Dataset.image should be callable by element names

[iliiliiliili]

Dataset.image can be only called without parameters to convert all convertible data to image or with flags (True, False, True). We should also be able to call it with names: ds.image("image_2")

[LukasHedegaard]

I agree with @iliiliiliili , that ds.image("image_2") is prettier than the flags.
The "positional" behaviour is currently used for multiple functions:

• image
• numpy
• reshape
• image_resize

We should decide between the "positional" behaviour (flags) or using keys.
To give an example, we're deciding between

ds = ds.named('label', 'image')
ds.reshape(False, new_shape)
ds.reshape(None, new_shape)

or

ds = ds.named('label', 'image')
ds.reshape(1, new_shape)
ds.reshape([1], new_shape)
ds.reshape('image', new_shape)
ds.reshape(['image'], new_shape)

What do you think, @clegaard ?

[clegaard]

I strongly favor option 2 since it is more readable in my opinion.

[LukasHedegaard]

It seems we're in agreement. I'll include the fix alongside the new image transformations after Easter.