Gimp Tutorial: Light Effects with Edge Detect, Contrast and Blur

[annariel]

This tutorial focuses on making areas of lighting in your picture more pronounced and, you know, glowy. However the same techniques can be used for highlighting things, especially text, so I mention that at the end.

Disclaimer: Unfortunately there are several versions of the GIMP and they are all slightly different. I'm fairly sure everything I talk about works in all versions of the GIMP, but you may have to hunt a bit for the menu option. It's also worth noting that I learned most of this stuff by reading photoshop tutorials. The ideas are very similar and can usually be transferred between the two programs.

Edge Detect and Blur

The first technique I tried out for accentuating areas of lighting in icons was using edge detect and blur. It must be said that this can cause strange ghosting effects which you will see in several of my icons so it needs to be used with caution and I nearly always make heavy use of mask layers when I'm doing this.

So, as with so many techniques. You start with a base image and make a copy of the image in a new layer. Then you want to use the "Edge Detect" Filter on the layer.



I usually select "Edge" from that menu which then gives you several options such as "Sobel" and "Prewitt Compass". There's a nice preview window so you can see which one seems to be doing most of what you want.



Then set the layer to Screen mode (although, given my last tutorial, Dodge mode will probably generate a nice effect too).



You can immediately see the ghosting effect I was talking about in the above image. However playing with the layer opacity (in this case dialling it right down) nevertheless succeeds in accentuating the highlights on Abby's face.



As I said above I would normally, at this point, play around with masking out some of the layer and increasing the opacity to accentuate those highlights I particularly wanted to showcase.

Then you can also use various blur filters on this layer for a more "glowy" effect. I generally use Gaussian blur since that let's you control how blurred it gets.



I nearly always end up setting the blur amount to 2 or 1.




You can also sometimes use the Motion Blur from the Blur menu to good effect. The only irritating thing is deciding where you want the centre of your blur to be. I normally end up hovering the mouse over the original image and then reading off the X, Y coordinates from the bottom left hand corner. For some reason you can't do this in the preview window. In this case I decided I wanted the origin of the blur to be just below Abby's chin, which turned out to be 11, 90.



You can then use the slides below the window to fiddle with how much blurring there is and you can see the effect in the preview window.




Makes her look like she has a moustache, but you get the general idea.

Brightness/Contrast and Blur

I've since discovered you can get similar, and I think better, effects by messing around with Brightness and Contrast and then blurring.

So to start again, this time selecting Brightness-Contrast for the new layer:



This is what the top layer looks like with with both the brightness and contrast turned up high.



Then set to Screen mode (although again Dodge might produce nice effects here too).



Gaussian blur:



Motion blur:

Highlighting Text

Lastly I've found similar techniques work well when highlighting text. I often have a problem, when adding text to an image, that some part of it doesn't show up well because of the colour of some part of the background. Case in point is the A in ABBY below. NB. There are other ways to deal with this problem as well, this is just one solution.



So I duplicate the text layer and make the lower layer into a contrasting color - in this case it needs to be a light colour, but I've done the same trick with a dark colour under a light coloured text. I'm using Color Range Mapping for this.




(You change the colour of the Destination colour (or indeed any of them) by clicking on the relevant box of colour in that dialogue). Even just doing this gives you a faint outline around the letters, although I'm not sure why that should be. But a little bit of Gaussian blur on the lower layer is enough to give a nice edge effect and highlight the word:



You can also use a Motion blur to create effects here. In this case you need to scale the text layer to the size of the image first (otherwise your blur will get cut off at the edge of the text box):

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Comments

[reggietate.livejournal.com]

Interesting tutorial. Definitely handy tips about highlight text - I often get the problem of one or more letters not showing well against the background.

[lsellersfic.livejournal.com]

Seeing text is a horrible problem, I find. Almost any interesting image is going to have light and dark areas which make choosing a text colour really hard. I nearly always find I end up doing some fiddling somewhere to make sure it's legible.

[reggietate.livejournal.com]

And when your image is only100x100 there isn't much room for manoeuvre, is there? One of the fun things about icon-making is how ingenious it forces you to be at times.

[fififolle]

Ooh, that's very useful. Not done much of that before :)
Thanks!

[lsellersfic.livejournal.com]

I reckon there must be lots of stuff like this - you know standard ways for getting specific effects. I stumbled across lots of the light stuff because I was interested in trying to replicate some of the effects crazypandabear gets - but I bet there's lots of similar things out there which I just don't know about.

[gabcd86.livejournal.com]

Yay, it worked! Used the text highlighting thing to make text stand out against a black-n-white photo. :D