Getting rid of background
It is a common problem in microphotography that the illumination of the microscope field is not completely uniform.
Question: would it be thinkable to take two photos, #1 of the empty field, #2 with the object and combine them in one psd as layers and substract #1 from #2 to get rid of the background?
Masking is out of the question due to the contorted character of the object and the unavoidable loss of edge detail in touching up the mask.
I hope I did not miss the obvious answer to this in Richard's book,wich I confess to be still digesting.
Masking is the way to go...
... it's just how you create the mask.
1. Start with two layers:
-- the bottom layer is your picture #2, label this 'image'
-- top layer is picture #1, label this 'bg'
2. duplicate the image layer and move it to the top, so that the layer stack is:
3. with the 'image copy' layer selected, change the blend mode to "difference" and merge down (command/ctrl+E)
4. use the HP tools "Clear Black" and "Commit Transparency" and rename the resulting layer 'mask'
You'll find that the bg layer has now been replaced by the mask layer. To use the mask layer:
1. duplicate the image layer and move to the top.
2. group the 'image copy' layer with the mask layer (command/ctrl+G)
3. select the image layer and create a new fill layer
You'll find the background replaced by the fill layer's content.
Note this'll only work if the background you want to remove is the same in both pictures (so that the 'difference' in the RGB values is '0' and thus renders as black)
Last edited by pmarchant; 07-25-2003 at 06:17 PM.
Hmmm. Somebody's been studying their Hidden tools. Difference mode is indeed a good solution IF the lighting will be identical between shots and IF the object being introduced is not completely opaque in areas.
Nice solution Paul.
Thank you for a quick and very clear answer!
It works beautifully. one little point though: "Clear black" did'nt work but "Drop Black" did; Ctrl+E did'nt work but Ctrl+G did.
Any comments ?
Thanks for dropping in. Both ifs are met
What part of your book should I have read more attentively?
As far as the difference between drop and clear black...it sometimes depends on what you are doing, and I think either of these will work. You want to group with the mask and commit the transparency (so it is actually transparent rather than just invisible). If you aren't sure why you are doing either of these, I'd re-read those sections too.
I don't know that I said anything there...did it help?
I suspect that is still going to take some time
I recently got my hands on a copy of PS 6, so the temptation lurks to make the whole thing an action .
BUT the process uses your HPE1 tools...so the question becomes: can I just copy (or install..) them in the action directory of PS 6 ?
OR do I have to fish out the equivalent steps in PS 6 ?
OR can I access the HPE 1 action script (wich I surmise was written in PS x)and read off the PS steps ?
OR am I too ambitious ?
these are good questions.
a) Can I copy? i don't know that there is anything you can do with actions in PS6 that you need my Hidden Power for. if so, and you need to use a reference, that is ok (this would say something like Play hidden power "this action" in the action steps). Copying the sequence to a new action is a copyright violation. Re-recording, technically is not. conceptually, I leave that up to you. If it is for only your use...the restrictions are far fewer.
b) You may simply need to learn to work with tools a little more in-depth to apply some of the background I have included in the tools, but i DO NOT discourage you from taking the tools apart and learning from them. In fact, the book tells you everything the tools do...my goal was to educate the reader, and the more you learn, the better!
c) am I too ambitious? No. You have the PS6 demo, PLEASE use it to your advantage. All I ask is that you don't do like some already have and run away with my idea claiming it is yours. I can't enforce, and won't. I'd just like to have my ideas help promote my book and free tools...and those that need help will hopefully come and use them. Hopefully everyone benefits. All I want is that I get proper credit for my ideas and effort.
I hope that answers. if you need to we can set up a call to discuss.
is going to take time. As i say in the intro...10+ years (now 11) and still learning every day. If you take photography before that there are a lot more years (started when I was 9). Can I fit it all in a 300 page book? Do I expect you'll grab every nuance that is clear to me?
You'll probably have to read it a few times at least!
First it would allow to automate the elimination of the background in large series of micrographs and relieve the strain of watching my "steps"(pun intended)
Second, it would let me peek in the innards of actions and learn how they tick so that
Third, I could risk my hand at creating some, mail them to you and IF they are working well and IF you find them useful, I would be honoured to see them included in one of your future batches(does this settle the copyright infringement issue?)
Thank you for your help
Glad it worked in the end.
The difference between "clear black" and "drop black", is that clear only removes pure black, whereas drop additionally fades out the "almost pure" blacks. I suspect that your two images may have looked the same, but the underlying image data was just slightly different. In which case the difference blending won't yield pure black.
I don't know why Ctrl+E didn't work, as that is the keystroke for Layer>Merge Down which merges the currently selected layer with the layer immediately below (as long as both are visible).
I've only had Richard's book for about 3 months (and PSE2 for about 4) so I've not digested it all! I find I'm using masking a lot, and the excellent section on saturation masking demonstrates you don't have to use the lasso tool to create masks. Once you understand what the Transparent Blending HP Tools do, making masks gets easier. For example, by using a levels-corrected luminosity separation, a curve, and Transparent Grayscale I was able to create a midtones mask. With different curves I also got masks for shadows and highlights (but now HPT3 provides a quicker way to do these two).
It's also worth playing about with the blending modes. I just created black, 50% grey, and white fill layers, a black to white 0deg gradient layer, and a spectrum 90deg gradient layer. Then tried various combinations of the layers to see what (if any) effect the blending modes have.
Last edited by pmarchant; 07-26-2003 at 09:43 PM.
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