Scanning colour negatives - grain in blue sky

[LocalHero1953]

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I have now gained a reasonable amount of experience in digitising 35mm colour negative film with a digital camera. One common problem I find is excessive graininess in blue skies. This is made worse when (as I often do in Lightroom) I adjust the Hue slider away from the cyan side towards the deeper blue side. If I were to print some of these images, in many cases the grain might not be visible, but in others it is coarse and ugly enough that I'm sure it would. 

I have 'solved' this issue with the latest iteration of Lightroom by using the automatic AI sky masking tool, and reducing the Texture slider. I can be more selective in this process by using just a Brush mask.

I have been reading up on the subject as best I can on the internet. The best explanation I've seen for the excessive graininess is that, firstly, graininess is just easier to see in large areas of uniform tone and colour and, secondly, the red-sensitive layer in colour negative film is inherently coarser in grain than blue- and green- sensitive layers. By moving the Hue slider away from cyan towards a deeper blue, I am introducing more of the contribution from the red layer, and so increasing the apparent graininess.

I suspect there are people on this forum who understand film properties and behaviour much better than me, so I'd welcome any advice about it.

[wda]

Paul, are you using an Inherently grainy film to start the process? If not, why not zero your process and start again, carefully examining grain as you go. At least this would show you at what stage grain appears. I have resorted to this procedure when I detect the appearance of unwanted artifacts. 

 

[LocalHero1953]

2 hours ago, wda said:

Paul, are you using an Inherently grainy film to start the process? If not, why not zero your process and start again, carefully examining grain as you go. At least this would show you at what stage grain appears. I have resorted to this procedure when I detect the appearance of unwanted artifacts. 

 

Hi David - it was Portra 400 which showed enough of the issue that made me think about causes and mitigation, but also in Portra 160 and 800. It is worse in underexposed images, which is not surprising, but also visible when properly exposed. 

I don't want to make this out to be more of a problem than it is. If I need to do something, then adjusting texture in Lightroom does it easily. It is also visible because in LR I am often zooming in to 100%, which is rarely how it would be seen in real life.

A google search shows that this is a common concern. I found this discussion, and the explanation by 'randrew1' helpful.

I also wondered if there were artefacts arising from interference between grain and debayering a digital copy, but haven't found anything useful, so far.

I take your point about investigating. I shall try digital copies at different exposures, and using multi-shot hires copies (I'm using a SL2-S and Ampo-Macro-Elmarit-R 100mm + ELPRO)

Edited May 8, 2023 by LocalHero1953

[jaapv]

An older article, but maybe helpful:

http://www.photoscientia.co.uk/Grain.htm

[LocalHero1953]

6 hours ago, jaapv said:

An older article, but maybe helpful:

http://www.photoscientia.co.uk/Grain.htm

Thank you - very helpful - and a few links to follow up.

Despite the writer saying that increasing resolution does not help, I think he/she is referring to the increased resolution of the saved image from a fixed resolution flatbed scanner, not scanning using a higher resolution sensor. I will try multishot digitising and see what difference that makes. 

Edited May 9, 2023 by LocalHero1953

[rogxwhit]

Just to check that there is no sharpening going on by default settings hidden within the workflow - for instance if you are using jpg camera output, or processing a raw file.  If such is the case I'd be inclined to turn it off, and do any sharpening manually along with inspection at the output stage, eg after re-sizing for print.

[jaapv]

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2 hours ago, LocalHero1953 said:

Thank you - very helpful - and a few links to follow up.

Despite the writer saying that increasing resolution does not help, I think he/she is referring to the increased resolution of the saved image from a fixed resolution flatbed scanner, not scanning using a higher resolution sensor. I will try multishot digitising and see what difference that makes. 

One thing you could try is running Topaz Photo AI the beginning of the workflow to check whether it can handle film grain. 

[LocalHero1953]

1 hour ago, jaapv said:

One thing you could try is running Topaz Photo AI the beginning of the workflow to check whether it can handle film grain. 

I don't have Topaz Photo, but I've tried Denoise AI, and it makes little difference. I suspect the noise/grain doesn't conform to a pattern the AI recognises. I have not yet tried Lightroom AI noise reduction on a DNG (of a negative). It won't touch a tiff; my current workflow is to do a basic invert and crop of the scanned negative DNG file, then convert it to a tiff, so the Lightroom sliders work the 'correct' way. Trying AI noise reduction on the DNG is worth a try, just in case.

Edited May 9, 2023 by LocalHero1953

[LocalHero1953]

1 hour ago, rogxwhit said:

Just to check that there is no sharpening going on by default settings hidden within the workflow - for instance if you are using jpg camera output, or processing a raw file.  If such is the case I'd be inclined to turn it off, and do any sharpening manually along with inspection at the output stage, eg after re-sizing for print.

Thanks for the ideas. No, my camera output is in DNG, and I am zeroing out sharpness, clarity and texture. 

[jaapv]

10 minutes ago, LocalHero1953 said:

I don't have Topaz Photo, but I've tried Denoise AI, and it makes little difference. I suspect the noise/grain doesn't conform to a pattern the AI recognises. I have not yet tried Lightroom AI noise reduction on a DNG (of a negative). It won't touch a tiff; my current workflow is to do a basic invert and crop of the scanned negative DNG file, then convert it to a tiff, so the Lightroom sliders work the 'correct' way. Trying AI noise reduction on the DNG is worth a try, just in case.

Photo AI is a more advanced algorithm than Sharpen, more effective in my experience except for extreme cases. It is worth a try if it can handle random noise better. But it would be a hassle to run it through a DNG converter first - although Bridge can do that automatically during import.

[Photoworks]

Photo AI is just a unified tool of all the other Topaz offerings, In fact, you get it free if you brought all the others.

In any case, topaz and DxO do not fix film grain, it is useless.