Just checking - DR and film simulation modes are for jpg only?

Started Feb 25, 2013 | Discussions thread
nixda
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Re: JPEGs always compress over-exposed data - RAW releases it as it was
In reply to Trevor G, Feb 28, 2013

Trevor G wrote:

I'll just respond to this post here but also consider your statements above in the other sub-thread.

First, you are absolutely correct that my 'definition' of 'headroom' is not the right one. But see below.

Randy Benter wrote:

Nixda said "the sensor doesn't have 'headroom"

And technically, he is correct.

In practise, though, the camera maker incorporates headroom by determining where the 0EV exposure point is. Past that 0EV exposure point, all JPEGs crush further image content into just 0.3EV.

There could be another 2.7EV (as my example shows) crushed into just 0.3EV, while the image data below 0EV is also somewhh compressed as well, in a non-linear way.

and you replied "the sensor does have headroom"

In this example you are saying the same thing in different ways.

Nixda did not say that highlight headroom does not exist. He said that headroom is the difference between the data available in a raw file and a specific iteration of a jpeg file. He also said that "headroom is not an intrinsic, positive aspect of the sensor" and I agree.

We all agree on that technicality.

It's the practicality where the confusion exists, because he has chosen a private, incorrect definition of the term "headroom".

Mine is not so much a definition as it is a pragmatic view of what most photographers assume when thinking about 'headroom'. I might be completely wrong here, though, because I can't read peoples' minds. But when I see comments about 'headroom', they are usually along the lines of how I described and discussed it (see below).

You (Trevor) then gave examples of how highlights can be recovered from raw files and jpeg files, which is what Nixda said. You have posted this same example many, many times, but your explanation is always centric to both the X10 and SilkyPix.

I have posted this once? before in this forum.

Lightroom handles these files in exactly the same way.

It doesn't matter that the example is from an X10, because the relationship between RAW and JPEG is the same across the board, irrespective of camera or sensor.

I use the 2.7EV example because it makes it easier to see the compression which occurs with JPEG. The only thing I didn't show this time is the way "recovery" from an over-exposed JPEG leads to incorrect colours.

I still think we are talking about similar things here, so to get back to the not-so-uncommon usage of the term 'headroom', a statement, paraphrased, that I come across all the time:

"The JPEG was completely blown out, but when I opened the raw data and adjusted the exposure, I was able to get 3EV worth of highlights back. I love this sensor and its headroom".

To me, these people compare the JPEG with the raw data, realize that there is more information in the raw data than in the JPEG data and are excited that they were able to utilize that information. They realize that there is a 'space' that contains usable data in addition to the JPEG version, and they call that space 'headroom'. They think that space is a feature of the sensor. In addition, they also talk about 'recovering highlights' in this respect.

Wrong usage of terms, and I admit I am guilty as well, but it's often easier to use the same terms as someone else in discussions. Now, I also fully admit that the analogy to sound engineering hadn't fully sunk in, although I knew where the term 'headroom' comes from.

Thanks for explaining it rather clearly.

So, now the other thing: what do you make of DPR's >13EV 'dynamic range' where they analyze the 'Tone Curves DR 400' in the X-Pro1 review? That is still something that bothers me.

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