Jan 24, 2021
CRI
by matt
A week or so ago, I had no idea what CRI was and what it meant. Having had reasonable results DSLR scanning my home developed colour negatives, I was content in my results. That was until I tried scanning some more dense negatives. The results were not good. Detail was missing and I seemed to need to tinker with red, blue and green sliders to get what I remembered was a representative image. Something wasn’t right. Then I realised – it was my light source. I’ve been using a cheap light tracing pad for all my scanning so far. Granted the majority of this has all been b&w film, so it’s not surprising that I’ve not noticed the problem before. I don’t mind b&w images looking grainy (quite like it actually) and my scanning of them was never about achieving image quality perfection. But colour film on medium format, when exposed correctly, is supposed to yield crisp beautiful colours with amazing detail. I was nowhere near.
So I found out about Colour Rendering Index and how important it is when digitising film with a light source, in particularly colour negative film (which needs to be inverted). All negative conversion profiles need to have one base assumption and that is they must assume they are working with correct colour levels in order to perform their transformation from a colour negative image to a colour positive image.
So I bought a new light source from Amazon – a Raleno LED video light with 192 LEDs, selectable brightness and colour temp. It’s an order of magnitude brighter than my current source, and it has a CRI of 95 (100 is the max). Gone is the hair pulling frustration with colours after negative conversion and digitisation, and there is more detail in my images (which I can vouch for because my tiffs have increased in size by 30%!). I now realise that a good light source is not something that should be overlooked if you’re serious about DIY scanning film negatives.