Night Time HDR

[Gerry]

I recently shot some night time cityscapes for HDR conversion, however, when I converted and edited them, they ended up with artifacting in the final image. Is this typical with HDR or might it be caused by all the little pinpricks of blown out light in the night/city scene? I haven't experienced this before but haven't done much HDR either. They are fine if I edit the raw files individually. Thx. for comments.

[Colin Southern]

A picture paints a thousand words

(it helps if we can see them)

[Gerry]

Here are 100% crops & 1st is Non-HDR single image shot. 2nd is 3-image merge to HDR & edited. Small artifacts are visible all over HDR image with about same regularity as crop.




http://a4.vox.com/6a00fad690d5cd00040123f19ad59c860f-pi


http://a4.vox.com/6a00fad690d5cd00040123ddf10b84860c-pi

[James G]

Gerry,
I shoot a fair bit of HDR and have done some night shooting. By artefacts I'm assuming you are referring to haloing and noise.

I've found that the more extreme the contrasts in the image the more difficult it is to reduce halos, and I've also found that noise is amplified.

I pre process the bracketted RAW images to remove as much noise as possible prior to merging to HDR.

I use CS4 to process each image in ACR, changing Luminance and Colour of each image to reduce noise as much as possible and save the adjusted Raw files.
I then reopen them and merge them to create the 32 bit HDR image within CS4 (not Photomatix) and save this file. (I prefer ECR but Radiance seems to be much the same).
I then open the 32 bit file directly in Photomatix and tone map it. Once happy with the tone mapping I save to 16 bit Tif and reopen in CS4 and once again process through ACR to remove or at least reduce any noise generated from the tone mapping.

Depending on how extreme any residual halos are, I blend the 'average ' exposure back into the tone mapped image to eliminate them .

Final post proccesing for print is the usual charpening etc in CS4

Attached are a couple of examples of a night shot of a Church in Northern England that I took last autumn. The floodlighting is not as bright as in your shots, but the relatively long exposures (despite the low shooting ISO of100) did generate noise in the sky and shadows.

Using the workflow above I was able to eliminate most of the noise in the source images and was able to bring out a number of the brighter stars that were otherwise occluded by the haze from the floodlighting.





cheers,

James

[Gerry]

Very nice images, James. Thanks for sharing your extensive workflow. I am anxious to take on that process and check it out. You say: "I prefer ECR..." What is ECR?

This is the HDR image I am working on. In Sean's Night Photography tutorial he says: "I generally recommend always fully exposing the image as if it were a daytime photo..." which I tried on this shot. I had never shot that long on a night time shot before since I always thought the longer the shot the more the noise. Considering the high contrast on all the little bright lights, I presume that contributed to the artifacting in the merge process. They are not visible in the individual files. However, there does seem to be less noise than usual. Thx., again, for your comments.

I have not removed any noise yet in this file.

[James G]

Sorry Gerry, being dumber than usual, I meant to type EXR (for the Open EXR 32 bit image format).

I was getting my acronyms muddled, it was a long day yesterday and I'd been in a technical discussion earlier at work and ECR was stuck somewhere at the back of my head!