Using The GIMP (or Photoshop) to Improve Photos?

Nom du Keyboard asks: "Is it possible to use The GIMP (or Photoshop) to improve my digital photos? I have a mid-range 7.1MP Olympus camera capable of shooting in Raw mode. When I inspected a section of clear blue sky on a bright, sunny day (which I've long believed to be relatively good reference of uniform color and brightness) I was surprised (disappointed, since I expect digital perfection) at the variance in adjacent pixels. It's also a quick way to identify any bad pixels. Surprisingly, actual photos from this camera look pretty good despite this variance so far. Moving on from that point it led me to wonder that, if you shot a uniform white surface, perhaps blurred as much as possible to avoid any imperfections in the surface itself, could a correction (adjustment) layer be created in GIMP or Photoshop exactly tuned to your camera that fixed the variations in your CCD sensor and improved the image quality in the process. Any thoughts?"

Comments

Learn about photography

[linuxbert]

What you describe is normal, and your question exhibits a lack of understanding about white ballence.
essentially, if your white is right, then all the other colors will be as well. your camera has several settings to compinsate for various light types (Tungsten, Flourescent, Daylight)Yours is probably set to AWB (Auto) which is easy - as the camera will figure it out pretty well and a Custom - which you can configure based on the lighting by shooting a grey card - which is a card that is 15% grey (Or there abouts) that the camera can then use to figure out what true white is.

The variation in pixels can also be the result of the ISO setting you are using. 100 has the least noise, but also requires longer exposures. higher settings react faster, but have more noise (400,800,1600) This is a tradeoff between desigered exposure and ambiant light.

I would suggest reading Strobist for more on lighting. There are also several other sites dedicated to post processing images, that you may find helpfull. it also might be worth looking at the various pool discucssion groups on Fliker.

-Peter

Re:Learn about photography

[Frobnicator]

You are right that light balance and natural noise are both very important.

Take for example the camera-assistant production slates (those little boards you see movie makers use with the clapper on top). They do a lot more than just showing the script location and film location, but they also have little black and white (and gray) lines on the clapper. Those are amazing tools that are deceptively simple. The clapper makes a sharp noise that lets you sync and balance the audio, digital boards will record the sync for individual film frames, and the lines provide for image calibration.

The black, gray, and white boards allow you to balance the brightness in post production exactly the way the original post was looking for.

Most boards also have calibrated colors to help balance those, as well.

Shooting slate is a very important step in good photography, both for stills and motion pictures.

And to the posters suggesting trying to eliminate all natural noise in photos, you don't really understand what you are talking about. Your eye expects noise in the real world.

Photos need natural noise, they look unnatural or cartoonish without it. Traditional photographs are full of noise because the silver halide gelatin and other chemicals are not perfectly uniform. The chemicals naturally clump up and form noise. (This property makes it easy to identify tampered photos since the natural noise is different between two areas.) Even digital photos get noise when you print them or display them on your screen. If your camera automatically smoothed out all the noise, the image would look like a cartoon or a naively ray-traced image.

As far as using image editing apps such as the GIMP or Photoshop, yes they are able to do a great job with digital images but they are limited by the knowledge and skill of the human using them.

Noise ninja

[Illusion]

See Noise Ninja for well-known commercial software that does this. There's apparently now also a Linux version.

While playing with it a while ago, I found that JPGs compress something like 25-33% better after you remove the CCD noise. Improving the image quality while making the images take less space seems like a nice combination. :)

This seems like it would be great to get in the hands of more people as a free software app or plugin, but I'm not aware of any.

-- Aaron

Good idea, but use black instead of white.

[NereusRen]

Using the sky or a white piece of paper may be interesting, but it probably won't give you anything you can use to calibrate the rest of your photos.

A better bet for isolating the noise your camera generates is to take completely black photos, using the lens cap and some extra covering (and a dark room) to make sure absolutely no light hits the sensors. This will let you make raw images of the "dark noise" and "bias noise" that your camera generates, and subtract those images from your real photos before doing any other processing.

Details of this method can be found here: http://photo.net/learn/dark_noise/.

Yes Exactly! Only Backwards....

[DonnarsHmr]

You're almost right. The method you're using is called Dark Frame Subtraction. The idea is that you photography the non-random noise inherent in the sensor and then take that out of the captured images. To do this, you make an image that is completely black (i.e. body cap on the front of the camera and viewfinder cover on the back) at the same temperature conditions and for the same length of shutter speed as the image you are trying to fix. Then you add that as a layer in photoshop, subtract it from the real image, and the non-random noise disappears.

However, it is MUCH more likely that the noise you are complaining about is random thermal noise, which is not treatable via Dark Frame Subtraction. Because it's, well, random noise, it'll be different in every shot. There are several photoshop plugins that can address this issue. In my opinion, the most effective and easiest to use of them is Noise Ninja.

Something similar

[ceoyoyo]

Something similar is done in astrophotography. There are two kinds of fields you can remove from your images. A dark frame (taken with the lens cap on) is subtracted to remove things like pattern noise, hot pixels and amp glow that appears in images. A flat frame is then used to remove multiplicative effects, like vignetting and dust spots. Acquiring a flat frame can be tricky. One of the best ways is to use a translucent lens cap and a fairly bright light that provides a fairly uniform illumination.

However, the effects (unless there's something seriously wrong with your camera) are really only noticeable for long exposures.

Yes

[Ankh]

First, the biggest improvement you are likely to see in the Gimp is if you go to Colour->Layers (in older versions of the Gimp it's Layers->Colours->Levels) and click Auto. For pictures that should contain some black and some white this will usually make a noticeable improvement.

Second, yes, Canon (for example) includes (Windows only, proprietary, secret, closed-source) software to compensate: you shoot a 25% grey surface. You can also use this inside the camera itself: there it will use the data for white balance correction.

In practice, though, it's fairly hard to do this yourself. One difficulty is that the amount and position of colour aberrationswill probably vary depending on the lens you use, or, with a fixed lens, the amount of zoom and the aperture size. I know I found that when my Casio developed some dark spots.

There are some programs that are used with hugin, the panorama stitching UI, that help with some lens corrections; it might be you could ask those people. However, a lot of the variation you are seeing is likely to be digital noise. Try taking 3 shots usinga tripod and timer or remote, and comparing them.