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

JPEG compression

[denissmith]

First, yes you can use GIMP and Photoshop to improve your images. Second, the problem you are noticing can't easily be fixed in either program. The pixellation you see is most likely a result of jpeg compression. Even jpeg fine can cause this. JPEG is lossy compression and it tries to optimize an image for shrinking. Many of the subtle shades in the sky were simply tossed out by the compressor. Use TIFF or RAW, as these do not use lossy compression. The files are much larger, but they don't use lossy routines (LZW is lossless compression, and RAW doesn't compress at all.). To try to fix the problem in Photoshop (GIMP will have similar abilities, but I don't use it so I can't instruct you) you need a good mask of the sky. Zoom in to 100% on an area of the sky ( so you have 1 pixel for each screen pixel). Use Filter | Blur | Gaussian blur and interactively blur the sky to get a smooth effect. Don't worry that it looks fake at this stage. Second use Filter | Noise | Add Noise. Take gaussian from the radio buttons at the bottom of the interactive tab that comes up. Move to a boundary of the mask so you can see the sky and the unblurred areas of the photo. Adjust the noise rate to approximate the noise in the original areas. This time it will look a little sharp, try for size approximation. Now choose Filter | Blur | Gaussian Blur again and this time select a very low number .3 or .4 pixels... adjust it to match back to the look of the original image. You will have to play around with this several times to get it right for your image - and believe me every image is different. AND NEVER USE JPEG. Save as Tiff, which is a general standard. Jpeg is for web use, it really ruins images.