Jump to content
Najiajua

Histogram: Luminance is missing! Need help :(

Recommended Posts

3 minutes ago, R C-R said:

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?

I see the edges, and yes the combined colour makes a light blueish colour, but if you did as I said and flipped through the channels you'd see there is no fourth value being presented there. The reason for the transparency is so you can see all three channels against each other.

The histogram is something I've had great difficulty with when teaching people how to use Photoshop. It's not that I don't understand it, it's that it doesn't actually make a lot of sense unless you know what exactly you're looking at. People see is as some sort of brightness curve, but it's not that at all. It's a screen estate measurement. It's really hard to explain becuase really there's not a lot of point in that information apart from to tell you if you have no values happening at the ends which could suggest a lack of contrast in your picture, and as I said previously, not all pictures need a white and a black point. It's not a case of the ends should definitely be at the bottom either. As I said read the y-axis as 'amount of screen taken up with this value' and you see how weird a measurement is actually is. It's easy to calculate from a programming point of view which is why it gets added.

Share this post


Link to post
Share on other sites
10 minutes ago, Dazzler said:

I see the edges, and yes the combined colour makes a light blueish colour, but if you did as I said and flipped through the channels you'd see there is no fourth value being presented there.

Obviously, there is only one channel shown if you set the display to show only one channel (which BTW could be any of 4 channels for a CMYK document) so I don't understand why you think that is significant. Regardless, it does not explain the bright edge on the light blue part in the center of the screenshot histogram -- if the light blue is just a transparency blending effect of overlaying the color channels, there is nothing I can see that would explain that. Do you?

I do understand that histograms have to be interpreted correctly to be useful, but I do not agree that there is not much point to them, particularly when editing photos or original artwork, for example when deliberately trying to create an artificial or painterly effect or comparing the color distribution of different layers or selections -- it is not always all about what is happening at the ends of the channel curves.

Besides, as the Cambridge tutorial mentions, there are times when a luminosity histogram can be useful, so why omit that from the Affinity ones?

Share this post


Link to post
Share on other sites
29 minutes ago, R C-R said:

Obviously, there is only one channel shown if you set the display to show only one channel (which BTW could be any of 4 channels for a CMYK document) so I don't understand why you think that is significant. Regardless, it does not explain the bright edge on the light blue part in the center of the screenshot histogram -- if the light blue is just a transparency blending effect of overlaying the color channels, there is nothing I can see that would explain that. Do you? 

All I was trying to say by flipping between the channels is you can clearly see the way the edges lie for each channel, then when you compare to the combined 'all channels' view you can match each to it's repsective colour chart in the combined view, then you'll see there is no imaginary fourth area, it's just where they overlap. If you don't believe me take a screen grab of each individual colour, then composite them together with some transparency and you'll get the combined view - stacking them red at back, green in middle, blue on top.

I agree a luminance value would have some use, I'm not saying it wouldn't, and probably more so than the individual channels, but it's definitely not the same as the white area that looks like it used to highlight where all three regions were combined which is somewhat misleading to say the least. I can see why they removed it.

Share this post


Link to post
Share on other sites

Hum… So can someone give an actual real world example where seeing this RGB overlap in  AP’s Histogram is useful ?
Right now it seams to me, that in terms of usefulness while editing and image, that blue overlay of RGB overlap might as well be telling me how much rain fell today.

Share this post


Link to post
Share on other sites
38 minutes ago, Dazzler said:

All I was trying to say by flipping between the channels is you can clearly see the way the edges lie for each channel, then when you compare to the combined 'all channels' view you can match each to it's repsective colour chart in the combined view, then you'll see there is no imaginary fourth area, it's just where they overlap.

Except that you often can't do that because each view is normalized separately. Besides, even when that works it does not explain the bright edge in the All Channels view.

As for the white area, compare the Histogram panel display to the one in the Levels Adjustment window, which still has a white area. Try changing levels there & then compare it to the histogram. Something still isn't right because they don't match up, whether comparing the Master vs. All Channels display or to any of the single channel views.

Share this post


Link to post
Share on other sites
14 minutes ago, R C-R said:

Except that you often can't do that because each view is normalized separately. Besides, even when that works it does not explain the bright edge in the All Channels view.

As for the white area, compare the Histogram panel display to the one in the Levels Adjustment window, which still has a white area. Try changing levels there & then compare it to the histogram. Something still isn't right because they don't match up, whether comparing the Master vs. All Channels display or to any of the single channel views.

Ok, on mine the graphs are hitting the top so any normalisation is having no effect so they match my composite one exactly. 

As for the levels histogram ... mine are matching up well - obviously my levels one is a wider window so is slighly stretched in comparison and I did click on the little exclmaimation mark in the normal histogram to make it render more accurately (if you don't do this you may see an extra spike or two that shouldn't be there as it only renders a course histogram for speed). Comparing the master to all channels or individually mine are matching as far as I can tell and my eyesight allows!

Maybe there's something else at play here? You don't have the layer tickbox selected on the main histogram do you?



 

Share this post


Link to post
Share on other sites
31 minutes ago, markw said:

Hum… So can someone give an actual real world example where seeing this RGB overlap in  AP’s Histogram is useful ?
Right now it seams to me, that in terms of usefulness while editing and image, that blue overlay of RGB overlap might as well be telling me how much rain fell today.

I would refer you to R C-R's link to the cambridge tutorial in his post above. That explains a bit about it. There are some uses, mainly to detect clipping and contrast issues.

Share this post


Link to post
Share on other sites
4 minutes ago, Dazzler said:

Ok, on mine the graphs are hitting the top so any normalisation is having no effect so they match my composite one exactly. 

Try it with a photo or original artwork when one or more color channels does not go all the way to the top. Also, the differences I see between the Histogram & Levels windows persists whether or not the histogram is set to fine or coarse, & when the Histogram window is adjusted to match the Levels display width as closely as possible.

The Layer checkbox is not ticked on the Histogram panel -- if I do that with the Levels window open, the Histogram display shows nothing. Does that not happen for you?

Share this post


Link to post
Share on other sites
2 minutes ago, R C-R said:

Try it with a photo or original artwork when one or more color channels does not go all the way to the top. Also, the differences I see between the Histogram & Levels windows persists whether or not the histogram is set to fine or coarse, & when the Histogram window is adjusted to match the Levels display width as closely as possible.

The Layer checkbox is not ticked on the Histogram panel -- if I do that with the Levels window open, the Histogram display shows nothing. Does that not happen for you?

The layer checkbox just shows the histogram for the layer you have selected, so depending on what that is it may be blank, or might just be normal looking histogram.

I've found an image with varying heights between the normalisation, but still my graphs match well with the levels ones. I pulled one out of unsplash using the stock function - https://unsplash.com/photos/q3o_8MteFM0?utm_source=Affinity Photo&utm_medium=referral

How does that one work for you?

Share this post


Link to post
Share on other sites
9 minutes ago, Dazzler said:

How does that one work for you?

I just did a quick check & I apologize for the fuzzy jpeg screenshot, but this is what I am talking about:

1830137607_blueedge.jpg.de3e6627257c0d90699ccc6a82518fd7.jpg

When I compare that to the 3 individual channel views, I don't see enough overlap to explain why it is there in the All Channels view.

Share this post


Link to post
Share on other sites
16 minutes ago, R C-R said:

I just did a quick check & I apologize for the fuzzy jpeg screenshot, but this is what I am talking about:

1830137607_blueedge.jpg.de3e6627257c0d90699ccc6a82518fd7.jpg

When I compare that to the 3 individual channel views, I don't see enough overlap to explain why it is there in the All Channels view.

That's the green channel's edge - the green is behind the transparent blue channel. You can clearly see it joining the green unobscured layer on each side. It's also doing the same nearer the middle. Remember that the individual channels on this are normalised to the height of the chart, so when you view the green channel it gets stretched upwards, but it's the same shape as it is in the combined view (make sure you click the fine view - it looks slightly different in course view) - just stretched.

Share this post


Link to post
Share on other sites

Just to prove what I just said, I took the green channel view and pasted it over the combined channels and just 'un-normalised' (squashed) it down to the same size it was and you can see it's the reason that area of combined colour exists.

histogram.png.dea018e032d3a55e69820749a35a51d9.png

Share this post


Link to post
Share on other sites
On 11/26/2019 at 10:41 AM, James Ritson said:

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. 

Hi
I understand that Intensity Waveform is a better way to see the brightness and the current histogram overlapping,...
My question is whether it might be possible to display the histogram in the way Xnview does, being able to select luminance and RGB separately, as seen in the attached.

thanks :)

Luminance_xnview.jpg

Share this post


Link to post
Share on other sites
19 minutes ago, Alareta said:

My question is whether it might be possible to display the histogram in the way Xnview does, being able to select luminance and RGB separately, as seen in the attached.

Or at least to use something other than the black background in Dark Mode, like maybe the same medium grey used in the Light UI. As it is, the blue channel is difficult to see in the All Channel view.

I would also like to see a non-traditional All Channel view that just showed curves as bright lines without any fill below them, & when undocked that the panel could be expanded vertically as well as horizontally for a more detailed view.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

Please note the Annual Company Closure section in the Terms of Use. These are the Terms of Use you will be asked to agree to if you join the forum. | Privacy Policy | Guidelines | We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.