Re: [Gimp-developer] GIMP useability - choosing linear vs perceptually uniform RGB

[Elle Stone <ellestone ninedegreesbelow com>]

On 05/01/2015 07:03 PM, Gez wrote:

> You chose one of the few cases where both linear and perceptually
> uniform could be valid options and none of them are right or wrong.
> Of course I'm not against allowing two valid instances of the same
> thing, like in this case.

I've already given other examples.

> But you're not proposing to add a toggle to gradients alone, you're
> proposing to put them*everywhere*.

Yes.

> I'd like to see this discussion heading towards a real world list of
> examples of real needs for such options that can't be satisfied with
> anything else than these toggles.

You are presupposing that the devs can foresee every possible use to 
which a user might put a given editing operation.

Currently the user does already have linear vs perceptual choices 
through the GIMP UI for most editing operations (scaling is always 
linear, drawing a gradient is always perceptual).

Currently the user can use or not use the gamma hack. And the user can 
use linear or gamma precision. That's two time two equals four 
possibilities for the user to try for each and every editing operation.

Now tell me without taking the time to try all four possibilities:

How does the user get a linear gradient? (sorry, you can't)
How does the user get linear gamma channel mixer?
How does the user get perceptually uniform Filter/Noise/Add RGB noise?

I'm proposing to make the current GIMP UI for switching between linear 
and perceptually uniform RGB much simpler and clear to use:

1. Eliminate the precision switches by putting the linear vs gamma 
choice on each layer, rather than having to convert the entire layer 
stack to a new precision. This will have the side benefit of cutting the 
number of precision dialog entries in half.

2. Replace the gamma hack dialog with a "Linear/Perceptual" switch or 
drop-down menu that shows the default setting that was set by the devs, 
and also allows the user to quickly and easily choose the other setting.

Right now the babl flips and GIMP UI give the user a choice, at least 
for most editing operations. But how to get linear or perceptual out of 
any given editing operation isn't at all clear.

The current UI wasn't ever intended to be permanent and does need to be 
redesigned. The babl flips and GIMP UI can be redesigned to:

* Prevent the user from making an edit on linear RGB if the devs decide 
the particular editing operation "should" be done on perceptually 
uniform RGB.
* Prevent the user from making an edit on perceptually uniform RGB if 
the devs decide the particular editing operation "should" be done on 
linear RGB.

Or the babl flips and GIMP UI can be used to provide the user with the 
same choices that users of PhotoShop and Krita and every other high bit 
depth image editor already have: which is to perform all edits on either 
linear or perceptually uniform RGB.

In PhotoShop, Krita, etc, the only way to change whether the RGB data is 
linear or perceptually uniform is by doing an ICC profile conversion.

In GIMP the UI could be designed so the switch between linear and 
perceptually uniform can be done easily on a per-op basis, if the UI 
were redesigned the way I am suggesting, or some way that provides 
equivalent functionality.

Or in GIMP the UI could be redesigned so the switch between linear and 
perceptually uniform is taken completely out of the user's control.

I fail to see any advantage at all to giving the user a choice for some 
operations and not for all operations. It places the devs in the 
not-so-nice position of having to know in advance all possible uses to 
which the user might want to put all possible editing operations.

> > Why do you want to put roadblocks in the user's way?
> There are certainly rights and wrongs when using a tool. If the tool is
> designed to work some way and you don't respect that, you're doing it
> wrong.
> Try taking a hammer upside-down and hammer nails with the handle.
> That's wrong.

Sorry. Not a good analogy. Like all tools, a hammer is a means to 
accomplish a goal, nothing more, nothing less. The precise goal, and 
hence the right way to use the hammer, depends on the goal of the person 
using the hammer.

Not every problem for which a hammer is a good solution happens to be a 
nail:

Maybe you want to mold some soft metal into a curved shape and the 
hammer's handle happens to be the right shape for the task.

Maybe you are using the hammer to hold something in place so you can 
accomplish some other task. Recently I used a sledge hammer to hold down 
a spring-clipped cover so I could access some bolts hidden behind the 
cover. Should I have gone to the store and asked for a "heavy duty 
spring-clipped cover holder downer"?

Maybe you want to reset a nail that is coming out of place, but you use 
the side of the hammer to gently press the nail back in place because 
you don't want to further damage some old and rotted wood.

The person who made the hammer doesn't and can't know all the inventive 
uses to which the person who buys and uses the hammer might think up 
along the way. And the developer who programs Curves, Channel Mixer, 
Gaussian Blur and etc doesn't know all the creative uses to which the 
person who uses these editing functions might think up along the way.

Best,
Elle