Struggling to change colour & local contrast of a crack

[Ozymandias]

Hi,

I've been struggling the whole day to change the colour of the black crack in the attached picture to red (to match my other samples) whilst fading the crack edging (paint overrun). The best I could get was to manually dodge tool the cracks to lessen the excess paint outside of the cracks but then the dodging lessens the contrast of the crack crevice too. Any advice, tool tips, on how to (1) locally contrast the cracks from the paint around its edges and (2) change the colour of the crack from black would be greatly appreciated (& perhaps help regain my sanity)



I've tried playing with overlays whilst adjusting the colour modes for the cracks, but I've not met with much success and I'm not sure if its my lack of knowledge of these features or if its just the wrong approach altogether. PS. I'm using CS2 (its what the office has...)

thanks,
Ozy

 

[Ozymandias]

also what I should have mentioned is I have to do this to quite a few pictures so am less keen on manually zooming in and handbrushing it, and would therefore prefer some cunning systematic use of modes/colours/filters. that said any help would be greatly appreciated!

 

[ALB68]

Like this? I did this by first making a new layer. Then I used a selective color adjustment layer on the black to give it more contrast. The I simply used the Image/Adjustment/Replace Color. Move the fuzziness slider until you are getting your black lines. Then take the eyedropper and select from your existing red. I did the selective color adjustment to make the red a little brighter.

 

[Ozymandias]

yeah that's a great deal better. My aim is to reduce the crack thickness more so that when zoomed out the cracks don't seem way larger than they are in reality. how did you do the above?

 

[ALB68]

Not sure you saw the edit. Just bumping it up.

 

[Tom Mann]

It would be very helpful if u could post the original of the rock at full rez.

Tom

 

[Tom Mann]

Given the OP's comment about needing to process quite a few images like this, here's an alternative approach that may allow the operation to be more automatic:

1. Start with a decent, in-focus image.




2. Duplicate that layer, desaturate the new layer; apply the "Glowing Edges" filter. You'll have to play with the various parameters of that filter to have it select the cracks in your particular starting image. Invert the result.



3. Duplicate layer 2, and apply the "Dust and Scratches" filter to remove some of the popcorn noise and make the white areas merge a bit better. Again, you'll have to play around with the settings of this filter to optimize it, but once you have good settings, they should work for similar images.



4. Make a selection out of the B&W image in #3. There are a bunch of ways to do this. With layer 3 visible, I simply went over to the "channels" palette and clicked on the RGB channel to make a luminosity mask. Add a red color fill adjustment layer and mask it with the mask you just developed. Also, I adjusted the blendIF sliders for that layer to keep some texture in the red area. The result is shown below.





It definitely isn't perfect, and you'll always be able to improve the result of any automated process by hand-painting in the mask, but maybe you can get some good-enough results out of this process without too much hand tweaking.

HTH,

Tom

 

[Tom Mann]

One can greatly improve the automated detection of cracks by heavily processing the starting image with noise reduction software. I used two passes through Neat Image to get this:



Then, using the method described in my previous post (ie, the "Glowing Edges" filter), one can turn the reduced noise version of the starting image into a nice mask. In fact, the spatial resolution is now so good that the two sides of each crack are detected separately:



Finally, one can use the resulting mask (or easy variants of it, eg, blurred slightly) to produce final images like this:



HTH,

Tom M

 

[tomross]

That first method and example is really nice Tom! Good technique.