An easy way to remove stray pixels in Photoshop
No matter how thick my skin gets I still hate getting images rejected by stock agencies. Sometimes though, it’s all for a good reason and something great comes out of the whole learning experience.
Yesterday was one of those days.
I’ve been trying to get a whole lot of model isolated on white images accepted at all the microstock sites this week. They were shot in studio with four lights. The background was over-exposed by enough stops to make it look white for just about anyone using the images for anything.
The trouble is that microstock inspectors must be playing the levels adjustment in Photoshop when they review images. There is almost always some residual sensor information in the “white” areas which is made visible by pulling the levels slider to the right.
While nobody I’ve ever met would actually do this under normal printing or publishing of an image, many of the stock houses will reject such images because they are not really “isolated” on white since there is a colour value of the “white” pixels.
This is an odd position to take, since many traditional agencies take the opposite view and don’t want maximum white or maximum black pixels and will reject you if you’ve gone too far with an isolation!
The microstock agencies, however, want their whites to be totally white. That’s #ffffff in hex.
If you pull the levels slider across in Photoshop and the area that used to be white gets a lot of grey spots – those are stray pixels and you will probably get rejected for them.
It’s a bit of a pest to get rid of stray pixels, but I might have found a much easier way to get rid of the pesky things last night.
Here is a quick run down on how to remove stray pixels without messing with your image colour balance, having to use the pen tool or clip your histogram:
1. Open the image in question.
2. Duplicate the layer.
3. With the top layer selected: Image > Adjustments > Levels
4. Pull the left slider across until you can see the stray pixels. Click on OK.
5. With the top layer still selected: Image > Adjustments > Levels
6. Underneath the Options button on the right, select the “White point” eye dropper.
7. Select different grey areas until the background is mostly white.
8. Click on OK. Your subject is now mostly black and your background is mostly white.
9. Select the magic wand tool with a tolerance of 1 or 2. Click on the white background area.
10. Select > Inverse
11. In the main tools pallet (the one with the Pen tool, text tool, crop tool etc) select the button “Edit in Quick Mask Mode”. It’s a rectangle with a circle in it second from the bottom of the pallet in CS 3.
12. Your “white” background will now go red or pink.
13. By using the paint brush, you will now be able to “select” any additional stray pixels by “painting” over them turning them red or pink. They white point eyedropper should have got you pretty close, but there will probably be some additional stray pixels to include. If you are half-competent at studio isolations your job should be easy. If much of your subject is included in the pink area, you have over-exposed your main subject and your isolation job is going to be much harder. Try isolate by creating a path with the pen tool!
14. Select the bottom “Background” layer.
15. Switch the top layer off by clicking on the little eye next to the layer.
16. Make sure that you still have the background or bottom layer selected after turning off the top layer. You should see your image main subject with a pink “white area” for a background.
17. Click the same rectangle and circle button which now ready “Edit in standard mode”.
18. Select > Inverse
19. Select > Modify > Feather (select a value of 2)
20. Hit Delete
Stray pixels should now be gone. You can test this by flattening the image and playing with the levels slider again. If the main subject goes darker and no stray pixels appear in the form of dark splodges in the background, all is good.
Note that with this process your colour did not shift, nor did the histogram go all clipped and wonky like it does if you try and remove stray pixels with the white point eyedropper by itself.
If you have a better or faster way – please let me know!
This article was originally published on my personal blog here.
Photo credits: Alistair Cotton.
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