How to do image slices in DT 5.4.0?

Software darktable
1

DT 5.4.0 on debian

Is there a way in DT to create 1 single image with 5 exposures/slices, from -2EV to +2EV? So I can send it to the printer then I can adjust the whole serie when I get the enlargements from the printer.

Right now, I do 5 different exposures with 5 exported images, then I use magick to cut them and then I use slice 1: -2ev, slice 2: -1ev, slice 3: 0ev… to reassemble them with magick. But that’s a lot of work.

Could I do that in DT?

Thanks

2

wouldn’t masks in DT work for this?
Here I have used masks to create four different exposures in 0.5 EV steps.

image
image1504×984 638 KB

7 Likes
3

That would be fantastic!

How do you do the mask?

Thanks

4

Here is the file and if you download my xmp file as well you will see how it is masked.
For each instance of exposure I have used the path option for a drawn mask. I have held the ctrl button down (windows) while placing the four nodes for the path. This creates straight lines for the mask selection. You will need to reduce the feathering as well after drawing the mask. Shift + scroll will adjust feathering on Windows.

R7__1128.CR3.xmp (19.0 KB)
R7__1128.CR3 (39.1 MB)

5 Likes
5

Thank you very much.

I downloaded your photo + the xmp and will study it this weekend

Thanks

6

Personally I don’t think DT is the best tool for this but I understand not wanting to have yet another tool in the process.

This seems like something that could be scripted pretty easily using imagemagick or similar tools.

7

What is the purpose of it? Is it only to compare? To print?

8

Now I understand. :+1:

Thanks

9

As explained in my original post. I’m currently using imagemagick v7/magick v1 to do it. I have my script but it’s not fully automatic. So I wandering if I could achieve the same result in DT to save me time.

10

Printing vs screen is not accurate, even when the screen is calibrated.

  1. That way, I can evaluate and modify the processing from the print.
  2. Sometimes it’s for the screen. Different exposures are just as valid but give a different feeling.
11

Are you printing at home or using a printing service? If using a printing service is it a professional or consumer grade service? If at home what printer?

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Ok that was what I suspected. A little bit like when printing in a darkroom

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It’s for 2 purposes:

  1. Me deciding what I ‘really’ want from this image.
  2. For printing.

I have 2 services for printing:

  • a very cheap: walmart (they are pretty good if you follow their requirements and up to 5x7)
  • a very good one, but they are expensive that I use for large sizes: ‘the lab’ in vancouver, canada.
14

My only suggestions since you are out sourcing your printing is to at Walmart check exposure and color on their kiosk and see if their prints match their kiosks. If your lucky it will and then you can do final tweaks on their kiosk.

With the pro lab talk to them about the issue and follow their advice. They may provide a print profile.

I print at home and I have to apply corrections for my printer to make it close to the computer screen. Luckily these corrections hold true for all the prints on that paper type so it is not an ongoing problem.

Also keep in mind a computer screen is transmitted red, green and blue pixels of transmitted light and a print is a reflection off yellow, magenta, cyan and black inks. They will never perfectly match under the best circumstances. They can only be close to each other.

You can get more control if you can justify buying your own home printer.