EXR Confusion not fully resolved

Started 11 months ago | Discussions thread
Trevor G
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Re: Here's The "Party Trick" Explained
In reply to NIK11, 11 months ago

NIK11 wrote:

Trevor G wrote:

In that way it's a "party trick" in that you can get the same result by taking two separate exposures, 2EV apart, and combining them later on in HDR software.

As others have said your statement is a generalisation and undersells what EXR uniquely achieves in jpeg.

I don't think so.

I used to think like you but using it side by side with the X20 made me realise that it didn't have anything special.  Not really.

Just today I examined some X10 pics I took early last year.  They show me definitely that the minor usability advantage of EXR is blown away by its disadvantages.  That's what I found when I shot both cams together over the course of a few weeks.  My non-EXR X20 was not left wanting in the X10's wake - in fact, the opposite became obvious.

Here's some of my evidence (watch the histogram too):

1) Find the point at which DR100 doesn't over-expose

2) Check/compare RAW and ooc JPG

3) Find the point at which DR200 doesn't over-expose

4) Check/compare RAW and ooc JPG

5) Find the point at which DR400 doesn't over-expose

6) Check/compare RAW and ooc JPG

Let's see what happens:

Here is some evidence of highlight compression which causes a colour shift and loss of contrast. This isn't random, it's in every series that I have ever shot showing EXR DR.

The only way that I know of that this could occur is through curves-type compression being used to fit the extra highlights into the existing, available image space.

To my mind, that's not good for preserving image integrity; it's the reason I have never used the otherwise-excellent Fuji ooc JPEGs, especially when shooting DR400.

RAW preserves colour fidelity in highlights and lowlights; it's only when you have to fit that same highlight retention inside the available image space that problems occur.  In other words, shooting RAW can have its own set of colour fidelity issues as you deal with wide dynamic range material.

These samples were shot with EXR Hardware in operation - in other words: M size, ISO less than DR (actually, base ISO) and DR as marked.

When you correctly expose at DR100 (no sensor "tricks" involved) both RAW and ooc JPEG histograms will match quite well. The minor differences are due to a slight colour profile difference between RAW converter output (Silkypix)  and in-camera processing

When you correctly expose at DR100 (no sensor "tricks" involved) both RAW and ooc JPEG histograms will match quite well. The minor differences are due to a slight colour profile difference between RAW converter output (Silkypix)  and in-camera processing.

Mind you, the slight build-up in green and blue (and the pointed tops) towards the right hand edge of the JPEG histogram does suggest that the JPEG was still over-exposed ever so slightly - it would have been perfect at -2EV

The screenshots are from Silkypix which allows you to compare 2 images side-by-side, like this.

Note how far the red, green and blue peaks have moved over in the OOC JPEG - this causes an obvious colour shift in the sky and will potentially cause problems in other areas outside of view of this crop

Note how far the red, green and blue peaks have moved over in the OOC JPEG - this causes an obvious colour shift in the sky and will potentially cause problems in other areas outside of view of this crop.

Lowlights are still essentially where they were before.

Maybe DR400 will save the day?

They've managed to stop the blue channel from wandering off the screen (compared to DR200), but red and green are moved up again, which causes more of a colour shift = cyan skies

Unfortunately, while blue's advance to the right has stopped, red and green are still shifting up. This increases the colour shift which leads to cyan skies.  I don't like cyan skies but you are welcome to like them.

DR400 still has more highlight retention.  In theory it provides 2EV of highlight protection, but because they use curves-type manipulation to keep the highlights under 0EV in the ooc JPEGs, in the end we seem to actually get up around 2.7EV of not-so-accurate, lowered contrast highlight protection.

Oops - where's the ooc JPEG's blue channel gone? If I reduce the output level slightly we will see that it has "climbed the wall" and clipped somewhat.

Oops - where has the ooc JPEG's blue channel highlight gone?  If I reduce the  exposure by just 0.4EV we can see - once we get that "church steeple" effect we know that we have a badly clipped channel.

Hmmm...absolutely impossible to get back the clipped, blue channel infiormation - fortunately it still exists in the matching RAW file

It's absolutely impossible to get back that clipped, blue channel information unless you have the matching RAW file.  I always shoot RAW+.

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Cheers
Trevor G
Silkypix tutorials at: http://photo.computerwyse.com

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