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[aPhoto Windows] Curves Adjustment - Multiple Point Selection


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I have a curve adjustment layer and want to move two of the points at the same time. But i can't manage to select both points simultaneously - i tried Shift+Click, CTRL+Click, Alt+Click - nothing works.

I can't google this issue, because all i get is vector curves topics.

Please help.

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Why do you want to move them at the same time, rather than individually, @sveto?

-- Walt
Designer, Photo, and Publisher V1 and V2 at latest retail and beta releases
PC:
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It's part of my workflow. I often establish a good combination of contrasts for different parts of the curve that i like and then want to raise or lower a broader part of the curve without destroying the relation between the points.

I find your question a bit strange. Is advanced use of curves so uncommon here?

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18 minutes ago, sveto said:

I find your question a bit strange. Is advanced use of curves so uncommon here?

I can't speak for others, but I've never adjusted more than one point at a time.

-- Walt
Designer, Photo, and Publisher V1 and V2 at latest retail and beta releases
PC:
    Desktop:  Windows 11 Pro, version 23H2, 64GB memory, AMD Ryzen 9 5900 12-Core @ 3.00 GHz, NVIDIA GeForce RTX 3090 

    Laptop:  Windows 11 Pro, version 23H2, 32GB memory, Intel Core i7-10750H @ 2.60GHz, Intel UHD Graphics Comet Lake GT2 and NVIDIA GeForce RTX 3070 Laptop GPU.
iPad:  iPad Pro M1, 12.9": iPadOS 17.4.1, Apple Pencil 2, Magic Keyboard 
Mac:  2023 M2 MacBook Air 15", 16GB memory, macOS Sonoma 14.4.1

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What editing app allows selection of more than one point on a curves adjustment? I've looked at all the ones I have, and they all only allow selecting a single point.

Affinity Photo 2.4..; Affinity Designer 2.4..; Affinity Publisher 2.4..; Affinity2 Beta versions. Affinity Photo,Designer 1.10.6.1605 Win10 Home Version:21H2, Build: 19044.1766: Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz, 3301 Mhz, 6 Core(s), 12 Logical Processor(s);32GB Ram, Nvidia GTX 3070, 3-Internal HDD (1 Crucial MX5000 1TB, 1-Crucial MX5000 500GB, 1-WD 1 TB), 4 External HDD

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4 hours ago, sveto said:

Is it possible to stack adjustment curves without degrading the data, provided i work in 16bit?

I'm not sure what you mean about degrading the data but you could stack as many Curves Adjustment layers as you want. For example, create one, select it, & duplicate it several times, then adjust each one as desired.

417354134_CurvesAdjstacked.jpg.33e47c064a26c60769d39c9fbc33ac4c.jpg

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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I know that i can stack them. My question was if i'll get rounding errors and/or artifacts when pushing around the same tones multiple times in a row. I always work in 16bit per channel, but maybe it's not advisable to stack different curve adjustment layers on top of each other.

I need a clarification, because i'm looking for a workaround for not being able to select multiple points. I had the idea to do my fine adjustments on one curves layer, and then some coarser adjustments on another, etc.

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I think the only way to see if you get artifacts is to try it. 

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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Am i expected to do multiple technical tests to determine if the software can deal with advanced editing? Do you realize that some artifacts could remain invisible until later in the workflow when you can't go back anymore because you are approaching the deadline?

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2 minutes ago, sveto said:

Am i expected to do multiple technical tests to determine if the software can deal with advanced editing? Do you realize that some artifacts could remain invisible until later in the workflow when you can't go back anymore because you are approaching the deadline?

What I mean is depending on what you consider an artifact, the number of adjustment layers you add & how each is set, the results would most likely be different for different images you apply them to.

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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Well, i meant things like posterizing or color shifts. Very difficult to detect with the naked eye until (if) you do some serious further processing.

Isn't this an official forum? I'd normally expect people from Affinity to help here. Sadly, when it comes to the more technical issues and/or questions, i feel ignored.

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I guess I do not understand what you mean because Curve Adjustments inherently create color shifts. What else would you use them for?

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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Ever done adjustments in 8 bit per channel? Ever saw the image degrade? That's what i mean. And probably other things that i can't think of.

I guess in 16 bit it is safe enough to stack 2 or 3 curve adjustment layers, but you never know. That's why i'm asking. I appreciate you trying to help, but i'd rather hear some statement from the Affinity staff, because they should know the technical details, right?

But they rarely read this forum, or do i have the wrong impression?

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8 or 16 bit, Curve Adjustments inherently create color shifts. Thus my confusion about what you mean by degrade.

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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Rounding errors? (In the audio world we edit in 32 bit floating point resolution, just to avoid rounding errors.)

I don't know how much rounding errors play a role in image processing in 16 bit per channel data. That's why i'm asking.

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How would you define a rounding error in terms of the result? IOW, whatever the bit depth, a pixel can have only one color, right? So what would the magnitude of the error be in terms of the difference from whatever you would expect the resultant pixel color value to be? Unless it is more than one LSB, there would be no error, right?

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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What I mean is you are the one adding several stacked Curve Adjustments layers, presumably to get some result you could not get with a single one. So to you what would constitute a rounding error in this process & how would it cause problems, either now or later on?

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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If i could define that i wouldn't be asking. And as well - i wouldn't be asking if the software didn't force me to do that, given that i can't select multiple points in an Af.Photo curve.

My question is meant to prevent me from doing harm to my files that i could discover only later. Hell, even normal adjustments are hard to see when the eyes are tired.

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13 minutes ago, sveto said:

If i could define that i wouldn't be asking. And as well - i wouldn't be asking if the software didn't force me to do that, given that i can't select multiple points in an Af.Photo curve.

I don't understand why the inability to select more than one point on the curve at a time forces you to use stacked Curve Adjustments layers. What is it that you can't do, even if you have to adjust one point at a time?

17 minutes ago, sveto said:

My question is meant to prevent me from doing harm to my files that i could discover only later. Hell, even normal adjustments are hard to see when the eyes are tired.

Adjustment layers are non-destructive, meaning you can edit or delete them at any time. So how could using them cause harm to your files?

It all still boils down to how you define whatever it is you are trying to avoid, whether you call it harm, artifacts, defects, degradation, or whatever. Without a clear understanding of what you mean by that there is no way to answer your question.

All 3 1.10.8, & all 3 V2.4.1 Mac apps; 2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.10.8; Affinity Designer 1.108; & all 3 V2 apps for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 15.7

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