Elle Stone's tutorial, Autumn colors

Processing
17

I haven’t touched this tutorial since it was first written, so I am a little rusty. And it has been updated since, along with GIMP, etc. … :man_shrugging: Here are my thoughts:

When I open the XCF, I immediately encounter an issue. It is one that I have noticed all along but haven’t asked about yet.

image

Let me tell you what it is in case you can’t tell by the image. To GIMP, this image has a perceptual gamma. This becomes apparent when GIMP confronts you directly with

image

But I don’t want to convert! My workaround would be to create an empty image with the same profile but set to linear light and 32f, and then open as layers the XCF. Is there a better way? (@paperdigits @Morgan_Hardwood please follow up my post wherever I write “my workaround”.)

Let’s get to where @Underexposed is stuck. Take a look at @Elle’s screenshot.

image
image779×674 156 KB

See how there is only one masked layer, besides the untouched scene-referred one? Well, that is where all the steps go toward in C1.

Step 3 is where it begins to be tricky. To my understanding, you can only apply profiles to the whole layer stack. When I extracted LAB B, I could not find a way to apply LABL to that one layer. My workaround would be to do Image → Duplicate to create a copy of the whole stack and then select and copy the layer’s image back to the original stack. Don’t forget to convert from LABL back to g10 before you do the copying. (Just remembered that I didn’t do that.)

What you delete is the extracted LAB B layer. You don’t need that anymore; you have the LABL LAB B now.

I am uncertain about step 5 but I think we are supposed to select the LABL LAB B layer and make a grey scale mask on it using its grey scale so that we are able to make selection from mask. Then you use this selection to make a mask for “Visible + Channel mixer to add Chroma”.

Now you delete the LABL LAB B layer because you don’t need that either. Now the result should be similar. It won’t be the exact same for the reasons that @Elle has stated in her article and website, and because our setup might be different in obvious or subtle ways.

Mind blown. :exploding_head: I feel my body contorting just by writing this post. I hope I didn’t mess up the explanation because of that.

1 Like
18

Why?

19

This is because the profile is already linear gamma.

20

I followed the steps as indicated.

Instruction B4.:

  1. Open the image and promote the precision to 32-bit floating point.
    If you convert to integer precision, many of the editing operations used in this tutorial will clip intermediate editing results. This “integer clipping” will completely defeat one of the goals of the tutorial, which is showing you how to work with out of gamut channel values.

  2. If you are using default GIMP 2.9, convert the image to GIMP’s built-in sRGB color space. If you are using CCE, make sure the image is in the linear gamma RGB working color space of your choice.
    The downloaded XCF file is in the linear gamma sRGB color space.

There will be very slight differences in the Chroma of the final image when processed in different linear gamma RGB working spaces because Channel Mixer is a chromaticity-dependent editing operation. Because of how Channel Mixer is used in this tutorial, the differences in the final image won’t be noticeable.

21

I think @afre either converted to 32-bit floating point and buit-in sRGB, just in a different way: he opened a blank image file in 32-bit float and then opened the original xcf file as layer. This will convert to what we want.
I guess.
Just don’t understand the reason for that workaround

1 Like
22

To apply the V4 RGB working space profile:

C1.3.2 Extract the B channel using “Colors/Component Extract” and select the LAB “B” channel. Change the layer name to “LAB B channel”.

C1.3.3 The resulting extracted layer will have the wrong tonality because the “Component Extract” procedure doesn’t take into account the TRC of the layer stack. So drag the B channel layer out as a new layer and assign to it a V4 RGB working space profile from my profile pack that has the “LAB L” companding curve. These profiles all have file names ending in “-labl.icc”.

Drag the resulting layer back to the original layer stack. Go ahead and delete the originally extracted layer.

I dragged the “LAB B channel” layer down to the bottom of the whole stack and changed the profile there. Then I dragged it back.

23

C1.3.4. Drag the resulting layer back to the original layer stack. Go ahead and delete the originally extracted layer.

I took originally extracted layer to mean the layer labelled “scene-referred for LCH Chroma group.” At the end of step C1.3.6 my stack looked like this:

6%20

And the image looked like this:

6%20

In that image, I see a lot of bright orange, green, and some yellow pixels that are not in the Blended result Elle showed. Her image also appears to me to show effects of the Grayscale mask, but I don’t see that in my image.

My discrepancies only get worse from here once I start working on the Lightness group layers.

24

How did you do that? In Image → Color Management? If so, you’re not only converting that layer’s profile, but all layers. I think that’s not what Elle’s meant to do. In that case, @afre’s second workaround (Image → Duplicate) makes sense.

25

I never checked the other layers until now, and you are right. They are all sRGB-elle-V4-labl.icc.

I have no idea how that affects things. I will have to look at @afre 's second workaround and try it out.

I’d like to see what his image at the end of C1.3.6 looks like.

26

I just heard from Elle. She’s seen this thread and had started a revision of that post a while back. She’s hoping to finish it and update it later today for GIMP 2.10 (w/o referring to GIMP CCE). The screenshots may be out of date, but the text process should reflect the updates.

3 Likes
27

Well, I’m still at the very beginning of the learning curve, but changing all layers to a smaller collor gamut will certainly affect it (in a bad way).

And good news from @patdavid, above (Thanks, Pat!). You made it, @Underexposed!

28

Autumn is a state of mind - wind, grey sky … even in July

Complete post-treatment: colors desaturated.

1 Like
29

However, as you can see from the screenshot, GIMP thinks sRGB-elle-V4-g10.icc is perceptual gamma (sRGB TRC). We don’t want to go from perceptual to linear during depth conversion. We only want depth conversion.

Screenshot again, for your convenience.

image

1 Like
30

@beachbum this was edited according to Elle’s workflow?

31

That’s the best news @patdavid. Thanks.

Tried doing this, but not sure how the layer’s image was copied and put into the original image stack. The result of all the maneuvering seems only to be a selection mask on the Visible + Channel mixer to add Chroma layer, since when you delete the “LAB B channel” layer, any other effect of it disappears. I followed the original instructions, including the profile change, but once I had the selection mask, I changed the profile back and deleted the “LAB B channel.” Didn’t seem to help.

I look forward to the updated tutorial.

32

I did learn why the result of step C1.3.6 does not match Elle’s screenshot of the blended result. In the instructions for extracting the LAB B channel, she did not include, “making sure to check the ‘Invert component" box and the "Linear output’ box,” as she does elsewhere when discussing making a Chroma mask. (Modify saturation using GIMP's LCH color tools)

The bright oranges, yellows, and greens are gone.

6%20with%20extraction%20inverted%20and%20linear%20output%20

1 Like
33

I am not prepared to break down the steps for you right now. I have had a tiresome week and discuss has been a good distraction. I think I have left enough cookie crumbs. Maybe someone else could lend a helping hand. :wink:

Your conclusion is wrong. The purpose of the mask is to isolate the organics so that you may tweak their chroma. If you invert the mask, then you would be working on the inorganic regions.

35

Hi All,

My apologies, my Autumn Colors tutorial was written in 2015. Since then so much has changed in default GIMP, rendering the original tutorial no longer workable even in later versions of GIMP 2.9, much less in 2.10.

The original 2015 version of the tutorial used “Colors/Components/Decompose to LAB” to make the original Chroma mask, using the “B” channel. But when I started updating the tutorial several months ago I switched to “Colors/Components/Extract Chroma” thinking this would be easier. But actually this left the tutorial completely “broken” in the steps to increase Chroma, because it turns out that extracting the Chroma channel clips channel values to the range 0.0-1.0f.

In the last two days I’ve updated sections A, B, and C. I just now uploaded the new text and screenshots and also uploaded new downloadable xcf and curves files. I’ll work on the remaining sections over the next days.

If @Underexposed hadn’t started this thread no doubt many more months would have gone by before I noticed anything wrong with my “Autumn Colors” tutorial. Which would have been a shame because the techniques that are described really are useful for editing and also for painting, and AFAIK no other image editor than GIMP allows quite this type of editing. So @Underexposed - thank you! for having the patience to work through the tutorial and explain the problems.

Hopefully the revision is a lot easier to follow, and if not please let me know and I’ll attempt to remedy the remaining issues. Various people in this thread have raised various issues, some of which I’ve tried to work into the tutorial, and others I’ll try to answer here in this thread.

Best,
Elle

2 Likes
36

Hi @afre and @Underexposed - actually you are both right!

In the original 2015 tutorial I used the LAB “B” channel as the initial Chroma mask, to isolate the sky, as the sky was very positive in the “B” channel and somewhat in the shadows cast by the trees, but not elsewhere. The “B” channel mask made it easy to target the amount of saturation added to the sky, by adjusting channel values in the B channel that were greater than middle gray. And then I used the Chroma channel to make selections to further modify the “B” channel mask to lower the highest Chroma colors in the orange and yellow leaves on the trees. This was a fairly complicated way to make a Chroma mask, and I didn’t explain all the steps even in the original tutorial. I just provided the final Chroma mask instead.

In the revised tutorial I skipped using the “B” channel entirely and just used the LCH “C” channel to make the initial Chroma mask, which requires inverting the “C” channel to mask the highest Chroma areas more than the lower Chroma areas.

1 Like
37

Definitely, it would depend on what you are doing and what your goals are. Now that you are back, I will retire from customer support. :sunny: Let us know when your updates are complete.