photoshop "gradual" brightening

[markogts]

Hi all!

A typical problem with panoramas is that the upper part of the picture is too bright, while the lower is too dark. You can help yourself with the "magic wand", of course, but so you get nasty "steps" of brightness. I was thinking if it was possible to do, let's say, two variations of the same picture: the brighter and the darker one (created with "curves", f.e.). Then, to blend them in such a manner that the upper part of the resulting picture has 100 percent of the bright picture's pixels, the lower part 100 % of the darker one, and the pixels in the middle of the picture progressively, gradually changing (with an interpolation, let's say) from one extreme to the other.

Hope I cleared what I mean. In case, let me know, I'll try to explain better. Any suggestions?

[green]

Here is what I do:

- Create two occurence of the same picture; one darker (for the sky) and the other brighter (for the ground).

- Arrange them into 2 differents layer (say the well exposed sky or darker picture is the bottom layer and well exposed ground or brighter picture is the top layer).

- Use the eraser tool with a very soft edge and erase the overblown sky of the top layer to let appear the well exposed sky from the bottom layer.

- Flatten the layer.

[markogts]

Thank you. I tried as you suggested, but it's very difficoult to avoid artificial spots of light with the brush.

I was thinking of creating a layer with the correction layer (darkening with curves). Then, in layer style, I select gradient overlay. But, instead of getting the overlay between a darker and a righter picture, get an overlay between the brighter picture and a uniform white-to-black gradient. There has to be some options in the blending mode or some different ways of creating the layer that I don't know.

[green]

Why don't you send me the picture so I can give you a try and then I'll let you know how I did it.

[Mike]

Best way to achieve your goal is to use an alpha mask.

Create a new layer and fill it with a black to white gradiant fill.

Go to the channel dialogue box and duplicate any one of the RGB channels of this gradiant layer.

Load the duplicated channel into memory by using Select/Load Selection

Now go to the layers pallete and switch off the gradient layer, making sure that the picture layer is selected.

When you now alter the image with whatever method you choose (curves/levels etc...) you'll find that it alters the image incrementally, based on the mask that is loaded into memory, in other words, the top half of the image receives more adjustment than the bottom (or vice versa).

[markogts]

... what I was searching for. Tomorrow I'll upload the original and the corrected photo, so you'll see. Thank you wery much!

[markogts]

however, tomorrow I'll post both the original version and the corrected one, so you can try your technique which, I suspect, is more dependent on personal skills, while the one proposed by Mike is almost purely mathematical.

[Mike]

Happy to help Marco, alpha masks (or graduated masks as they are sometimes called) are extremely powerful, and you're not limited to simple black to white linear gradiants, you can use shapes too just as easily, you can also use the loaded mask to do some very creative manipulations, fading a colour image to a black and white one, or adding a tint just like a coloured filter on a traditional lens, the sky really is the limit, if you can imagine it you can usually create it with an alpha mask!

[markogts]

Hi Mike! I posted both the original and the masked versions <a href="http://www.trekearth.com/gallery/Europe/Italy/photo99115.htm">here</a>. Thank you again.

You know, I was starting from a wrong point. I was trying to create two pictures (bright&dark) and to blend them in some particular way. Your way works perfectly, but I have to admit that all the procedure still appears a bit "black magic" to me. I'll excercise :-)

[markogts]

...you can find it <a href="http://www.trekearth.com/gallery/Europe/Italy/photo99115.htm"> here </a>. Thank you!

[green]

I think Mike process works very well actually better than mine. I might use it myself.

[Mike]

I'm glad you managed to get the general idea from my brief instructions, it can be quite tricky to get the hang of what is actually going on at first.

Here's a very good site that explains alpha channels in much more detail, along with illustrations, it should make things much clearer!

http://www.cahe.nmsu.edu/bchamberlin/alphachannels/intro.html