HDR Layer Masking in CS3

[ollypenrice]

Many thanks to all who helped me sort myself out over this. As requested, here's a 'How To' of the process I ended up following for my recent M42 image.

Objective; to combine images of different duration in order to cover a high dynamic range (HDR), a problem always encountered in M42 and often in galaxies. In Photoshop 7 it was easy, or at least familiar. Things have changed in Ps CS3.

-Shoot 3 exposure durations. I used 10 secs, 60 secs and 5 mins. I think maybe 12 or 15 secs might have been better. The Tak is about f5 so adjust accordingly.

-Open 2 images which we'll call the Long and the Short.

-Select, Copy and Paste the short onto the long. It is best to have co-registered them first but you can do it now; make the top layer only 50% opaque and push it around till it ligns up. Then go back to 100%.

- In Layers click on Layer Mask icon, the little rectangle with a circle in it.

-NOW GO TO CHANNELS. This is what's changed!

-Alt click on the white mask rectangle in the layer mask channel and have only that channel visible (using the eyeball symbol. De-eyeball the other channels.)

-Ctrl V to paste the short onto the white mask screen. It shows in grayscale.

-Go to Wndow>Arrange>New window for Short. In this window you will see what your work in progress looks like but you will work on the gray mask image, not the new window. However, you will be looking at the new window while mutilating the mask.

- In Filters put a huge Gaussian Blur on the mask image. About 30?

- In Curves grab the graph and haul it around like crazy while looking at the result in the new window. You will soon see what changes have what effects. When you get it right the Short comes through the mask in the right places to fill in the burned out sections of the Long image.

-When happy, Flatten Image and Bob's Yer Uncle.

In the end it is very much the same as PS7 but some relocation of functions had me beaten for a while.

Thanks again, really thanks, for all the help.

Olly

[jgs001]

Thanks for the info Olly, that's really useful to know.

[Beardy Bob]

Yep. I had no idea how to do it in any version of PS! Cheers!

[brendant]

A very useful technique Olly, thanks writing up the detailed method and sharing.

Brendan