Author Topic: Dual ISO foto - strange result after processing on OSX  (Read 3126 times)

MojoMC

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Dual ISO foto - strange result after processing on OSX
« on: August 13, 2014, 12:49:42 PM »
Hello,

I tested Dual ISO (with ETTR) on my 50D.
All pictures I am going to show are not altered, just developed with PS CC 2014, shrunk and saved as jpeg - but they show the problem.

First, a comparison shot without Dual ISO:
http://666kb.com/i/cqwk1wtjxwozsfw9n.jpg
I think in this lighting situation Dual ISO should show an improvement.

The next picture is how the unprocessed CR2 looked:
http://666kb.com/i/cqwk2aoz86pp68f8b.jpg
Seems normal, interlaced and all...

And this is how the resulting DNG after conversion looks:
http://666kb.com/i/cqwk2jgwfl1mw62aj.jpg
Compared to the examples for Dual ISO I don't see any improvement.

I used
- dcraw 9.19 from OSX_cr2hdr.zip
- exiftool from OSX_cr2hdr.zip
- cr2hdr.app 2.0 from from OSX_cr2hdr_app.zip

Logfile:
Code: [Select]
    1 image files updated
cr2hdr: a post processing tool for Dual ISO images

Last update: 2f4e2df on 2013-12-02 17:45:36 UTC by alex:
cr2hdr: fix DNG compression under Windows

Active options:
--amaze-edge    : use a temporary demosaic step (AMaZE) followed by edge-directed interpolation (default)
--cs2x2         : apply 2x2 chroma smoothing in noisy and aliased areas (default)

Input file      : IMG_0731.CR2
Camera          : Canon EOS 50D
Full size       : 4832 x 3228
Active area     : 4770 x 3177
White level     : 12500
Black borders   : 62 left, 51 top
Black level     : 992
ISO pattern     : dBBd GBRG
Noise levels    : 6.04 19.04 20.84 6.84 (14-bit)
ISO difference  : 4.04 EV (1644)
Black delta     : 2.76
Dynamic range   : 10.90 (+) 9.11 => 13.15 EV (in theory)
Looking for hot/cold pixels...
Hot pixels      : 3393
Cold pixels     : 863
AMaZE interpolation ...
Amaze took 3.60 s
Edge-directed interpolation...
Semi-overexposed: 9.85%
Deep shadows    : 49.66%
Horizontal stripe fix...
Full-res reconstruction...
ISO overlap     : 3.9 EV (approx)
Half-res blending...
Chroma smoothing...
Building alias map...
Filtering alias map...
Smoothing alias map...
Final blending...
Noise level     : 4.31 (16-bit), ideally 4.28
Dynamic range   : 13.38 EV (cooked)
Black adjust    : 0
Output file     : IMG_0731.DNG

Any ideas if something went wrong or did I misunderstand something?

jpaana

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Re: Dual ISO foto - strange result after processing on OSX
« Reply #1 on: August 13, 2014, 01:34:52 PM »
Dual ISO images usually require some exposure adjustment due to the way cr2hdr reconstructs and scales the 16-bit data from two 14-bit images. The main benefit is that the shadow areas are cleaner and hold better when exposure is increased. So some exposure/highlight/shadow adjustment is almost always needed.

MojoMC

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Re: Dual ISO foto - strange result after processing on OSX
« Reply #2 on: August 13, 2014, 01:53:58 PM »
Dual ISO images usually require some exposure adjustment due to the way cr2hdr reconstructs and scales the 16-bit data from two 14-bit images.
I was under the impression that the combining of the two exposures via cr2hdr results in an image with correct highlights and correct shadows.

But I searched some more and found an example where the exposure was adjusted quite heavy, so I tried a very quick adjustment with:
- Exposure +3
- Highlights -100
- Shadows +100

The result is clearly better; the sky is not blown and the shadows are lighter:
http://666kb.com/i/cqwlgt772bq7lt6vv.jpg