Hoffmaster wrote:djui5 wrote:
Does GIMP process HDR images? If so I might download it. My version of Pshop won't do it.
No, I do not believe that GIMP will do HDR. But for a free program, it's every bit as good as PS, but without the "merge" ability for HDR.
I have not dabbled with HDR yet. I'm more of a fan of graduated neutral density filters which allow you to achieve close to the same result as HDR. I still suck at post-production work. As soon as I get CS3 I will try HDR. I'm even thinking about shooting some images this weekend for HDR. We'll see.
I've been a Linux die-hard ever since, well...a very long time. Anyway, giving up Photoshop was one of those things that came hard. I ran it under crossover office and wine for a while until GIMP got to its current maturity level. It's also taken a while to discover how to do things with the GIMP that I usually did with Photoshop, but to my pleasant surprise most of the things I used to need add-on filters in Photoshop to do the GIMP can do one way or another out-of-the-box. I try not to retouch images but I'm not good enough to get stunning shots with just me and my camera, so I've worked some of these things out on Linux. I wasn't going to post any of my HDR composites, but maybe I will, now. Here's a short tutorial on how to do High Dynamic Range images with GIMP:
I'm going to assume we're shooting something that is back-lit and is creating a great deal of dark silhouettes in the foreground. This needn't be the case, but it is the impetus for me to go to this technique more times than not. Step one is to take a few stock shots of the image using different aperture times. Since everyone probably knows how to do all of this already I won't goo into too much detail. Sufficed-to-say: You'll have better luck using some kind of tripod and trying to get the same shot with different exposures each time so that you don't have to line all of them back up later and worry about sizing problems for objects in view. I'm going to assume you don't have to line the shots back up for this tutorial. Next we take the stock shots over to GIMP...
After downloading the image series to my box the very next thing I usually do before going any further is renaming all of them I want to use by their exposures, something like: "Saguaro_Cactus_Darkest.jpg", "Saguaro_Cactus_Dark.jpg", "Saguaro_Cactus_Medium.jpg", and on and on until they form a logical series. Then, launch the GIMP and open the "middle" shot, that is - the shot that was taken with a normal exposure as if you had just walked right up and taken it without adjusting the aperture...
This middle image will now be your composite image, or your "workspace image" depending on the school of thought you subscribe to. Open your dark stock image (underexposed image) in a new window and do a "select all" and "copy". Now return to the composite and create a new layer by choosing "Layer" -> "New Layer." I usually change the layer names to keep track of them, in this case I'd call it "Dark Layer" or something. Paste the dark stock image into this layer and hit the anchor control. What you should see now in the composite window is just the dark image. That's good...
Now, return to the dark stock image window. Leave the composite window open. To make it into a mask we have to convert this image to greyscale, so choose: "Layer" -> "Colors" -> "Desaturate". You should now have a greyscale image with the overexposed parts opaque and the correctly exposed darker parts transparent. This is going to form the basis for the layer mask we'll apply to the composite. The transparent darker areas will become visible in the composite, soon. First-things-first, we need to brighten up the image, slightly. Here's where the art comes in and this will require a lot of experimentation. Go to "Layers" and choose: "Colors" -> "Curves". A box will pop up with "histogram" representing the color saturation of the image. It should also have a little preview box near the upper window border. Pay close attention to that preview box and look for the "peak" in the histogram at the bottom of the window (It will look like a profile of a mountain range, find the tallest point). Click on the line above that tallest section and drag the line toward the top of the box. How much or little to drag the line depends on your preference, if you drag it a lot you will use more of the dark stock image in your composite; if you drag it a little, you will see more of the "medium" image. Draging it all the way to the top of the box creates the most pronounced HDR effect. Play with this and see what you like, watching the preview box for an estimate of what it will do. When you're done manipulating the mask perform a "select all" and "copy" and return to the composite (middle) image...
Back at the composite image, open the "Layers" window if it isn't already open by choosing: "Ctrl-L". In the "Layers" window (not the composite window) right-click on the "Dark" layer and choose: "Add Layer Mask". You can leave the settings as they are and click "Ok". Now, making sure you haven't clicked on the other layers, choose: "Edit" -> "Paste." Click the anchor control in the layer window to anchor the layer mask you just pasted. The composite image should now have less silhouette in the dark areas and the lighter parts should be unchanged. Overall it should appear more vibrant than before. You can remove the pasted mask and return to the dark image if the change is too subtle or too pronounced for your liking. Just play with the histogram and copy-paste the mask over onto the composite, as before, until you get what you want...
Close your dark image, if you're done with it, and open the "light" image (the overexposed one) in a new window. Leave the composite image open, of course. As before, select all of the light image and copy it. Return to the composite image, create a new layer called "light" and paste the light image into that layer. Return to the light image and once again perform: "Layer" -> "Colors" -> "Desaturate." Here's where it gets a little tricky, and this step is hard to remember. We can't simply manipulate the curve here and use it as a mask because it would result in the composite using the bright parts of the bright image and dark parts of the dark image, which is opposite of what we're trying to accomplish. Instead, choose: "Layer" -> "Colors" -> "Invert". Now we'll get the effect we want. If you need to do additional brightening on your light image (probably won't be needed) then follow the steps to adjust the curve, as before. You can also darken it if you want to by dragging the histogram line down rather than up. Copy this mask and return to the composite image. Right-click on the "light" layer and create a new layer mask like you did for the dark layer. Paste the mask into this new layer mask and click the anchor control. Your composite image should now have a bright blue sky and much cleaner colors.
You can now save your new, GIMP-produced, HDR image as a flattened JPEG. I usually save the layered composite in a GIMP-friendly format for later manipulation. Compare it to the original "middle" image for more dramatic effect. Play with the histogram and don't be afraid to delete layers and start over. I recently made one that turned out pretty well using three different exposure settings darker and lighter each way from the middle image and then going through all of the steps above to create a composite out of the seven. Just remember to invert those shots that are lighter than the middle when making the light-image masks. If I get time later maybe I'll post some screenshots to go with this tutorial...
Have fun!
Jeff
