Channel editing

[Hoogo]

... I still think there is some voodoo involved, especially in the negative percentages/subtracting less than zero etc...

Maybe another way to think about negative values: Think of averaging with an inverted channel, and imagine how contrast fades while you slowly add more and more of that inverted channel.

The method I followed for anyone faced with similar damage draws heavily on Ctein's techniques (see here) and...

Yes, that's somehow similar. 2 channels, where the stains appear in a different way, and mixing them with some feel. I think I thought about creating a mask that way at the end of the lens flare thread, but didn't finish it. You can even calculate the perfect percentages of the channels when you have the RGB values of a good and a matching bad spot.

4. Now tweak the R/G/B channel curves. I have to admit the voodoo failed me here and I borrowed heavily from Ctein's advice, which was "The red curve increases the amount of cyan in the measles, while the blue curve reduces the amount of yellow.

It becomes more easy when you do it channel by channel. Turn off the view of all but one channel, maybe add an adjustment layer "histogram correction" to temporarily better spot differences in the picture.

[photoken]

...
I have now used a similar but more sophisticated mask then adjust channels layer method on another damaged image, this time with 'measles' spots (lots of orange brown speckles).
...
The method I followed for anyone faced with similar damage draws heavily on Ctein's techniques (see here)

There are many, many methods of retouching available in our digital age. Some of the techniques found on the Web are rather old and have been superseded by newer techniques that are easier and faster. Specifically for your image spots, PL has an action named "Frequency Filter" that works great for removing spots and blemishes (particularly on skin). It is the technique also known as "Frequency Separation".

Also, the other examples in the file you cited can be retouched using completely different techniques available in PL, such as the DeHaze filter, etc.

[cathodeRay]

Hoogo - imagining an inverted channel works for me, insofar as an inverted channel is a sort of opposite, other (negative) side. (Well actually it is an opposite). The idea of being able to calculate and so dial in the numbers (percentages) was as I am sure you have realised part of my original plan, the idea being to reduce the amount of time squinting at the screen to see which way a colour needs to go.

Ken - I agree there are many ways of doing things - a blessing and a curse. Ctein's online version of the measles repair is from the first edition of DRfStF; I have the second edition (which has less on measles fixing) and it is said a third edition may be on the way. It will be interesting to see what he does and doesn't update.

One of the hurdles in PL as many know only too sell is the brief cryptic manual. Some help as far as it goes, which isn't very far. This forum is of course a superb source of knowledge about PL, but it is all too easy to feel a bit silly asking repeated questions! That's one of the reasons why I try to put something back, so instead of saying (as others do on other fora) 'problem solved' or 'I've fixed it now', I try and give an account of how I fixed it/what I did - hence the recent 'recipe' in this thread.

What I think would be really helpful is a problem orientated guide manual, or even just a list: eg 'If you have measles spots' (or rather your image does, if you do you'd probably be better off calling your doctor) 'then try these: Channel Mixer; Frequency Separation; xxx etc'. It's often not immediately obvious from the name what an effect/filter does. The description for the Frequency Separation action is 'Splits an image into three layers containing low, middle and hight frequencies.The used radii are dependant of image' - very helpful as far as it goes, but doesn't mention purpose!

BTB - it seems a pity actions.actions appears to be in some sort of binary format, rather than text. It would be so useful to be able to go in and tweak things. And while I'm on actions - the 'save/save as' limitations (covered previously elsewhere by others) are frustrating! I make an action to save reduced size jpg ffrom big 16 bit tif - and each time I use the action it overwrites the previous save with the 'recorded' filename! Setting it to open the 'save as' dialog is a workaround, but rather defeats the automation point of actions.

cathodeRay

[photoken]

BTB - it seems a pity actions.actions appears to be in some sort of binary format, rather than text. It would be so useful to be able to go in and tweak things.

You can edit the components of an action in the Action panel and save your new action.

[photoken]

What I think would be really helpful is a problem orientated guide manual, or even just a list:

As users, we can help by using this forum to explore the various features of PL and share our results.

Maybe it's time for another Experiment? I'll start a new thread for Experiment 05.

[cathodeRay]

Ken - I have now realised you can drag and drop actions in and out of groups etc so you can new ones as well to a group and I know you can double click one to change the dialog settings but I just like the simplicity of editing a text file.

The experiment sounds like an excellent idea, but with Christmas just round the corner it might town out a bit of a turkey... hope not though!

cathodeRay