Waveform histogram

afre · September 20, 2019, 4:08pm

This comes up once in a while and I usually add the comment or two that I would absolutely love more types of visualization of the data. I have also seen some inventive variations of the standard waveforms and vectorscopes.

@dafrasaga What is your particular use case for a waveform? What kind are you looking for?

dafrasaga · September 20, 2019, 4:12pm

Hi, I saw it in a tutorial where It is useful for ETTR exposition, but I do not understand more

afre · September 20, 2019, 5:20pm

ETTR is something you figure out while taking the photo.

Entropy512 · September 20, 2019, 6:12pm

The main benefit of the waveform display is that it not only lets you see that you’re clipping a channel in the histogram, but to give you an idea of WHERE in your image (at least in the horizontal plane) you are clipping.

An alternative to this is a mix of histogram and “zebras” or other methods of over/underexposure highlighting that change the color of a pixel if it is brighter or darker than a given threshold.

heckflosse · September 20, 2019, 6:52pm

@hanatos showed me the Waveform histogram at lgm 2019, and it’s really cool. Maybe we can steal the code

afre · September 20, 2019, 7:35pm

It is a steal for sure.

heckflosse · September 20, 2019, 7:37pm

Well, that balances over the time

darix · September 20, 2019, 7:50pm

afre · September 20, 2019, 8:02pm

Representing all Canadians.

dafrasaga · September 21, 2019, 4:27am

Ok, I know it… in fact it was obscure because waveform histogram in post production would done useful for ETTR.

dafrasaga · September 21, 2019, 4:34am

In RT , when I want to know where is clipping I use, as you, the clipping indicator and for what channel is clipped the preview channel button at the top of the preview window…therefore… what is the utility of the waveform histogram for that… ?

Thanatomanic · September 21, 2019, 4:54am

For reference: Add more scopes · Issue #4763 · Beep6581/RawTherapee · GitHub

dafrasaga · September 21, 2019, 5:08am

Thanks for the information

hanatos · September 23, 2019, 7:19am

i doubt you need to steal these two lines of code. probably faster to type your own version than to copy/paste + fixup… :

github.com

darktable-org/darktable/blob/master/src/develop/pixelpipe_hb.c#L995


      
          
            const dt_iop_order_iccprofile_info_t *const profile =
              dt_ioppr_get_pipe_current_profile_info(module, piece->pipe);
          
            dt_color_picker_helper(dsc, pixel, &roi_copy, box,
                                   darktable.lib->proxy.colorpicker.primary_sample->denoise,
                                   pick, image_cst,
                                   dt_iop_color_picker_get_active_cst(module), profile);
          
            for_four_channels(k)
            {
              picked_color_min[k] = pick[DT_PICK_MIN][k];
              picked_color_max[k] = pick[DT_PICK_MAX][k];
              picked_color[k] = pick[DT_PICK_MEAN][k];
            }
          
          error:
            dt_free_align(tmpbuf);
          }
          #endif

github.com

darktable-org/darktable/blob/master/src/libs/histogram.c

/*
    This file is part of darktable,
    Copyright (C) 2011-2023 darktable developers.

    darktable is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    darktable is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <stdint.h>

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dafrasaga · October 24, 2020, 5:09am

WOW!! waveform is in dev @Lawrence37 Thanks a lot !!

Sunhillow · October 25, 2020, 3:46pm

Now my task will be to understand what it indicates

heckflosse · October 25, 2020, 3:53pm

The horizontal axis in the waveform histogram corresponds to the horiziontal axis of your image. Means you can see where for example highlights are clipped

Sunhillow · October 25, 2020, 3:58pm

Thanks! Now as you say it … I also had a look at the video linked a bit above. So the white bar on top indicates “all channels clipped”.
And big thanks for implementing all kind of useful tools!

heckflosse · October 25, 2020, 4:00pm

Don’t thank me, thank @Lawrence37, who implemented waveform and vectorscope for RT and he’s the one who can give you better answers for this than me.

mbs · October 25, 2020, 4:19pm

This is a good explanation: How to Use and Read the Four Primary Video Scopes

I just compiled the latest dev, and the new scopes seem to be working great. These are very useful tools, thanks @Lawrence37!