Dual ISO FPM test on the 100D at the maximum 2520x1080 resolution with the 8 ... 11-bit losslessly compressed mode
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There are several reasons why this 5x-magnification high-resolution mode would be very interesting to use with Dual ISO. Here are a few:
1) At low ISO (100 and 200 ISO), it provides very high video quality (a lot of fine detail, beautiful colors, smooth tone transitions, excellent dynamic range, etc.) which makes it ideal for shooting landscape videography, smooth timelapses, etc.
Even at high ISO-values, if the scene is properly exposed, the results are quite satisfactory. I often film at ISO 800 and 1600 with the 100D and am quite satisfied with the image quality. Here is a frame grab from a clip from this morning that I shot at ISO 800:
On this photo, I deliberately pushed the shadows a little bit in ACR to create an impression of the noise in the dark areas. As you see, the noise is monochromatic, (see the TV set), meaning that it can easily be reduced in post to pleasing levels without degrading fine detail too much.
2) When shooting events in rooms and halls that are not well lit, (e. g. people dancing under lights hanging from the ceiling), the background that occupies a large area of the frame, is often too dark. When you try to push the shadows a little bit to let some more detail come up, the noise becomes too intrusive as shown in the above photo. In this case, if the clip is shot at Dual ISO, the noise in the dark areas of the clip may be greatly enhanced. The same applies also to high-contrast landscape scenes, city light videography at night, etc.
For these reasons I decided to check out Dual ISO in that mode too. For the test I shot the same scene at exactly the same camera settings but at Dual ISO 800/3200. Then I applied MLV_Dump and CR2HDR to get the final result and applied a few corrections to it in ACR to match the photo from #1. Here is the result:
On this photo, despite the fact that the high-ISO setting is 3200, the noise on the TV set is almost identical to the one from the previous photo shot at ISO 800. This means that the Dual ISO technique has 2 stops potential for improving shadow noise in videos shot in this mode. No focus pixels are visible (excellent work, Dfort !!!) Unfortunately, there are other artifacts visible in the photo but they have nothing to do with the focus pixels. We have now overexposure in the highlights and, therefore, magenta colorization on those areas (see the wall). Also Dual ISO horizontal lines are clearly visible on the overexposed areas. Those lines were visible on the frame grab right after the CR2HDR processing, so they do not have anything to do with focus pixels either.
My impression is that the above artifacts are caused by the quite extreme Dual ISO settings of 800/3200 that I had to use for this clip due to the dim light. This probably caused reduction of the dynamic range and overexposure of the highlights. To verify this, I shot another clip of a much better lit scene where I used Dual ISO 100/800. The CR2HDR procedure reported 11,5 stops dynamic range on that frame. Here is the result:
Here we see some small focus pixel residues in the highlights but basically, the result matches the one obtained by Dfort here:
https://www.magiclantern.fm/forum/index.php?topic=16054.msg195983;topicseen#msg195983As he demonstrated, these can be fully removed by adding some chroma smoothing. There are other artifacts that could be more of a concern. They appear along the edge of the cupboard, on the frame of the painting and on the plant in the background. I am not sure what their origin might be but they could also be lens related.
CONCLUSIONS:
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Dfort and Boncyball have done a hell of a job in removing focus pixels in the losslessly compressed modes of the 100D. The resulting video clips are very clean and free of focus pixels up to the maximum resolution of 2520x1080. Even Dual ISO works well at this resolution and provides fairly clean results. Care should be taken to not use too extreme Dual ISO settings and to properly expose the scene. Overexposure in the highlights should be avoided. Further tests are necessary to see if the Dual ISO technique will prove usefull in real-life filming conditions but if yes, this is another reason why the quite annoying "hick-up" issue that appears with moving objects in this mode should be fixed. Nikfreak, you are our last hope in that respect ... !
