 to Manfred's post.

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Thanks, Allan,

In that case . . .

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Originally Posted by Didace http://cdn.cambridgeincolour.com/for...post-right.png So, since there are some [but not all] images in popular culture that are altered in post in ways that [Shanghai Steve] finds objectionable . . .

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. . . . the following is a non sequitur, is it not?

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. . . any post-processing beyond cropping and straightening is bad?

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Seems a bit extreme to me.

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Only the non-sequitur seems extreme to me. :D

Having read many of the posts as this thread has developed, my contribution is to comment that this thread seems to have lost its way and perhaps the time has come for it to come to an end.

Having been insulted by Manfred ( #12 ) and having followed this thread to see if an answer was forthcoming ( it hasn't) I feel that from now on I shall read the forum but will not contribute any more
Roy

I've read this thread with increasing irritation.
I understood the initial question, and for me gamma is a 'technical issue not a moral or ethical matter. Accordingly, I expected intelligent technical discussion of a slightly esoteric question.

Instead the thread has been hijacked into childish, (no apology for this!), petulant and abusive comment regarding wider societal issues about how photography can be misused. These comments have no relevance to the original question and from my point of view, border on trolling.

I've noticed that a trend to do this has developed across quite a number of threads this last few months.

I'm quite happy to discuss the ethics/morality of photography in the context of a genuine interest in such issues. However, mereticious introduction of such issues into unrelated threads is unacceptable.

I am not interested in the bombastic opinionated and the frankly bullying tone that many threads seem to be attracting recently.

A request to the Moderators.... maybe we need an option for tag such responses as 'not liked or inappropriate'

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Originally Posted by zereshk

Hi. I am trying to understand "gamma correction" . I tried to simulate gamma correction process with photoshop but the result was terrible. first I opened a raw file and applied 2.2 gamma and saved it then opened it agian and applied 0.45 but result as I said was not good. Now could someone pleas tell me if gamma correction harms image quality or not?

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It is obvious because you said "was not good" that your use of gamma corrections harmed the image quality.
So regarding your image and treatment of it the answer is yes....:eek:

I am rather intrigued at the number of threads started by first time posters asking an unusual question and then not making any further contribution or asking follow up questions.

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Originally Posted by zereshk

Hi. I am trying to understand "gamma correction" . I tried to simulate gamma correction process with photoshop but the result was terrible. first I opened a raw file and applied 2.2 gamma and saved it then opened it agian and applied 0.45 but result as I said was not good. Now could someone pleas tell me if gamma correction harms image quality or not?

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Out of interest, I exported a raw file out of RawDigger as a 16-bit TIFF with no gamma, as in gamma = 1.

Then I converted the somber-looking TIFF to a JPEG (gamma still effectively 1).

In RawTherapee, I applied a tone curve to the JPEG so as to simulate an applied gamma of 2.2.

No "harm" was done to the JPEG - which now looked right on-screen as opposed to too dark.

Therefore, the method used by the OP was incorrect. :D

I blame Adobe ;)

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Originally Posted by xpatUSA

Out of interest, I exported a raw file out of RawDigger as a 16-bit TIFF with no gamma, as in gamma = 1.

Then I converted the somber-looking TIFF to a JPEG (gamma still effectively 1).

In RawTherapee, I applied a tone curve to the JPEG so as to simulate an applied gamma of 2.2.

No "harm" was done to the JPEG - which now looked right on-screen as opposed to too dark.

Therefore, the method used by the OP was incorrect. :D

I blame Adobe ;)

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That makes sense Ted.

The problem is really with the original statement / question. Gamma is "baked in" when the raw data is converted to an image format. A parallel situation is WB - that too is "baked in" at that stage of the process. Taking an action that is similar to changing the WB in a jpeg; you can make it "worse" or you can make it "better", depending on what steps you take in manipulating the data; depending on what you started with.

Gamma correction has nothing to do with the human visual response to light. Gamma correction is simply used to ensure the image is properly displayed (i.e. the same relative intensities that are in the real world appear on the displayed image). Quite simply, since the display device has a built in gamma, the image must have a pre-gamma to ensure an overall linear response. Without gamma correction the system response would not be linear. The eye response to light is inherently non-linear and always sees light in a non-linear manner regardless of gamma.