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Display luminosity in Histogram or Levels


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Long-time user of Serif products, chiefly PagePlus and PhotoPlus, but also WebPlus, CraftArtistProfessional and DrawPlus.  Delighted to be using Affinity Designer, Photo, and now Publisher, version 1 and now version 2.

iPad Pro (12.9") (iOS 17.4) running Affinity Photo and Designer version 1 and all three version 2 apps.

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4 hours ago, henryg said:

there (still) no way for the live histogram or levels adjustment to display luminosity?

What does the histogram display to you if not luminosity?

I'd rather say the histogram always displays luminosity, considering that an image, like any color (> hue), becomes visible only with light (> luminosity). So, in the histogram luminosity is displayed as graph horizontally increasing (left: 0 / right: 100%) and below additionally numerically (0-255 / 0-100) if the cursor is hovering over the graph.

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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15 hours ago, thomaso said:

What does the histogram display to you if not luminosity?

I'd rather say the histogram always displays luminosity, considering that an image, like any color (> hue), becomes visible only with light (> luminosity). So, in the histogram luminosity is displayed as graph horizontally increasing (left: 0 / right: 100%) and below additionally numerically (0-255 / 0-100) if the cursor is hovering over the graph.

Pls excuse my ignorance, but I don't want to see the individual colour components, just one "line", as shown in the curves adjustment.

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26 minutes ago, henryg said:

Pls excuse my ignorance, but I don't want to see the individual colour components, just one "line", as shown in the curves adjustment.

If you look at the Histogram in the Curves adjustment you will see that it matches the White histogram in the Levels adjustment (just ignore the other colours)

PS It may have been better for the Levels adjustment to have renamed "Master" to "All channels" as that is what it is displaying

same.jpg

To save time I am currently using an automated AI to reply to some posts on this forum. If any of "my" posts are wrong or appear to be total b*ll*cks they are the ones generated by the AI. If correct they were probably mine. I apologise for any mistakes made by my AI - I'm sure it will improve with time.

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On 11/11/2021 at 2:51 PM, henryg said:

Curves adjustment does, or appears to do to me, but that is not where I want it.

Curves and Levels Adjustments can show luminosity, and you can have multiple so that one applies an effect while another on top of it just measures it, mimicking a live histogram similar as in Photoshop, but the update mechanism is odd and clunky (it seems to require reactivating of the measured image/pixel layers), and histograms related to Adjustments cannot be kept in view similarly as the actual Histogram panel:

luminosity_aphoto.thumb.jpg.5f0766f5a5489455b63eb2ee5e2d820c.jpg

luminosity_ps.thumb.jpg.b2da7f7f6daf0b9e98a806653ad90a41.jpg

 

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@henryg, are you in Windows or macOS?

3 hours ago, carl123 said:

If you look at the Histogram in the Curves adjustment you will see that it matches the White histogram in the Levels adjustment (just ignore the other colours)

Interesting, in macOS the histogram in the Curves Adjustment displays colors similar to the Histogram Panel  in macOS: with a blueish gray as summary* common area of r+g+b (while the UI in the Level Adjustment displays it like in Windows, white as their summary* common area). In particular in the Histogram Panel the blueish summary can mislead.

721814967_histogramsummaryvsblue1.jpg.a3a16a070bac339d12e6c8fffbc20f2f.jpg

Although the summary histogram seems to be displayed more clear with the example image below it doesn't seem to show a summary but just 3 overlapping channels only. Also, it may confuse for single channel view: these occur scaled, – with the goal to fill their min/max area?

536836358_histogramsummaryvsblue2.jpg.1682aba84421979a93256f19eb894d16.jpg  1653091233_histogramsummaryvsgreen.jpg.5df2cbab2e095413844c2723ece2f707.jpg

This makes me wonder how you get the total (r+g+b) curve displayed in Windows?

Here the UI is indeed confusing, apparently the curves of each channel are semi-transparently overlaid, with blue (rgb) or yellow (cmyk) as front most color, so the total ink area appears blue or yellow – different to the levels adjustment's graph with clear white or to the colors adjustment with gray.

972390811_histogramgradientrgb.jpg.c08dae192f2002dc1f4e7fc19607f209.jpg  1292093036_histogramgradientcmyk.jpg.0bec8ad3ae450c9bddaa0082b4fb737c.jpg


This could mean the OP actually is missing in the Histogram Panel a clear distinction between color channels & their summary* common area. Additionally an option to display the entire graph with 1 color only may be helpful, too.

I fully agree with this need. Does one know whether it got posted yet posted as a request?


* EDIT: Actually none of the histograms displays a "summary" of colors as I posted erroneously. In fact this color in the graph illustrates the area which all channels have in common. It is simply the overlapping area of the channel diagrams as the Help says:

1067512924_histogramoverlappingcommonarea.jpg.9e67a8f90bca16e3b3bc4057c5a1a211.jpg

Edited by thomaso
Addition because of misused/misleading term "summary"

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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6 minutes ago, Lagarto said:

Curves and Levels Adjustments can show luminosity,

OP: "that is not where I want it."

I suppose it is requested for the Histogram Panel, not for adjustment histograms which maybe rather mentioned as samples of possibilities existing in Affinity.

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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On 11/11/2021 at 6:51 AM, henryg said:

I'm returning to using APhoto after many many months, but is there (still) no way for the live histogram or levels adjustment to display luminosity? Curves adjustment does, or appears to do to me, but that is not where I want it.

 

Have you tried using the Scope Panel? It has a Intensity Wave Form.

https://affinity.help/photo/en-US.lproj/pages/Panels/scopePanel.html

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On 11/12/2021 at 10:45 AM, carl123 said:

If you look at the Histogram in the Curves adjustment you will see that it matches the White histogram in the Levels adjustment (just ignore the other colours)

PS It may have been better for the Levels adjustment to have renamed "Master" to "All channels" as that is what it is displaying

same.jpg

That is a big help, thank you. The white levels histogram seems to be a close if not identical match for the the light-blue one  in the live histogram panel once I adjust the display scaling - see below, in which case it solves my problem, albeit that it is not the most clear representation.

image.png.e16349295a90a4871024c0410729f674.png

 

 

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On 11/12/2021 at 1:17 PM, Lagarto said:

Curves and Levels Adjustments can show luminosity, and you can have multiple so that one applies an effect while another on top of it just measures it, mimicking a live histogram similar as in Photoshop, but the update mechanism is odd and clunky (it seems to require reactivating of the measured image/pixel layers), and histograms related to Adjustments cannot be kept in view similarly as the actual Histogram panel:

LAB Lightness looks to be the same to my eye as Curves Grey Master, as opposed to Curves RGB Master. So is Curves Grey the same as Luminosity? And so what does the light-blue scale in the Live Histogram represent?

 

Yet according to thomaso's quote above

histogram overlapping common area .jpg

the light-blue values do not reflect luminosity, which if correct means I have to assume the white levels values similarly do not reflect luminosity. So I get even more confused, I'm afraid.

I am finding my ignorance rather embarrassing.

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On 11/12/2021 at 11:45 AM, carl123 said:

If you look at the Histogram in the Curves adjustment you will see that it matches the White histogram in the Levels adjustment (just ignore the other colours)

1 hour ago, henryg said:

the light-blue values do not reflect luminosity, which if correct means I have to assume the white levels values similarly do not reflect luminosity. So I get even more confused, I'm afraid.

Additionally to this irritation the various graphs got different design in Windows vs. Mac concerning a.) the common, overlapping area and b.) the illustrated channels: So, in @carl123's screenshot the Curves adjustment histogram is 1 gray area only but it is NOT the luminosity but appears to show instead the common, overlapping parts of all channels – which is of course confusing. Accordingly "just ignore the other colours" in any of the histograms doesn't solve the problem. 

Different to Windows in macOS the Curves histogram displays all channels (in color) AND does not show the overlapping area with a neutral color (white or gray) but as a semitransparent color of the front most channel in the histogram – which makes this UI on a Mac even more confusing. Unfortunately the Help doesn't show a screenshot of the Curves adjustment or Level adjustment dialog windows which makes it hard to check if the histogram design seen by users locally does look like the intended, coded "by design" design. However, the Help's interface overview shows on Mac the Histogram Panel with this vaguely blueish tint for the overlapping area which may indicate at least in this panel the appearance is in purpose.

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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On 11/13/2021 at 3:02 PM, henryg said:

So is Curves Grey the same as Luminosity?

I am not an expert but I think that it is (basically same as intensity of light), and it seems a weighted conversion, similar as when creating an actual grayscale conversion and saving the result as grayscale file (e.g. TIFF), and identical to weighted conversion done by Photoshop, where the green has the biggest weight factor, then red, and blue the smallest (according to sensitivity of human eye to different wavelengths/colors of light). The Lab color space has the other two parts colors represented by opposing axes of red and green, and blue and yellow.

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In the adjustment histograms of Affinity the Grey (Intensity) and LAB (Lightness) menu options are not exactly the same because of the weighted conversion mentioned by Lagarto, which will cause a slightly different diagram depending on the colors in the specific image. If the grey diagram view would not automatically do a color conversion* then grey could be the same as luminosity.
* if you choose grey for the histogram and close the window the image will remain displayed grey.

351827405_histogram1-3.jpg.fc7694932e595a0cef2386f2253df308.jpg

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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thomaso

if you choose grey for the histogram and close the window the image will remain displayed grey.

Yes, I realised this when I was playing around with the various options.

LAB lightness may be the way to go, BUT then holding down the alt key while using the Level's sliders to show blown-out areas doesn't seem to work, which is a bit of a pain.

Perhaps for me, using the white area in the Levels display may be an acceptable compromise in most cases. If not on the odd photo, then I can always use LAB Lightness or indeed Curves; probably the latter.

And I should have said that I am using Windows, but I think that sort of became clear. Sorry, nevertheless.

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