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Najiajua

Histogram: Luminance is missing! Need help :(

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Hi community,

I got a problem with my histogram panel and already tried a reinstallation but it didn't help. My histogram only shows the values for rgb colours but not the luminance (the white curve is missing). I couldn't find any help for this problem, what can I do? (see attached file)

histogram.PNG

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It isn't missing. For some reason the developers decided to change the color of the luminance curve from white to a light shade of blue. If you look closely, you can see it in your screenshot.

There already have been requests to use white again but so far we are stuck with that odd choice.


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1 hour ago, R C-R said:

It isn't missing. For some reason the developers decided to change the color of the luminance curve from white to a light shade of blue. If you look closely, you can see it in your screenshot.

There already have been requests to use white again but so far we are stuck with that odd choice.

Omg that was too simple :) thank you so much, I always saw the light blue as an overlap of the blue and green colour and thought I just don't find the option to reactivate the real luminance curve. I also hope they will fix this, it was better before!

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12 minutes ago, Najiajua said:

I also hope they will fix this, it was better before!

Me too!


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1 hour ago, R C-R said:

Me too!

Me three!!


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5 hours ago, Dazzler said:

I think I'm going blind ... I don't see a light blue curve on that screenshot?

Luminance on histogram is showed in blue #20407C color aprox. on the other hand in levels adjustment is showed in white and part in blue #20407C.

 

 

Luminance_dif.jpg

Edited by Alareta
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3 minutes ago, Alareta said:

Luminance on histogram is showed in blue #20407C color aprox. on the other hand in levels adjustment is showed in white and part in blue #20407C.

 

Luminance_dif.jpg

I think your .jpg file did not upload properly. You might edit your post and try again :)


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5 hours ago, Dazzler said:

I think I'm going blind ... I don't see a light blue curve on that screenshot?

image.png.4ee134b8a3dddd619968f7ed4fca65f1.png

Here's another example: All Channels: image.png.e2ca28383caee1bc7c4af04a5b5474be.png

Just the Blue Channel: image.png.1b46c953a88941f85c55352166876bdb.png

The Luminance: image.png.0248427946fc2eb8e458dc91e3246ca4.png

Or, approximately what it would have been in 1.6:
image.png.e960739ecfe196cf4d67650d2c102417.png


-- Walt

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Surely that's just the overlapping area? Or is that what the luminance channel represents? Flicking through the three channels all I see is an overlap.

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I do think people spend too much time worrying about histograms. They can be really misleading at times .... consider a space scene where you are looking at a bunch stars ... it's going to be a massive peak all at one end of the histogram, and not a lot everywhere else - doesn't mean the photo is wrong or badly exposed - it's just the nature of the shot. If you're looking at a picture of something fairly small on a lawn then the green channel is going to dominate somewhat - doesn't mean the colour balance is out. Relying on a histogram is like putting your camera in full auto mode - a lot of the time it'll give you give you a decent shot but occasionally it'll completely mess up and prevent you from getting a shot that looks right.

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16 minutes ago, Dazzler said:

I do think people spend too much time worrying about histograms. They can be really misleading at times .... consider a space scene where you are looking at a bunch stars ... it's going to be a massive peak all at one end of the histogram, and not a lot everywhere else - doesn't mean the photo is wrong or badly exposed - it's just the nature of the shot. If you're looking at a picture of something fairly small on a lawn then the green channel is going to dominate somewhat - doesn't mean the colour balance is out. Relying on a histogram is like putting your camera in full auto mode - a lot of the time it'll give you give you a decent shot but occasionally it'll completely mess up and prevent you from getting a shot that looks right.

I agree with you, as controversial an opinion as that may be ;)

There appear to have been several threads about this lately—the main thing that needs to be said is that Affinity Photo's histogram does not represent luminance/luminosity. What you're seeing is the overlap/addition of the RGB channels. That's why it was changed from white, because users were mistaking it for luminosity.

If you want a better representation of luminosity, check out the Intensity Waveform on the Scope panel (View>Studio>Scope). That gives you an IRE readout and an abstract representation of your image, which is much more useful for seeing where the tones in your image are. You can also utilise an RGB Parade for a more accurate idea of where your colour channels may be clipping.


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12 minutes ago, James Ritson said:

There appear to have been several threads about this lately—the main thing that needs to be said is that Affinity Photo's histogram does not represent luminance/luminosity.

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

Quote

The Histogram panel shows the distribution of Red, Green, Blue, and Luminance values for the image, layer, or current selection.

So whatever the color, what does it actually show?


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33 minutes ago, R C-R said:

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

So whatever the color, what does it actually show?

...and there's the question that's actually kind of hard to answer.

It's showing you the amount of pixels present at any particular intensity value for that particular channel, where the intensity value ranges from 0 - 255 across the graph (presumeably normalised in some way to fit the graph height nicely).

Is it that useful? debateable. It can show you potential clipping issues (large spikes at ends of image) - but that's not necessarily always the case (space scene example), or lack of contrast issues  where most of the graph is present in the middle portion of the range (again could be you took a picture of some grey fabric that doesn't have a lot of contrast. It can show you colour casts where there appears to be a stronger presence of one channel against the others - only useful if you know there should be a neutral tone present - grey tones for example.

Having said that, in general (but not always) it's good to have a nice spread of values across the entire histogram, so that you have some presence in the light areas as well as the dark areas but not falling off the ends. It seems scientific, but it definitely needs to be used with commen sense and an appreciation of what any particular image SHOULD look like in it's representation. The space scene is probably the best example of how this can be mis-leading. Because there is a lot of dark in the picture you'll get a massive spike at the dark end, and a spike at the other end where the stars are represented.

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10 minutes ago, acapstick said:

This is incorrect in Photo Help at the moment. I've corrected this for 1.8.

Be that as it may, I just want to know what the light blue represents. From the technical note at https://www.cambridgeincolour.com/tutorials/histograms2.htm, a luminosity histogram "refers to the perceived brightness of that object by a human observer."

As I understand it, it is a weighted average of RGB values, with a strong emphasis on green (59% of the total) because the green part of the visible spectrum is what our eyes are most sensitive to, whereas a luminance histogram is unweighted.

So is it either one of these things or something else?


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1 hour ago, James Ritson said:

What you're seeing is the overlap/addition of the RGB channels.

This raises three questions for me;
1: What dose this actually mean.
2: Why do I need a graphical representation of point 1 above.
3: How do I use this information in a meaningful way.

Like R C-R I still find myself a little in the dark about this.


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50 minutes ago, Dazzler said:

It's showing you the amount of pixels present at any particular intensity value for that particular channel, where the intensity value ranges from 0 - 255 across the graph (presumeably normalised in some way to fit the graph height nicely).

I think it would be more accurate to say that it shows brightness rather than intensity, but either way the switch to the light blue color makes no sense to me. If anything, it suggests there is some connection to blue levels, while white does not, so why change it?

Also, why is the background in the dark UI mode black? That just makes it harder than it should be to see the blue channel info. 


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2 minutes ago, R C-R said:

I think it would be more accurate to say that it shows brightness rather than intensity, but either way the switch to the light blue color makes no sense to me. If anything, it suggests there is some connection to blue levels, while white does not, so why change it?

Also, why is the background in the dark UI mode black? That just makes it harder than it should be to see the blue channel info. 

As pointed out by James Ritson, there is no light blue,  it's merely an overlap of the three channels that is producing that colour - the old method of showing white where they overlapped has been removed. As far as I can see the overlap means nothing at all.

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1 minute ago, Dazzler said:

As pointed out by James Ritson, there is no light blue,  it's merely an overlap of the three channels that is producing that colour - the old method of showing white where they overlapped has been removed. As far as I can see the overlap means nothing at all.

There very clearly is a light blue -- just look at the screenshot in the reply above by @walt.farrell & what he circled in red. If it is supposed to be "the overlap/addition of the RGB channels" then why does it dip so low toward the right where red & green peak?

We need a clear & simple explanation of why it is there, whatever it is, & also if it does not represent luminosity (or luminance) why the histogram does not include one or the other.


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Here's some things to try if you are wondering quite what the histogram shows.

1. Fill the entire screen with a flat colour (make a rectangle and choose a fill colour). Now look at the histogram. You'll see three peaks at the RGB values for that colour. Now adjust the contrast quite a bit - what happens to the colour and the histogram?
2. Fill the entire screen with a black to white gradient in the same way - now look at the histogram. Should be a fairly even line across the top of the histogram.
3. Place a colour image - then convert to black and white and compare the histograms. Now, on the black and white picture up the contrast to max.  You'll probably notice gaps appearing in the histogram where the values are getting pulling apart from each other. What happens when you do a threshold adjustment? Now flatten the image and gaussian blur the result. How does that look?
4. Take a photo, look at the histogram and then do a colour balance whilst looking at the histogram and see how it affects it. This may be more apparent if you do it on a black and white image.
5. Take a few really nicely shot stock photos and place in and look at the histogram. Do the histograms appear as you expected or not?


I'm not saying there's no point in having a histogram, but you need to know what it's showing you before making decisions based on that info. It's literally counting pixels that have that Red or green or blue value depending on which channel you are looking at and at what point along the graph. Simply doing levels or contrast to pull the values to just inside both ends of the histogram is not always the right thing to do. It's generally a good idea to do this but context is very important. Not all photos should have a white or black point, most should but not all.

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3 minutes ago, R C-R said:

There very clearly is a light blue -- just look at the screenshot in the reply above by @walt.farrell & what he circled in red. If it is supposed to be "the overlap/addition of the RGB channels" then why does it dip so low toward the right where red & green peak?

We need a clear & simple explanation of why it is there, whatever it is, & also if it does not represent luminosity (or luminance) why the histogram does not include one or the other.

No there isn't a light blue. It is simply the overlay of the colour channels. The dip you are talking about is clearly the blue channel. Just open Photo and grab a photo and flip between the three colour channels in the histogram and you'll see that it is simply a transparency on the three channels and where they overlap you get the combined colour. Nothing more than that. Luminosity is roughly going to be the chart ranging from left to right, not upwards in the histogram as you might expect. ie. A full white image would simply be a spike at the very right hand side of the histogram, that would be full luminosity across the whole image - not a line going across the top of the histogram as you might be expecting.

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8 minutes ago, Dazzler said:

I'm not saying there's no point in having a histogram, but you need to know what it's showing you before making decisions based on that info.

Exactly my point! As things stand now, we do not know what it is showing, or for that matter why the histogram lacks a luminosity (or luminance) curve.


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6 minutes ago, Dazzler said:

No there isn't a light blue. It is simply the overlay of the colour channels.

Look carefully at that screenshot. Note that there is a bright edge at the top of what is circled in red, just like the bright edges for the red, green, & blue channels. If it is nothing more than the overlap, why is it there?


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