Manual Exposure Blending in the Gimp

07 October 2008

I've been watching people post HDR images for months, and I recently stumbled upon Meet the Gimp: Episode 25 which discusses exposure blending. The hard part was defining a clean mask for blending the images.

It's not the crazy tone-mapping stuff, but this technique allows for some relatively natural looking changes.

Blending can be done by copying the layer with the most contrast (or darkness), and applying a Threshold to it, and adjusting the slider to get a clean edge. Then invert, and copy that black-and-white threshold image to be a mask for your top layer. A little hand painting and Gaussian blur finishes up the mask, and it should look pretty decent.

My sunflower image is an example of using this technique with 3 exposures pulled from one RAW image. The threshold and blur helped immensely to help define the edge between plants and sky with minimal halos.

Wall-E is another example, but I used the technique to blend different saturations for emphasis of the subject, and deemphasis of the background.

I've recently noticed a few Exposure and Blending Mask options in Gimp's Photo filters, but I've not had a chance to see what they do -- maybe it's the more automatic way to do some of this stuff.


My New Photo Workflow

07 October 2008

I've been tuning my workflow a bit -- the process of pulling images from the camera, processing, editing, and getting them posted. I still do everything on Linux.

Downloading Images

To start, gthumb started out very helpful -- the first time I plugged in the Nikon D40, it popped right up and offered to pull the images for me. I had been using that for months, but eventually, the whole thumbnailing processing got too slow on particularly large downloads. I didn't need to view the thumbs first, I just need the images, so I wrote my own script to do about the same thing, only faster:

#!/bin/sh

cd ~/photos
DATE=$(date +%Y-%m-%d-%H-%M-%S)
mkdir $DATE
cd $DATE
LAST=$(gphoto2 -L | tail -1 | cut -d' ' -f1 | sed 's/#//')
gphoto2 --get-raw-data 2-$LAST --filename %f.%C
ONDISK_COUNT=$(ls | wc -l)
EXPECTED_COUNT=$(($LAST - 1))
echo $EXPECTED_COUNT $ONDISK_COUNT 
if [ "$ONDISK_COUNT" -eq "$EXPECTED_COUNT" ]; then
    gphoto2 --delete-file 2-$LAST --recurse
fi

This downloads the images to a timestamped directory, and clears the camera for me.

RAW Processing

I open the directory of images in Rawstudio, and quickly rate the images. I mostly just mark the keepers as '1' and occasionally rate higher for images I want to get processing first. I delete anything unrated (discarding 90% of my RAW images).

I make a second pass over the keepers to look for potential deletes, then I get to work processing each image in Rawstudio. I've not figured out an appropriate way to batch my images through RAW processing yet, so I do each individually. I straighten, crop, adjust contrast, exposure, and saturation. After all the images are done, I batch export the JPEGs to another directory.

Rawstudio 1.1 added the ability to automatically copy the RAW metadata to the JPEG EXIF data, so that saves me an entire script which I would often forget to run.

Final Editing

I fire up Gimp on each image, and often apply a GREYCstoration to smooth image noise and almost always apply a small-radius (0.9) unsharp mask (at about 1.10 or so).

I found this great guide to using the tunable parameters of GREYCstoration. Read this, and you'll figure out how it's affecting your image. I play mostly with the Strength, Anisotropy (amount of structure in the image), and sometimes the Noise Scale and Iterations.

I occasionally get into cloning and healing in Gimp.

Uploading

I shuffle the finished images into a few directories by trips or themes, and upload each directory to my Gallery 2 install using the (From Server) upload. Then I push 1 or 2 of the best images up to Flickr via the basic uploader on the website.

Archiving

The RAWs remaining RAWS go to the NAS for backup, and I'm usually done with my processing within a few hours of plugging in the camera.

On a gear note, I am starting to think about purchasing a Wacom tablet for editing -- a basic tablet is relatively cheap, and could make some work a lot easier. It's been a while since I've purchased anything.


Gimp Tips from Meet the Gimp

10 July 2008

I've been sitting on a little email note to myself since October! It's just my hot tips I collected from the early episodes of Meet the Gimp. Finally, I'm going to put them here, so I can find them again, and I can delete that email.

Keys:

Faking some simple adjustment layers:


Tip for Sharpening Images

01 February 2007

Photodoto has a quick photo sharpening tip that I'm finding really useful in Gimp and surprisingly simple.

I now take these steps (optionally):

  1. Curves to correct exposure and color.
  2. Crop with fixed ratio (2:3 or 3:2) select.
  3. Selective Gaussian Blur to smooth ISO noise.
  4. Duplicate the layer.
  5. Unsharp Mask the new layer.
  6. Add a black (transparent) mask to the sharpened layer.
  7. Use a large brush, and paint white (opacity) onto the mask in just the lines I really want sharpened, such as the face or hands, or generally , the subject of the photo.
  8. Flatten.
  9. Save.

Am I missing any other tricks? Not that I'm saying I need to spend even more time post-processing images. Somehow, though, I am caught up on stills and video right now.


All the Posts

October 2008

July 2008

February 2007

October 2006

December 2005