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alecspra

Converting and Editing color images in B&W, in LAB color space.

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Hi, I am still trying to figure out what is the most flexible and powerful method for converting and editing color images in B&W.

 

For the most part, I have been working in RGB, using the B&W adjustment and further tweaking the image with an HSL and sometimes a White Balance adjustment, both placed underneath the B&W layer. It works great.

 

But now I am experimenting doing the same thing in LAB. I don't quite understand if I should use the same approach as I do in RGB (described above) and whether the B&W and HSL adjustments work in the same way in LAB as they do in RGB. Or if there is a better way of doing the conversion and editing when working in LAB (by better I mean more flexible and powerful).

 

I would appreciate any insights you can share on this topic.

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Hi alecspra,

 

A little quicker way of getting a black and white image in LAB mode, if you click on the Channels panel you can right click on the Channel Background AOpponent and select Clear and do the same for Background BOpponent.  This should now leave you with a black and white image.  If you now apply a curves adjustment, you'll be able to alter the tone of the image.  This should give you different results to the methods you've used above.

 

I'm sure someone else will be along to give you a few more specific tips on the best methods to use.  

 

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Not a tip but attached is a macro that will do the steps @stokerg mentioned. It first hides & copies the selected layer for backup/safety purposes, renames the copy to "B&W copy," converts the file to LAB color format, & then clears the A & B opponent channels of the B&W copy layer.

 

Caveats:

1. If no layer is selected, it crashes my copy of Affinity Photo v1.6.6.

2. If a group layer is selected, it creates a "B&W copy" group layer, but the opponent channels of the layers in the group are not cleared.

3. If multiple pixel layers are selected (but not grouped) it creates a "B&W copy" layer for each of them & does clear their opponent channels.

LAB to B&W.afmacro


Affinity Photo 1.8.3, Affinity Designer 1.8.3, Affinity Publisher 1.8.3; macOS Mojave 10.14.6 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 
1.8.3.180 & Affinity Designer 1.8.3.2 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 13.3.1

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13 minutes ago, R C-R said:

If no layer is selected, it crashes my copy of Affinity Photo v1.6.6.

 

No crash here in 1.6.6 on High Sierra, same with 1.6.7 Beta 1 as well

 

Also, thanks for sharing the Macro, will be a time saver for anyone else wanting to play around with this method :) 

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16 minutes ago, stokerg said:

No crash here in 1.6.6 on High Sierra, same with 1.6.7 Beta 1 as well

I am running macOS Sierra 10.12.6 & for me it consistently crashes both AP 1.6.6 & 1.6.7 Beta 1. I can furnish crash reports for each to you but I would prefer to do that privately. Publicly, I will say that on both the Dispatch queue: com.apple.root.default-qos thread crashes & the exception code is "KERN_INVALID_ADDRESS."


Affinity Photo 1.8.3, Affinity Designer 1.8.3, Affinity Publisher 1.8.3; macOS Mojave 10.14.6 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 
1.8.3.180 & Affinity Designer 1.8.3.2 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 13.3.1

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11 minutes ago, R C-R said:

I am running macOS Sierra 10.12.6 & for me it consistently crashes both AP 1.6.6 & 1.6.7 Beta 1. I can furnish crash reports for each to you but I would prefer to do that privately. Publicly, I will say that on both the Dispatch queue: com.apple.root.default-qos thread crashes & the exception code is "KERN_INVALID_ADDRESS."

 

Feel free to PM me the crash reports or email them over to affinitysupport AT serif.com and put FOA Gareth in the subject and it will get me.  I'll also do some tests on our VM of Sierra and see if i can replicate the crash.

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9 minutes ago, stokerg said:

Feel free to PM me the crash reports or email them over to affinitysupport AT serif.com and put FOA Gareth in the subject and it will get me.  I'll also do some tests on our VM of Sierra and see if i can replicate the crash.

email sent.


Affinity Photo 1.8.3, Affinity Designer 1.8.3, Affinity Publisher 1.8.3; macOS Mojave 10.14.6 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 
1.8.3.180 & Affinity Designer 1.8.3.2 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 13.3.1

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5 minutes ago, MEB said:

The macro does crash on Sierra if there's no layer selected (just checked it on system running macOS 10.12.6).

 

Thanks MEB, saves me having to boot up the VM in the office. 

 

I'll get this logged for further investigation today and include R C-Rs crash logs :)

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Thanks so much for the LAB technique to convert a picture to B&W. 

 

I tried it and the limitation I see with it, is that once you clear the color Channels, you can't use the B&W, HSL or White Balance adjustments to further tweak the image. In other words there is less flexibility. You can change the tonality using Curves but you can't change the relationships between different tones, like you can with the other method.

 

I also tried comparing the same approach in LAB that I use when working in RGB (using the B&W adj + HSL), and it seems to give very similar results, at least visually. I am just wondering if, from a technical perspective, there is any difference worth considering, between working in either color space, specifically for doing what I just described.

 

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