Easy Manual Exposure Blending with The Gimp

We talked about a simplified and easy 2 layers exposure blending in the last article and so here it comes. In most scenes the dynamic range of the scenes are just slightly out of range of the image sensors' dynamic range.  Therefore, we only need to extend the highlight or shadow area by about 2  to 3 stops and the 2 layers blending method can handle that easily.

Easy Manual Exposure Blending With The Gimp.
This image of the The Western Courtyard of The Curve Mall created using the 2 layers manual exposure blend with The Gimp was fast and reasonably good. -- Camera: Olympus Pen E-P1, Lens: M.Zuiko Digital 14-42 mm f/3.5-5.6 II standard zoom, setting lens zoom at 31mm and f/4.9, ISO 200. The shutter speed of the two blended images are 1/15s and 1/60s.

In this 2 layers method we use the +1 EV and the -1 EV photos from the three bracketed images. The 0 EV or "normal exposed" image from the camera is not required here. The +1 EV overexposed image has enough details to cover most of the scenes from the very dark to the mid-tone area. The high light details can be easily blended in from the -1 EV underexposure photo.

We use layer mask to hide or display areas where we want the image to be hidden or displayed. A black mask will display what is from the bottom layer and a white mask shows what is on the current layer that is connected to the mask. With that in mind we got another hint to simplify the 2 layers exposure blending method further.

The pillars of the western courtyard in Easy Exposure blending with The Gimp
The Western Courtyard pillars is in an open area receiving strong sunlight the rest of the courtyard is in dark shadow. Without exposure blending it is hard to get an evenly exposed image. -- Camera: Olympus Pen E-P1, Lens: Olympus OM Zuiko 135mm F/2.8 telephoto lens, exposure setting f/4.0 and ISO 200. The shutter speed of the two blended images are 1/30s and 1/125s.

We open the +1 EV overexposure image as the background layer and the -1 EV underexposure images as the upper layer in The Gimp. We then align the upper layer to be in registration(alignment) with the background layer as in the previous article. Next we add a mask to the -1 EV upper layer. The first selection on The Gimp "add layer mask" dialogue is the white mask. A white mask blocks the image from the background layer and displays the image from the connected layer. We are supposed to paint part of this mask black to reveal the mid-tone and shadow area from the background layer. Doing that takes some time and we also need to be careful with our brush strokes at the edges and boundary of the highlight area.

This time around we work smart and use a short cut method to create our mask. The -1 EV underexposed image, other than the bright area, the overall image is quite dark. So we use that image as our dark mask and paste it over the connected layer mask to create an instant masking. We do that by clicking on the small thumbnail of the -1EV image on the layer dialogue or layer palette followed by "Select All" and then "Copy". Next we click on the small white mask box next to the thumbnail of the -1 EV image on the layer dialogue of The Gimp and "paste" the image on the layer mask. We see an instant blending of the image right after the pasting and the white mask box on The Gimp layer dialogue becomes a black and white mask.

We further fine tune the 2 layers exposure blended image by editing the layer mask. We can edit the layer mask by manually painting over it for fine adjustment. That is time consuming but delivers finer control at the precise edges of the blended image. However the cut-and-paste mask looks fine so we just tweak it by using the curve adjustment to adjust the contrast of the mask. Next we Gaussian blur the layer mask with a radius of 60 pixels to smooth the transition of the blending.
Easy Exposure Blending of Western Courtyard of The Curve Shopping Mall with The GIMP
To compare apple to apple this same image we use in the previous articles is intentionally reused for this Easy Manual Exposure Blending articles. -- Camera: Olympus Pen E-P1, Lens: Olympus OM Zuiko 135mm F/2.8 telephoto lens, exposure setting f/4.0 and ISO 200. The shutter speed of the two blended images are 1/30s and 1/125s.

The image created from this 2 layers easy exposure blend method looks as good as the previous method. However with one less layer we reduced the time and errors in aligning the layers and creating layer masks. The copy and paste mask method makes it so much easier and faster to create the layer mask. It take us only 10 minutes or less to create a 2 layers exposure blend, with most of the the time actually taken up in image alignment and tweaking of the layer mask.

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