White backgrounds and clean sensors

[Jim Poor]

First, let's bust a myth. Blinkies on the camera do not equate to loss of data or totally blown highlights. They may indicate some data loss or some totally blown highlights, but not usually. Of course, there is no difference on the camera between a little blinky and a lot blinky so you really can't tell without some experience.

Hot white backgrounds are sort of my thing, and I learned a lot from Zack Arias in his white seamless tutorials. Here is part one of his five part tutorial: http://www.zarias.com/white-seamless...-1-gear-space/

Now, on to today's show.

This image was one solid "blinky" on the back of the camera and looks to be pretty darn near to pure white, and at f10, the sensor looks to be clean.



Ha! Guess what.



If you really want to see the difference, view the larger image:

http://www.pbase.com/jimpoor/image/131464523/original

Run my background / sensor check action on it and the background is far from pure white and the sensor is FAR from clean! (Too much time in the dusty horse arena!)

Okay, so how to make the action. I modified the way Zack checked his BG in the tutorial by adding an adjustment layer and leaving it in place to work on the background, but Zack's way works too.

Open an image and start recording an action (if you don't know how, there are tons of ways to find out).

Duplicate the BG layer.
Add a levels adjustment layer.
Move the mid-tone slider almost all the way to the right. About 0.10 will do.
Select the layer 1 copy.
Select the dodge tool set to highlights and about 10%.

Stop recording.

Now, you can use this action to just check things out, or if you go on with the dodge tool, you can correct any underexposed areas like Zack does in his tutorial.

The time saver here is that with the adjustment layer, you don't have to keep re-doing the levels adjustment. You can work "under" it, and turn it on / off to check progress.

[Jim Poor]

Just to clarify, the dots are "sensor dust" and the wrinkles are just that - slight wrinkles in the BG.

Here's a tip. don't get hung up on sensor cleaning. The only blob I worry about is the one in the upper left corner (it will be dealt with today). The rest don't show up in any "normal" work I do, so I don't freak out about them.

[jml79]

I think that I would like to try this but being a GIMP/Linux user I am not entirely following what you are doing or what it is doing to the image. Could you break the steps down as to why and what each step does or if someone is fluent enough in both GIMP and PS maybe they could translate. I am sure with a few more details flushed out I could replicate this.

Thanks

[Jim Poor]

Sorry, I don't speak Gimp, but the step are broken down one by one when I talk about building the action.

Use whatever levels / exposure adjustment tool Gimp has to make the image darker.

[jml79]

Hmm, did some heavy PS reading and figured out where I got lost.

Add a levels adjustment layer.

Doesn't translate. Just a different way of doing things. Gimp edits the image directly instead of using adjustment layers. I just had to figure out what that was.

Move the mid-tone slider almost all the way to the right. About 0.10 will do.

I have no idea how to replicate this one but I'll give it a shot.

Thanks again for the tutorial.