Can I easily and automatically fix contrast and color on a 35mm scan that contains sprocket holes?

fabulousrice · Apr 4, 2024

I often prefer to scan film including the sprocket holes, especially when the image bleeds over the perforations a little bit, as in this example:

The raw results from the scanner are usually very bland. Whenever I scan without perforations, I fix this by using Auto Tone/Contrast/Color in Photoshop, which is fast and gives acceptable results.

But when I scan with the perforations, using these commands does not work, probably because of the perforations throwing off the way the program perceives the image.

Inside the dotted selection, the correction provides a proper result:

However when applied to the whole scan (including perfs), the Auto commands do not produce a good result:

I wish I could "sample" part of the image that I want to fix automatically, and then apply this to the rest of the image.

I prefer not to create presets or actions but would rather use an auto feature, since I use different film stocks all the time.

I am sure that if I selected the exposed parts and deselected the perforations and edge markings, the Auto commands would work a bit better, but I am trying to find a quick way to balance these scans and restore the dullness that the scan produced. I'm open to try a new app if one does what I'm looking for.

How can I balance these scans out?

koraks · Apr 4, 2024

Automatically: no, I don't think so. Part of the reason is that there's no way a computer can guess your artistic intent.

I'd scan the entire roll with the same settings (i.e. no color adjustments done by scanner & scanning software) and then work out a curve (manually/by eye) that approximates what you want, and apply that to all frames. Then finish off by manually finetuning individual frames to taste.

For instance, an overall curve adjustment could look something like this:

Here, I assumed that you would want the film base to be barely visible, and I approximated the colors you seem to prefer for the middle frame. Such assumptions about your preferences are precisely why I think an automatic adjustment is likely to always fail; all it can do is balance everything out to an average middle grey.

PS: the auto-adjustment may not be as bad as you think, but because it's thrown off by the large empty space, you could try and shifting the shadow point a bit to press down the film base deeper into the shadows, like so:

fabulousrice · Apr 4, 2024

koraks said:
Automatically: no, I don't think so. Part of the reason is that there's no way a computer can guess your artistic intent.

I'd scan the entire roll with the same settings (i.e. no color adjustments done by scanner & scanning software) and then work out a curve (manually/by eye) that approximates what you want, and apply that to all frames. Then finish off by manually finetuning individual frames to taste.

For instance, an overall curve adjustment could look something like this:
View attachment 367330
Here, I assumed that you would want the film base to be barely visible, and I approximated the colors you seem to prefer for the middle frame. Such assumptions about your preferences are precisely why I think an automatic adjustment is likely to always fail; all it can do is balance everything out to an average middle grey.

PS: the auto-adjustment may not be as bad as you think, but because it's thrown off by the large empty space, you could try and shifting the shadow point a bit to press down the film base deeper into the shadows, like so:
View attachment 367331

Thank you so much for your quick and clever reply!
I am wondering if a curve would work as well as using an "Auto" feature for each independent image - since some images will be underexposed or overexposed, some would be cooler or warmer...
Usually when I try to fix the colors myself I end up not thinking it looks as good as the auto results. My best results are actually through the Levels window. I will try your ideas!

koraks · Apr 4, 2024

Well, I think personal taste plays a role here as well, and I have to admit I'm not a fan of automatic adjustments. The advantage of those is that indeed, they do adjust to the specific nature of each individual image. However, they also tend to work as a black box, which means it either works, or it doesn't, and you're never quite sure how to manipulate it to do what you want.

The full-manual approach, on the other hand, is infinitely flexible, but therefore also more laborious.

I try to strike a middle ground by working manually, but applying a (manual) base adjustment to all images on the same roll of film, and then individually adjusting frames if required. For instance, in the example of the 3 images above, I would raise contrast for the left frame (the dark one) and adjust color balance for the right frame (the one shot under fluorescent lights). But I'd start with the same base adjustment for all, and choose an adjustment that won't cut off any important detail that I might for the individual adjustments.

It helps if you scan and work in 16 bit color depth, especially because you're layering several adjustments on top of each other and in 8 bit mode, this easily creates problems with posterization.

loccdor · Apr 4, 2024

I have had similar thoughts as the original poster. Not about sprocket holes in particular, but I noticed that the auto-adjustment for color negative film would often look bad and leave casts for certain types of images. Images that did not include sky or a bright white point in particular, and images with a lot of the same color.

There is definitely a way to write an image processing program that performs auto-adjustments on a selection, saves the curves created by this operation, then applies it to the full image. And it seems like a common enough problem that a solution has to have been written. But I haven't seen it personally. I have experience writing programs with image processing libraries and might have given it a shot sometime - if I was satisfied with the auto results to begin with. But this is the sort of thing that could be coded by a programmer in a few days/weeks. If I was going to try, I'd use the CImg library. I believe most of these adjustments are arrived at using min/max values and averages, I wouldn't expect it to have much complex math or operations. Making a curved line function out of points seems like it would be the most mathematical part.

In the end I found I did have to spend a lot of time with manual adjustment on color negative film to get satisfactory results. I look back on my color negs from when I was first starting with film and they are full of color casts that I was barely noticing at the time.

Now it's not uncommon for me to spend 10-20 minutes adjusting a difficult color negative image that I care about to get it just right. Auto is good enough for quick previewing sometimes, but for a final polished image it's better to spend the time. Since eyes adjust, when working on a picture it can be good to take a break for a bit, walk a way and forget about it, then come back. Then see if your settings still look good.

I start with setting the min and max of each color channel to the min/max values recorded. In the case of sprocket holes, you'd want to start your min somewhere between the black of the sprocket hole and the darkest value on the film. Then pull the channel curve lines up or down starting at the center until the image achieves the best balance to your eye. Note that some images actually look better cooler or warmer than reality.

brbo · Apr 4, 2024

In PS:

- make a selection that doesn't include sprockets
- add new curves adjustment layer
- hold 'Alt' and click 'Auto'
- select 'Find Dark & Light Colors'
- right click on mask and select 'Disable Layer Mask'

Now you have 'Auto Color' applied to entire image without sprockets influencing the analysis of AC algorithm.

runswithsizzers · Apr 4, 2024

Some scanning software -- for example, Vuescan -- has a setting that allows some percentage around the edges of the crop rectangle to be ignored when calculating exposure /contrast. With Vuescan, it is called Crop Buffer, and the user can specify a percentage to be ignored. Negative Lab Pro also has a Border Buffer setting where you can specify some percentage at the edge of the frame to be ignored.

fabulousrice · Apr 4, 2024

loccdor said:
I have had similar thoughts as the original poster. Not about sprocket holes in particular, but I noticed that the auto-adjustment for color negative film would often look bad and leave casts for certain types of images. Images that did not include sky or a bright white point in particular, and images with a lot of the same color.

There is definitely a way to write an image processing program that performs auto-adjustments on a selection, saves the curves created by this operation, then applies it to the full image. And it seems like a common enough problem that a solution has to have been written. But I haven't seen it personally. I have experience writing programs with image processing libraries and might have given it a shot sometime - if I was satisfied with the auto results to begin with. But this is the sort of thing that could be coded by a programmer in a few days/weeks. If I was going to try, I'd use the CImg library. I believe most of these adjustments are arrived at using min/max values and averages, I wouldn't expect it to have much complex math or operations. Making a curved line function out of points seems like it would be the most mathematical part.

In the end I found I did have to spend a lot of time with manual adjustment on color negative film to get satisfactory results. I look back on my color negs from when I was first starting with film and they are full of color casts that I was barely noticing at the time.

Now it's not uncommon for me to spend 10-20 minutes adjusting a difficult color negative image that I care about to get it just right. Auto is good enough for quick previewing sometimes, but for a final polished image it's better to spend the time. Since eyes adjust, when working on a picture it can be good to take a break for a bit, walk a way and forget about it, then come back. Then see if your settings still look good.

I start with setting the min and max of each color channel to the min/max values recorded. In the case of sprocket holes, you'd want to start your min somewhere between the black of the sprocket hole and the darkest value on the film. Then pull the channel curve lines up or down starting at the center until the image achieves the best balance to your eye. Note that some images actually look better cooler or warmer than reality.

Thanks for this amazing answer.
Yes I wish the Auto commands just wrote what the steps are into the History pane of PS...
How do you achieve "I start with setting the min and max of each color channel to the min/max values recorded."? How do you record them?

fabulousrice · Apr 4, 2024

brbo said:
In PS:

- make a selection that doesn't include sprockets
- add new curves adjustment layer
- hold 'Alt' and click 'Auto'
- select 'Find Dark & Light Colors'
- right click on mask and select 'Disable Layer Mask'

Now you have 'Auto Color' applied to entire image without sprockets influencing the analysis of AC algorithm.

I just tried and it didn't seem to change anything?

(http://imgur.com/a/DnWTsy4)

fabulousrice · Apr 4, 2024

runswithsizzers said:
Some scanning software -- for example, Vuescan -- has a setting that allows some percentage around the edges of the crop rectangle to be ignored when calculating exposure /contrast. With Vuescan, it is called Crop Buffer, and the user can specify a percentage to be ignored. Negative Lab Pro also has a Border Buffer setting where you can specify some percentage at the edge of the frame to be ignored.

Ah, if only VueScan had a pleasant user experience associated to it - and if its licensing system let users buy once and install across devices - what a wonderful world we would live in! I've given them a lot of money and I don't see it go into bettering their program

Patrick Robert James · Apr 4, 2024

Vuescan has gone forwards and backwards recently. They stopped supporting “crop all“ on my Nikon so now when I want to scan an entire roll, unless I use an old computer and an old version, I get bloated files. I inquired about it and only got the response “it doesn’t work like that anymore”. Disappointing….

A super fast way to set the black level is to use the black eyedropper in the curves/levels dialog. You could do it after you set the highlight with “find dark/light”. Then use the shadow eyedropper and click in the rebate. It will set it to black and voila. Doing so will also help color balance the image. If you double click on the eyedropper you can set it to any value you want. The same goes for the highlight eyedropper.

brbo · Apr 5, 2024

fabulousrice said:
I just tried and it didn't seem to change anything?

Just draw a rectangle with select tool around the image (not including the sprockets and rebate of the negative.

The way you do the selection will include the entire rebate and also possibly some of the sprockets or parts that have much less density than even the rebate which will throw off the Auto Color.

fabulousrice · Apr 5, 2024

brbo said:
Just draw a rectangle with select tool around the image (not including the sprockets and rebate of the negative.

The way you do the selection will include the entire rebate and also possibly some of the sprockets or parts that have much less density than even the rebate which will throw off the Auto Color.

Whoa thank you so much! Although I get better results when I select "Enhance per channel contrast" than with find light & dark". This trick just changed my life!

Can I easily and automatically fix contrast and color on a 35mm scan that contains sprocket holes?

fabulousrice

How can I balance these scans out?

koraks

Moderator

fabulousrice

koraks

Moderator

loccdor

brbo

runswithsizzers

fabulousrice

fabulousrice

fabulousrice

Patrick Robert James

brbo

fabulousrice

Can I easily and automatically fix contrast and color on a 35mm scan that contains sprocket holes?

How can I balance these scans out?​

Moderator

Moderator

Privacy & Transparency

Privacy & Transparency

How can I balance these scans out?