Canon 5D Mk iii high ISO RAW file size considerations

BellissimaPhoto Photographers 1 Comment

I been thinking about the possibility of differences in images shot at high ISO settings on the 5D MK iii, in terms of how they would look when shot in the standard large RAW format (full size, 21.12 megapixels) versus the medium RAW format, which is 10.45 megapixels in size. The primary objective of this experiment was to determine if there is an advantage of one over the other when shooting at higher ISO settings. Without summarising the results in the first paragraph, there most certainly are some significant differences, and I might just apply these finding to my wedding photography. Read on…

The target subject was a collection of books resting on a table and lit by tungsten light. The camera was mounted on a tripod and fitted with an 85mm F1.8 lens, set to a constant F5.6. Images were captured at ISO settings of 6400, 12800 and 25600. These represent the three high but still usable ISO settings. Personally I do not see the H1 and H2 ISO settings being of any use so I ignored them, and likewise anything below ISO 6400 is very clean anyway. Shutter speed was 1/125th at ISO 6400, and doubled for each ISO increment. The files were converted to jpeg format in Adobe ACR, which works very well by the way.

Now one big difference in terms of the analysis is of course the vastly different sile sizes. The Large RAW image size is 5760 x 3840 pixels and the Medium RAW image size is 3960 x 2640 pixels. The results presented below compare the following:

  1. 100% crops of each full sized image.
  2. 100% crops of the large RAW file downsized to the exact dimensions as the Medium RAW file.
  3. As per [2], but this time the Medium RAW files were sharpened roughly match the sharpness of the downsized Large RAW images.
  4. The full sized, uncropped images downsized to 650 pixels on the long edge and both sharpened with my usual web sharpening procedure.

1. 100% crops of each full sized image at the three ISO settings:

Canon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO review

 

Some interesting observations of the medium RAW files versus the large RAW files:

  • they are significantly softer
  • they maintain colours significantly better. Look at the book in the lower left of each image – the colours shifts from brown to magenta, even at ISO 12800.
  • they maintain detail a lot better (look at the gap between the lower two books)
  • the appear to be less noisy

The next step is to make the same comparisons but this time downsizing the large RAW files to the exact pixel dimensions as the medium RAW files

2. Large RAW files downsized to same pixel dimensions as medium RAW files:

Canon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO review

 

Some observations of this set of images, once again of the medium RAW files versus the large RAW files:

  • they still significantly softer versus the downsized large RAW images
  • of course the colour distortion issues of the large RAW files is still present as downsizing will not affect this aspect
  • the detail in the medium RAW images is still a lot better . The gap between the two lower books shows this quite clearly
  • noise is still significantly better on the medium RAW images

Okay, so I can hear people saying that sharpening the medium RAW images will increase noise and yes it does, so let’s see the results below.

3. Large RAW files downsized to same pixel dimensions as sharpened medium RAW files:

Canon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO review

 

To my eye, the colour shift, noise and loss of detail is worse on the large RAW image at ISO 25600. Look at the nice clean gap separating the two lower books on the medium RAW image versus the large RAW image. The colour shift also becomes quite nasty on the large RAW image at ISO 25600. On the other hand, I prefer the look of the large RAW images at ISO 6400 & 12800 even with the slight colour shift. Whether the noise is better on the medium RAW images at ISO 6400 & 12800 is debatable.

Based on these results, it looks like it could be a good idea to switch to medium RAW when shooting above ISO 12800.

4. Full sized, uncropped large and medium RAW images downsized and equally sharpened:

 ISO 6400 examples. Both images look pretty similar.

Canon 5D Mk iii high ISO review

Canon 5D Mk iii high ISO review

 

 ISO 12800 examples. Once again both images look pretty similar but there is a slight “fogginess” creeping into the shadow areas in the lower left of the large RAW image, although it is difficult to see on these small samples.

Canon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO review

 

ISO 25600 examples. The “fogginess” becomes quite noticeable in the lower left region of the large RAW image. The medium RAW image definitely looks better in my opinion.

Canon 5D Mk iii high ISO reviewCanon 5D Mk iii high ISO review

 

Conclusion

These results are merely my observations and thoughts and I am not trying to claim anything or unearth some amazing facts. Please feel free to comment below and let me know your thoughts and opinions as this would be great. In my opinion, I will more than likely switch over to the medium sized RAW file setting on the 5D Mk iii when I go above ISO 12800 as the advantages in noise, colour rendition and maintaining detail outweigh the softness of the medium sized RAW images.

On a related note, for some of my other 5D Mk iii reviews looks at this Mk iii versus Mk ii  high ISO comparison and in-camera HDR test. My first real shoot with the MK iii can be seen here.

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Comments 1

  1. Alan Elliott

    Very interesting article – I have downloaded the page as I need to check it out further before actually posting any valid comments.
    Initially the last images in the ‘real world’ to me show richer colours in high RAW but I never finally print any of my processed work after ‘completion’ as I always find further adjustments are necessary the day or so after !
    I am buying a 5d Mk111 this week so will conduct my own tests on a similar nature and then compare.
    Thanks again for your time spent on publishing your results for people like me to study and learn

    Alan

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