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09-28-2011, 11:02 PM   #1
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Request - K5 Bracketing at night

Good Evening Everyone,

For the last couple of months, I have been sitting here watching the K5's prices and trying to decide what to do. I usually shoot in the late afternoon and early evening - ambient low light, and at times use bracketing (usually 5 frames) in order to capture the blue sky after sunset. This time of the year from about 6pm (after work) to sometimes as late as 9pm (yes - its dark). Currently using a K20, and I know that the K5 has a much better dynamic range, and even ISO 80. So my concerns are:
  • Taking a 5 frame bracket at say 2 ev between frames. My frames during one of these 5 frame brackets run from .5 seconds to 30 second exposures (and DFS kicks in). What I usually get when I stack is noise in the 2 -ev frames. When I look at the frames in Bibble pro 5 or Elements, they look just fine. When I take a look at them with Picasa - I get noise (and yes I know that Picasa pushes the images - thereby just amplifying the latent noise), however when I stack with any of the stacking/stitching utilities I get the noise, so by using Picasa it provides me a good indication of what I will probably wind up with.
Is anyone seeing anything like this from their K5 - specifically noise when they stack?

I have posted this before, but this is what I am trying to accomplish (and these have had the noisy frames removed, so they would not bleed through into the final result)....

This was taken at 10mm with my 10-17. I have very carefully added a CZ 28/2.8, CZ 85/2.8 and Auto Tak 28/1.8 to complement my 31 Ltd and 12-24, to work with opportunities like this. However, I'm feeling the need for a body to complement the lenses, that will suppress the noise at low ISOs - I shoot at 100.



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Last edited by interested_observer; 09-28-2011 at 11:41 PM.
09-29-2011, 06:01 AM   #2
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Can you explain your workflow - eg. when you say 'stacking' are you referring to exposure blending, or HDR creation? Are you using RAW images or JPEGs? How are you metering (spot, center-weight, etc.), and what are your shutter times?

I haven't used Photomatix, but in my experience if you're getting noise in the resulting image, it means that you have underexposed areas on your +4EV image. In many of the shots I've done, I run into the timer limit of the camera (30s max) and need to use bulb mode to get the dark areas exposed properly. If you have the RAW image of the +4, can you post it somewhere?
09-29-2011, 07:58 AM   #3
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Morning and thanks for the comment and question. Yes, when I bracket I usually more often than not, have at least 1 if not 2 frames of the 5 frame brackets that are severely - very underexposed (black with the exception of some of the brighter points of light - and I expect that). I shoot RAW at ISO 100, and sometimes 200 so as to hold down the exposure times. Unless there is some very specific reason, the metering mode is multi-segment/pattern. I do this so that I get a general average of the available ambient light across the frame, rather than just a single point to meter off of. To tell you the truth, in the early to late evening, I am really scratching for ambient light. I do know that I am at the extreme margins here. My exposure times are, using one set as an example, @ f 3.5 using AE mode (0 ev, 3 sec), (-2 ev, 0.5 sec), (+2ev, 10 sec), (-4 ev, 1/8 sec), (+4 ev, 30 sec). The underexposed frames are the -2 ev and -4 ev.

I usually tone map or HDR - just wanting as natural look as possible. I am not really trying to go to any extreme with the results. I am not looking for a daylight feeling, and since its in the evening, and I am looking for some what of a dark valley lights/city lights appearance. In the example shown, I want to try to catch the city lights, illuminating the mountain sides there in Sedona.

What I have been doing, in order to get around this problem is to shoot multiple sets of 5 frame brackets with ev intervals of 0.5 ev, 1 ev, 1.5 ev, and 2 ev, so in theory I take about 4 sets of 5 bracketed images or about 20 frames. This way I have sufficient frames to make selections (essentially eliminating the noisy frames which would be the -ev frames if they bring in too much noise) from to stack and or stitch (or sometimes both).

I need to run off to work to catch a meeting. I'll find a site to upload a 5 frame set this evening. Or if you can suggest a site, I'll use your suggestion.

09-29-2011, 09:41 AM   #4
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Wow - at ISO 200 and f/3.5, you should have no trouble capturing the entire DR of that scene. I typically shoot f/8 or f/11, ISO 100 - occasionally I'll need an extra shot in bulb mode (2 minutes or so). I usually shoot 5 exposures, 2EV apart, but I shoot manual, with my 0EV image at 2 seconds (which means that the +4EV image is 30 seconds, which is the longest you can get without bulb).

I don't think that shooting extra "intermediary" shots at 0.5EV does much except provide a way for to average out some of the noise; as long as you capture the entire DR of the scene, the HDR generation should ignore any underexposed/overexposed areas from each image, so it's only using the workable range. The underexposed images should only be used for the highlights.

I look forward to seeing the originals; the only file-storage site I've used was adrive.com - seemed to work OK.

09-29-2011, 12:06 PM   #5
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I have no experience in K5. But for the shadow areas you can select one of the images and manual mask. As stated if you capture the DR of the scene you wont have a problem.
09-29-2011, 06:14 PM   #6
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I uploaded a zip file containing 5 bracketed shots, all RAW .pef files. I made it public. All the EXIF meta data is intact.
As a processing example, I have used Microsoft ICE (free), just by dragging all 5 files into the application. It processes and produces noise in the lower left hand corner. I can clean it up by just dragging the frames 1, 3 and 5 into the application.

09-29-2011, 08:00 PM   #7
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OK, I got the images, and it appears that there are a couple of underexposed areas on the +4EV. I was able to generate an acceptable HDR with Picturenaut, and tone-map it with LuminanceHDR. There is a fair amount of grain, probably due to ISO 200. I've attached the picture to this post. If you like, I can put the HDR I generated and the resulting tone-mapped image somewhere for you to grab.

If Microsoft ICE is generating noise when you use images 2 and 4, then I'd say it's likely that there is a bug there - it could be trying to extract data from the underexposed areas when it shouldn't. It looks more like a panorama stitcher rather than a dedicated HDR generator, so that could be why (I've not had much luck with Hugin's HDR generation.)

If you're going to do a re-take, my recommendation would be to switch to ISO 100, and take some long exposures - 2 minutes might be OK, but 4 would be better.

For these exposures, try using Picturenaut (it's free) to generate the HDR (I used automatic alignment and color balancing on, exposure correction and ghost removal off) and something like Photomatix or LuminanceHDR (also free) to tone-map it. I recommend the separate programs as I've found Picturenaut generates the best HDR, and LuminanceHDR does the best tone-mapping, but YMMV.

Name:  ptest_pregamma_1_mantiuk06_contrast_mapping_0.3_saturation_factor_1_detail_factor_3.jpg
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09-30-2011, 06:55 AM   #8
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Hi Karl,

The result you produced is excellent - way beyond my expectations. This goes back to the first of the year, when the camera was generating nothing but noise - when I sent it in for warranty. At that time I was walking through just about all the HDR trial packages. After getting the camera back I had tried Autopano and ICE, both generating similar results - so I wound up not really going any farther. I didn't want to start trying to find the best package again, if I was taking (essentially starting with) noisy images. I have gone back now and ran some of the other packages - I already had picturenault, but not luminance, and I just ran across fusion. Actually autopano does both stitching and hdr, which is what I was originally going after. I need to figure out how to adjust autopano to not sum and amplify the noise, and with that I will be very very happy.

As I originally indicated, I was thinking about the K5. With this, I can easily continue with the K20 and slide a decision out to the K3 or whatever, maybe even a bit longer. Since this time last year, I have found, acquired and modified the CZ lenses and was getting use to using them. This valley lights location is about a 5 minute drive from the house and I use it quite a bit. The Sedona location is a 2 hour drive - one way. Since I have today off, I was going to drive up to Sedona this afternoon and take several SD cards worth of images - late afternoon, sunset, and early through the late evening. So, I will have quite a bit more material to use.

I can also go back to taking the full 2 ev steps which will help quite a bit.




Last edited by interested_observer; 09-30-2011 at 11:24 AM.
09-30-2011, 08:48 PM - 1 Like   #9
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Glad I could help. I took a look at Autopano tonight - it seems to have a hard time with autoalign on the images you gave (Hugin has the same issue, and frequently needs to have the control points done manually.)

Something I did notice is that its RAW loader greatly amplifies the noise, which may be the issue you're seeing. When I used your PEFs directly, the resulting HDR was unusable, but after I used ufraw-batch to convert them to 16-bit TIFF, Autopano produced very good results.

If you don't mind a bit of a plug, take a look at "Two lanes turn right". I used Picturenaut for the HDR generation, Luminance for the HDR tone mapping, and Hugin for the stitching.
10-01-2011, 08:10 AM   #10
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Morning Karl,

I do remember seeing your "Two Lanes, Turn Right" some time ago when it was first posted. I actually forget how I came across it. The detail that you were able to capture is incredible.

Your observation about the RAW loader actually rung a bell. 12 -18 months ago I was (and I guess, still am) looking at various packages - some of which did not support RAW (.PEF) format. So I converted the source to 16 bit TIFF so that I would have the same source available. I had a note, I see that the TIFF seemed to produce much better results in the packages that also supported RAW. I am now thinking that is at least part of the problem - if not all of it (well the K20 sensor is what it is for what I am trying to do with it - the K5 would obviously be better).

10-01-2011, 09:58 PM   #11
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Hi. Karl. I notice you are a linux user. Have you tried the HDR and stitching functions in fotoxx? I find them quite useful:

fotoxx - kornelix

Jack
10-09-2011, 10:52 PM   #12
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Can you make any recommendations for Mac HDR software?
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