hpr-knowledge-base/hpr_transcripts/hpr3460.txt

Episode: 3460
Title: HPR3460: Dodge and Burn
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3460/hpr3460.mp3
Transcribed: 2025-10-24 23:52:56

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This is Hacker Public Radio Episode 3464 Friday, the 5th of November 2021.
Today's show is entitled Dodge and Burn and is part of the series Gimp It is the 230th show of Auka
and is about 18 minutes long and carries a clean flag. The summary is, we continue our look at
the layer modes in Gimp With Dodge and Burn. This episode of HBR is brought to you by
An Honest Host.com. Get 15% discount on all shared hosting with the offer code HBR15.
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Hello, this is Auka for Hacker Public Radio and back for another
exciting episode in our Gimp series and I'm going to just take a moment to remind you again
that at the time of the recording I am using Gimp 2.10.24 on a Kubuntu Linux 20.04 LTS machine.
There may be small differences if you're using a different version of Gimp or what have you.
I think particularly different versions of Gimp would matter more than
which particular operating system. Today's topic is going to be Dodge and Burn.
Now these are concepts you find in a lot of graphics programs and the names are not
to my mind all that intuitive. Dodge means to lighten, burn means to darken.
Now they exist as a tool in the paint tool section called Dodge Slash Burn with a keyboard
shortcut of Shift plus D. They show up as modes available for other paint tools. You select a paint
tool then look to the properties area just under the tools area and you will see mode as the first
option. By default the tools open in normal mode but you can select Dodge or Burn. In fact the
modes we have looked at for layers are frequently available as tool modes as well. The differences
being first of all layer modes apply the effect to the entire layer whereas tool modes can be
applied to specific areas within the image by using the tool. Secondly layer modes involve the
interaction of two layers whereas tool modes can be applied to one layer by itself. I haven't
always pointed that out as specifically as I might have in the layer mode discussions but
it's worth keeping in mind and I just pointed it out here. Now Dodge and Burn are useful tools. You
will find in many graphics programs and deserve a more in depth look. Now I'm going to cover both
as layer modes but also the Dodge and Burn tool. You will find them very handy and use them a lot
if you get into graphics. They are frequent tools used in photo retouching which is of course a
major reason for why I got into Gimp and where I will ultimately take this series.
So first let's get into the tool part of this. This seems like a good opportunity to do kind of an
in depth look at tool properties or tool options. Now Gimp uses the terminology tool options.
Other programs for the same kind of thing use the term properties. For instance LibreOffice uses
the terminology of properties for a lot of this stuff and either way we're talking about the same
thing. Many of them are the same for all of the paint tools including Dodge, Slash, Burn but
some are specific. Now to get a closer look click on the tab on top of the tool options window
and drag to unlock it. Now I'm assuming that you have locked all of your various windows down
into a single window view. Something we talked about way back at the beginning of this series
but you know maybe you've already got everything a separate windows floating around up to you.
But I think to really dig into the tool options it can help to pull it out a little bit and expand it.
And just like most windows you just pull on the edges to expand it to a comfortable viewing size.
Now if you've undocked this and enclosed Gimp when you reopen Gimp again you may not see your
tool options. But if you just go to the windows menu and then to dockable dialogues and select
tool options as what you want to open. You know this and this works for all of the dockable
dialogues such as layers, the layers window and stuff like that. Anyway starting at the top you
have the title bar that says tool options pretty standard. Then there is the open button for the
window. Now this also serves as a handy tab for docking or undocking the window.
Now if you click the drop down here you will see the same list of modes as you would see for the
layer modes. The difference again is that layer modes apply the effect to the entire layer
whereas the modes on a paint tool are applied to specific areas by how you use the tool.
Next to the mode drop down is a button to switch groups of modes.
Now the default group is all of the new modes in Gimp 2.10, 37 of them.
But if you want the modes from an earlier version of Gimp you can switch to the legacy modes.
I'm sticking to the default for the stuff I'm doing here.
I don't really see the value in going back to the legacy modes but some people may see things
differently. Then under that you have opacity. Now by default this is set at 100%.
In other words you draw something on an image with one of the paint tools it will cover
that part of the image. But there are areas like with photo retouching you sometimes want to apply
an effect with reduced opacity. And so you can control that effect here. And you can paint something and
you know if you have undue levels you can always undo, go back and redo it with a lower level
opacity. What have you? Then under that is brush. This is where you select the brush you want to use.
Now one of the critical decisions here is whether you want to use a brush with a hard edge
or a soft or fuzzy edge. Now this is controlled by the hardness setting which ranges from 0.25
to 1.0 in increments of 0.25. You have 0.25, 0.5, 0.75, and 1.0.
If you click the button you can switch the brushes around here too.
Size. You control this with the slider by typing in a new number or you can hold down the control
key while you're using the mouse wheel. Now I find the ladder tends to be most convenient because
I can get the size right with the brush on the canvas. Otherwise you're constantly going back and forth
making an adjustment and okay it's not still not quite right. So you know getting used to using
the mouse wheel is I think handy. Aspect ratio. Now by default the brush is probably going to be
circular but you can make it more of an oval with this setting and switch which way the oval
points and things like that. Then spacing. It's an interesting one. You can think of what paint tools do
as like a series of stamps on the image. You can do a single stamp by clicking on the image
but when you click and drag it is a series of stamps. Normally space so close together that you
don't even notice that they're separate but you can increase the spacing and get a series of
separated stamps. Now when you're getting to know all of these tool options what I would suggest
doing is simply open up GIMP, create a blank image, you know maybe a 1920 by 1080 pure white
and then start doing some of this stuff and see what it does. Now this isn't everything on the
tool options but we haven't spent a lot of time on that so far so I thought it was worth a
little more in-depth look and it seemed like a good place for it. If you want more and see as
much as you can about it go to the GIMP 2.10 documentation link in the show notes and you can get
all the deets as the kids say these days. Now to the Dodge Burn tool this is another paint tool
but what it does is to lighten Dodge or darken Burn the colors in your image. The key setting
to look for here is that you can set it to only affect a certain range of brightness in the image
from shadows to midtones to highlights. So if you had an image where the shadows were very dark
and you wanted to bring them out a bit more you could use the Dodge setting and shadows to do this
without affecting other parts of the image. Now in photo retouching sometimes you'll get an
image where the shadows are really dark but the parts that are in the sun are very bright. You don't
want to make parts that are bright even brighter so setting it for shadows means if your mouse slips
a little bit you're probably not going to do terrible damage to the image.
So I did an example. I opened up the landscape image that we had used previously when we were
doing our layer masks tutorial because that's a lot of shadows. Now next thing working non-destructively
we've mentioned it before but I'm going to keep mentioning it because it's an important thing.
Working non-destructively the very first thing I always do is I duplicate the layer
and then I work on the duplicate. Now that way if at some point I realize I've horribly messed it up
yeah throw away the duplicate and just start over create another duplicate until I get it the way I
want it. Now in this particular case I set my opacity on the tool to 35 my size to 30 and dodged
some of the shadows in the image and you can see how that worked on my image and it's a very subtle
effect really. Some of the darkest shadows are a little bit lighter than they were before.
Now but you don't think about doing stuff like this is most of the time you don't want it to be
obvious that you've made any changes. Now I said I had to set for shadows. I actually did a little bit
in a brighter area in the upper right and you can't tell that I did it and that's why that setting
matters. Now burn does the opposite it darkens but it has the same three options for shadows, mid-tones
and highlights. So this time I went back to the toy image because that has a lot of bright stuff.
Working non-destructively I start by duplicating the layer and applying my edits
to the duplicate. So I set the opacity to 50 but kept the size at 30.
Now I applied the burn first to the wizard's hat and to the stand for the crystal ball
and I could see a difference but it was really subtle. Then I went to the upper right of the image
which was near to being white and just did a little patch of it there with the burn tool and
you can see it went from white to a kind of a mid-tone gray. The lighter the area is on the image
the more you will see the effect here. Now that was using the dodge and burn tool. What about the
layer modes? Now the dodge layer mode like all layer modes requires two layers to work and this
is not commutative. The order really matters again. So dodge lightens using a formula that says the
resulting image will be found by first computing 256 times the R, the G and the B values for
the lower layer. Then computing 255 minus the R, the G and the B values of the upper layer.
And adding one to that and then divide the upper layer numbers into the lower layer numbers.
That's a really complicated formula here. So what we want to remember is that each pixel in the
lower layer is multiplied by 256 then divided by the inverse of the pixel in the upper layer plus one.
I don't think it's something you would do often but the resulting image is definitely lighter but
kind of strange looking in the particular example that I did with my dog and my toy.
Now burn uses a slightly different formula and that is it takes the inverse of the lower image.
So in other words 255 minus the R, the G, the B. That inverse is multiplied by 256 then divided by
the upper layer plus one values and then those the resulting the result of that division is then
inverted by subtracting from 255. In any event the net effect is to darken the image and you can
see some examples. Now the basic idea of these techniques is to solve a problem you often encounter
in photography which is that detail can be lost in two opposite ways. In some photos the shadows
are so dark that you can't really see much detail. In other photos the exposure may have blown out
the detail with too much brightness. Now the Dodge tool can help bring back some of the shadow details
while the burn tool can bring back detail from overexposed or excessively bright images.
You often see stuff like this in you know outdoor landscape photography because some
places are in full sun and right next to them might be something that's completely shaded.
So they're very useful in photo retouching you should get comfortable using them.
I think though you would use the Dodge and the burn tool a lot more often than you'd use the layer
modes. As the documentation says with respect to burn you know these are these are basically
techniques that came from photography and they were darkroom techniques.
And that starts at least that makes the burn part a little more intuitive to understand.
But burning is a technique used in a dark room to increase the exposure in particular areas of
the image. This brings out details in the highlights. When used for this purpose burn may work
best on grayscale images and with a painting tool rather than as a layer mode. So this is
what the GIMP documentation itself says. So Dodge would be just the result of the opposite
technique to that. Instead of increasing the exposure in a particular area you'd reduce the
exposure in a particular area. So good advice anyway use the tools not rather than the layer modes.
Now I think that's enough of this and next what I want to do is I want to take a look at the
darken layer modes. So this is a hookah for hacker public radio signing off and encouraging you
as always to support free software. Bye bye.
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