Green Channel Only & Pyro Negs?

**Carl Radford** · 23-Sep-2007, 02:39

Hi Folks

Just started scanning 5x4 negs on my epson 2450 using Vuescan and Make Gray From Green. Most of my negs are pyro - Pyrocat HD or PMK. I have noticed that these scan a lot darker than negs that I have that were developed in ID11. I am assuming that this is due to the pyro staining? If I do not use the green channel option the scans are lighter on pyro negs. Doesn't seem to affect the image when I adjust the b&w points in ps cs2. Don't want to get too far with scanning the negs and finding out I need to go back and start again

Any advice welcomed, cheers, Carl

**Ken Lee** · 23-Sep-2007, 04:38

The stain is brown - which is a red/orange. Scanning in green, is like looking through a green filter, which allows less red/orange to pass through. So it's not surprising that the resulting images would be darker-than-normal. If you were to gray from Red instead, you would see lighter-than-normal scans instead.

Do you find that your green-only images are sharper ? On my 4990, I haven't noticed much difference in sharpness with green-only.

**Carl Radford** · 23-Sep-2007, 04:51

Ken

I have spent sometime 'trying' to see a difference and am not sure I can. I also see that I get a very compressed tonal range so need to adjust b&w points considerably which concerns me. That said, the final image still looks ok. I might revert to scanning normally a ditch the other channels if I see a difference. Should I then out in 24 bit RGB or is there no difference to covert to RGB from a scanned 16 bit grey file?

**Ken Lee** · 23-Sep-2007, 09:19

Let's presume that the negatives are "normal" - they would print fairly easily on Number 2 paper, via contact print or cold-light-head enlarger.

It seems to me that a good scanner should have a broad dynamic range, so that the tonal extremes of "normal" negative should fall well within the range of the scanner. (Otherwise we would have no room to spare, as it were). If that is the case, then a normal negative, when scanned with all the default settings, should appear a bit soft.

I also presume that when you scan, you have set the white point and black point to 0. This tells VueScan not to clip any values - so you get the widest range of data from the negative. In addition, make sure not to include scan the blank film edge, since VueScan will be influenced by this low value, and you'll get junk.

So if the tonal range you get, needs to be stretched out a bit, that's probably a good sign. Given a 16-bit b&w scan, there are so many grey values available, that we can always adjust the b&w points (as you have been doing) and not lose much data in the process.

We can always increase contrast, but if your negatives are way too soft, then even a 16-bit file will suffer when you stretch the dynamic range back to normal. You'd be better off adjusting your development time to more closely match the native range of the scanner. When doing that, I would ignore the issue of Channels altogether: just scan all channels for now, until you get better "normalized".

I set VueScan to output 16-bit greyscale. In Photoshop, I convert to RGB mode, but I do that only after I have performed most of my corrections, and I am ready to apply a warm-toned color.

24-bit RGB (unless I am mistaken) allows only 8 bits per each of the RGB channels - the result being 24 bits. You're much better off performing all adjustments in 16-bit greyscale, to keep the smoothness of tonality that you worked so hard to capture with film in the first place. If you still prefer RGB, then let VueScan output in 48-bit RGB. This allows for 3 X 16 bits, IE 16-bit.

This example at InkjetArt.com (http://www.inkjetart.com/4990/48bit/page4.html) nicely illustrates the advantages of 16-bit workflow, using one of Ansel Adams more famous images, of the Grand Tetons.