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I've been using Luminance HDR for a while and I managed to understand the effect of most of the tonemapping algorithms, but there's still a thing that I don't fully understand. When I finish the importing procedure (selecting the pictures, aligning them and selecting the HDR parameters) this screen comes up.

The screen that comes up before selecting the tonemapping operator

From what I understand, it show the merged pictures without any tonemapping operator applied, just adding up the pixels. This hypothesis is supported by the fact that changing the "mapping" option or moving the blue slider doesn't affect the tonemapping result. I think this is just meant as a preview of what the actual HDR picture, or the tonemapped LDR one, will look like.

Is it correct or am I wrong?

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You are correct. The various operator options are different previews of the HDR - you can save them as tonemapped LDR images (*.tiff, *.jpg, *.png, *.bmp, *.ppm, .pbm, set from Tools > Preferences, under the 'Fast export' tab) using the panel on the left, or use the 'save as' button to save the image as an HDRi in one of 4 formats (.exr, *.tiff, *.hdr, *.pfs). The 'Update preview' button simply updates the tonemapped LDR image in the preview.

If you are creating an HDRi, you will probably just want to use the 'Save as...' button at the top, unless you are looking to make tonemapped LDR's.

  • This is clear, what I was uncertain about was the meaning of the tab which shows up before applying a tonemapping operator. I think it is the "real" HDR image, of which you can see only a portion (moving the blue slider above the picture) because the output device is not HDR. – gscaparrotti May 9 '18 at 9:15
  • Ok, I think I misunterstood your answer, we are basically saying the same thing. – gscaparrotti May 10 '18 at 6:56
  • yes, it basically tonemaps the preview image - you can see various tonemapped versions of the HDR on the right side, which affect the preview. As you say, the slider at the top also allows to see different parts of the dynamic range, since the monitor used cannot show so much dynamic range. – brandonmack May 31 '18 at 19:14
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Right. The image you see is a preview based on the values you select. You can set the size of the generated preview in the settings. In English, the UI is easier to understand as that button is labeled "Update preview" (in Italian, it's labeled "Processa", implying that the processing will happen when you click that button, but the final processing won't happen till you click the "Save as..." button, and select a file type (and other parameters) for the output.

  • I think we're talking about two different things. On the one hand, when I click on "update preview", the selected tonemapping operator (with the selected parameters) is applied to the given LDR pictures, and when it's done the corresponding preview is shown in a new tab: this is fine, it's what I'm expecting to happen. On the other hand, when I start creating a new HDR picture importing some new LDR pictures a new tab will show up (the one you can see opened in the original post), and I don't really understand what it is displaying: I haven't selected a operator yet, so what is it? – gscaparrotti Apr 1 '18 at 14:49
  • Is it the real HDR image before any tonemapping is applied? – gscaparrotti Apr 1 '18 at 15:14
  • At that point, I think you are seeing the default operator; whether that's the last one used or whatever. Personally, I tried the app to see what you were using, but I do not find this application at all intuitive. The Nik Collection's HDR Efex Pro (free, also) is much easier to get great results from, IMHO. And I also think Photomatix and/or Aurora HDR may be worth paying for, compared to Luminance HDR. I'm a proponent of open source, but that application is very slow, compared to others, and has pretty poor user experience. – Lowell Montgomery Apr 4 '18 at 6:06

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