Thursday, November 18, 2010

HDR: Part II - Merge to HDR Software Shootout

In Part 1 I reviewed Unified Color’s HDR software and was extremely impressed with the results. For that review I tested many different types of challenging captures but I also took the bracketed files and used different ‘merge to 32-bit HDR’ programs to see if there was any difference in using them as a starting point for tone mapping with UC’s software. There certainly were differences. All worked but I found distinct advantages and disadvantages of using one over the other depending on what is in your original files. Here I will outline the differences of those I have tested, namely UC’s Expose, Photoshop CS5 (which is much better than CS4), Photomatix, and to a lesser extent the 32-bit file created by Nik’s HDR Efex. My tests focused on evaluating the following, Ghosting, Posterization, handling the Sun, Alignment and White Balance control of the resulting 32-bit file. Below are my findings and in many cases the differences only manifest themselves in extreme conditions but that is how I always do my testing since most software works well with the easy stuff.


Ghosting - All did well with subjects like moving water and to a lesser extent cloud movement. However, for moving people or cars Photomatix and CS5 have a leg up on their competition. The reason is that both of these allow you to select the exposure that includes the best position of the movement. CS5 takes a break in the merge process to let you either use their own tone mapping and/or manually correct for ghosting. At this stage click on 16-bit and look at the picture. If there is ghosting select the ‘ghost’ feature and then click on each of the thumbnail images until you get the desired result. Then select 32-bit and click on Okay. Photomatix is even more powerful in that you can select multiple areas in the image and select the best exposure for each selected area. This is powerful, especially for moving people or cars. Expose has a few ghosting options but nothing manual.


Posterization - UC Expose does the best job while CS5 does the worst and Photomatix is in between but closer to CS5. The problem occurs in the highlight regions of bright skies. CS5 is just really bad at this. The good news is that I figured out that with CS5‘s there is work around. Just use the ghosting feature the same way as I described above - click on each of the exposure thumbnails until the posterization disappears - the brightest exposure is typically the problem exposure and the middle exposure usually fixes things up. Then change back to 32-bit and hit Okay and you are all set.


Alignment - None are perfect but Expose and CS5 are near perfect. Photomatix and Nik HDR are good but botched several challenging captures. Perfect alignment is obviously critical since some of our bracketed images will be captured handheld but my tests were mostly with tripod mounted captures so less than ideal capture technique was not the problem. What kills me is how many HDR captures I deleted over the years using Photomatix because I couldn’t get the alignment to work.


Sun - Anyone that has seen my work knows my style often includes having the sun in the composition. The fireball, even when near the horizon, can often be several stops off from everything else. I don’t want a large white blown out fireball with harsh edges - which I consider a specialized variation of posterization. Regardless of which 32-bit merge I use this can still be a challenge in tone mapping. I found that UC’s Expose does the poorest job on the more difficult conditions and in many cases it is best to use a different merge program. After testing dozens of different compositions with the sun I have concluded this problem is less a result of the tone-mapping softwares and more a result of the 32-bit merge algorithm. Photomatix does the best job here closely followed by CS5.


White Balance - All of the software lets you select the WB setting ‘As Shot’. If you used the wrong WB for your capture you can either select the right one before the merge or if you corrected the WB in Photoshop’s ACR that change will travel along with the merge if using CS5‘s HDR Pro or Nik HDR Efex. A change in the RAW file will NOT go along with PM or Expose. However, UC’s Expose and 32-Float are the only tone mapping programs that let you adjust WB in the tone mapping stage. Nik’s has a ‘warm slider’ which helps but that is less versatile when you have weird color casts. Also, if using UC’s 32-Float, you can layer the 32-bit files in Photoshop using different WB settings for each and blend as needed - this is powerful stuff.


Other - Expose and Photomatix have the ability to batch process which can be a huge time saver. CS5‘s merge to HDR Pro accepts changes to made in their ACR converter. This means you can use a WB profile based on your camera instead of a generic one, correct for any lens distortion, and my favorite part is to minimize noise early on in the workflow. Noise is best handled in the beginning just as sharpening is best handled at the end of the workflow. ACR 6 now does a great job at cleaning up noise in my high ISO tests where I tried to use UC’s noise reduction, which is better than PM but neither could touch the results if I simply reduced noise in ACR first before merging with Photoshop.


In summary each of the merge-to-32-bit HDR programs have their own strengths and weaknesses. It is important to know how each performs in order to get the very best results. Therefore it is advantageous to have at least two different options to handle just about anything. I am a Bridge + Photoshop person. To that end I am finding that the workflow that is best for me is to use Photoshop to merge - especially if I want to first remove high ISO noise and use a WB profile based on my camera. The merged HDR is opened in Photoshop and I then use UC’s 32-Float plugin to tone map. This method is the most efficient for me and it also lets me create different versions and blend each using layers - which will be discussed in part III of this series.


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