Sampling Toned Images with The GIMP
Ever seen a great toned B&W image and wished you could tone your images that way? Wondering how difficult it is to do your own sepia/platinum/silver/cyanotype/duotones/tritones/quadtones/<insert your favorite> toning in the digital darkroom?
At Photoshop for Photographers (click in the left column on “Black and White” and then on “Copy a Tone”), Thomas Niemann describes an excellent technique for “mimicking” tonings found in existing images and applying them to your own images using Curves . Of course you can reproduce this procedure (with only slight variations) in the GIMP, but fortunately for GIMP users, there is a much, much easier way!
The GIMP has a great filter called Sample Colorize. This versatile filter allows you to “rip” (sample) the colors used in an image and apply them to a grayscale image. It is particularly effective on extracting tonings from images where there is only a single tone corresponding to a particular luminosity level. In other words, most toned B&W images, but also most duotones, tritones, quadtones, etc.
In this tutorial I’ll show you how to use this filter to tone your B&W images with a wide variety of tonings and to rip your own tonings.
|Load image to be toned.|
|If desired, convert it to B&W.If you don’t, the image will be converted anyway, so if you are picky about how this is done do it yourself.
Just make sure the image is back in RGB mode when you are done (Image/Mode/RGB).
In this case, I decomposed the image and used the Red channel.
|Load the second image that has the desired toning.You can load more than one if you want a selection to choose from.
If you need some samples, try these.
|Move your cursor focus back to the image to be toned and run the Sample Colorize filter (Filters/Colors/Map/Sample Colorize).In the sample side options, choose the appropriate toning image in the drop down box. You probably want to keep the “Smooth Samplecolors” checkbox checked and the “Use subcolors” unchecked. In the destination side options, you probably want to keep the “Hold Intensity” checked. See the discussion in the Tips section below for some information on these.
Click “Get Sample Colors” to get the sample colors into a the destination preview.
If you want to adjust the luminosity (brightness or darkness) of the destination image then uncheck the “Original Intensity” option and adjust the In Level sliders accordingly (if you try to run an ordinary Levels command after the toning you may shift the toning color in unexpected ways). If Original Intensity is checked, then adjusting the In Level sliders just changes the distribution of sample colors without affecting luminosity. Play with this option a bit and you’ll see what I mean.
After adjusting settings to your liking, click “Apply” to tone the actual image. Sit back and drink some coffee. On my Athlon 1800+/1.5GB the filter took 78 seconds to run on a 3000×2000 pixel image.
Discussion of Sample Colorize filter options
The “Use Subcolors” option only comes into play if you are mapping a sample image that has more than one color for the same luminosity level. In this case the filter has to decide which color gets mapped to the same value point in the destination. This option determines how the colors are sampled to affect the corresponding destination values. If “Use Subcolors” is off, then the dominant color is used (the one with the most pixels with that value); if the option is checked, then the colors are sampled in a weighted fashion.
For example, suppose you are trying to sample a color photograph that for a particular value in the range 0-255, say 101, there are four distinct colors with that overall value, each in different amounts. Suppose that the percentages for this value break down as: 50% of the pixels of that value are the first color, 30% of them are the 2nd color, 18% of are the 3rd and 2% of a fourth. Now our sample gradients that we are mapping to have one column for each value, from 0 to 255, and each column is 100 pixels high. So for this value, if “Use Subcolors” is checked, the 101th column will have 50 pixels of the first color, 30 pixels of the 2nd, 18 of the 3rd and 2 of the last. If the option is not checked, all of the pixels in column 101 will be of the color that has the 50% share.
If you are sampling a typical toned B&W image this is not an issue, and the setting doesn’t really matter, since the majority of the pixels in any column would end up being the predominant color in that level. However, I would recommend unchecking the option in this case to avoid contaminating the sample with stray pixels. On the other hand, if your intent is to capture the toning of a photograph that does make use of multiple colors within the same brightness level, you’ll want to select this option. Please realize, however, that the sampling will only be approximate: e.g. if you tried to recolor a desaturated version of the original sampled image with your new gradient sample it would not be able to reproduce the original exactly, and in fact you may be lucky to even get close to it. I’ve found that it can often do a decent job though. Visit the samples collection to see an example of what I am talking about.
The “Smooth Samplecolors” option allows the filter to interpolate colors for missing values in the sample image, resulting in smoother gradations of toning in the destination. Posterization might result if you don’t check this option. There may be situations in which you do not want to check this option (odd, non-linear effect tonings come to mind), but I think it is a good idea in most cases to select it.
According to the GIMP Users Manual, if the Hold Intensity option is unchecked then colorization is accomplished by mapping the color in a semi-transparent layer over the image, rather than by “true colorization”. I am not sure what they mean by this. I have experimented a bit with this option and it doesn’t seem to make much difference to the result. If someone can clarify this option for me please drop me a note.
See the manual for a discussion of other filter options/controls not discussed here.
- The Sample Colorize filter also allows you to just work on a selection instead of the whole image. This is handy if you want to tint different parts of the image separately or use different tonings.
- Another very similar toning approach uses gradients. Open the Gradients selection dialog and pick an interesting gradient. Then run Filters/Colors/Map/Gradient Map. You can create new gradients using the Gradient Editor.You can also choose gradients as the source in the Sample Colorize filter. This must work nearly identically to Gradient Map except that you have the extra options for subsampling, etc.
The real benefit to GIMP users in Niemann’s tutorial is his collection of classic tones (visit Photoshop for Photographers and click on “Black and White” and then “Classic Tones”). These are sampled here, along with some others. You can download a particular tone by shift-clicking on it’s gradient; save it and use it to tone your own images. Note that the displayed gradient is not the same as the sample gradient! i.e. don’t right-click to save the gradient with the text on it, shift-click to save the link target!
You may be interested in my more comprehensive collection of tonings.
Creating Your Own Samples
If you make (or find) a toned image that you’d like to capture a sample from for toning future images, it’s a snap to do it.
|Download this grayscale gradient and open it in the GIMP.|
|Now load your image that has the desired toning.If the image has a border, caption/text, etc. that is not toned, be sure to crop that part off so as not to contaminate the tone sample.
For best results, try to find a toned image that has a complete range of tones, from very dark to very light.
|In the grayscale gradient, run the Sample Colorize filter (Filters/Colors/Map/Sample Colorize). Choose the image you want to copy the tone from in the sample side.If the image to be sampled has more than one color per luminosity value (e.g. a “color” photograph as opposed to a toned B&W photograph), then be sure to check the “Use Subcolors” option.
Click “Get Sample Colors”. When that has completed, click “Apply”; the grayscale gradient should take on the toning of the sample image.
Now save your gradient as a new toning sample, preferably as a PNG or TIFF.
If you find a great toning image somewhere or come up with one a great tone and you’d like to see it added to the toning samples collection, please send me the gradient as prepared above. If you have a particular name in mind for the sample send it along in the email message body.
p.s. I am also looking for traditionally (wet darkroom) toned images to use in verifying the authenticity of these “classic” tonings. If you have such an image, I would appreciate it if you could send me a small digitized copy of the image; it need not be any bigger than 300-400 pixels in any dimension (just big enough to contain the full range of color values in the image). Alternatively, if you see one on the web, please point it out. I am currently looking for good examples of any interesting historical tonings.