How to use PosiTweak
First, download and install PosiTweak from the Downloads section. It's a slow and clunky old thing written as a quick hack several years ago. My apologies, but it does the job.
Before running PosiTweak, the negative you want to process must have its colours inverted to turn it into a positive. PosiTweak does not currently do this, but most photo editors will. If you do not have suitable software, I highly recommend the freeware program IrfanView from www.irfanview.com. The Negative command is on its Image menu. The image must be saved in BMP format, as this is the only import/export filter built into PosiTweak. IrfanView and many other programs will convert between BMP and other formats.
Tip
If you want to use JPEG compression, only convert the file to JPEG format after you have done all your editing. While working on it, use a lossless compression system such as TIFF set to LZW compression in the options. Repeated loading and re-saving of a JPEG gradually degrades its quality.
Here is part of a scanned negative transformed to a positive:
The problem is that negatives have a strong red/orange bias. When the colours are inverted this transforms into a blue cast. I will give you a few point-and-click instructions to correct this with PosiTweak but it is well worth learning the background theory. Click here to read it.
Run PosiTweak. Drag the BMP file out of Explorer and drop it on to the 'Drop BMP here' spot on the upper left. Two points: (1) It is best to store the BMP in a folder whose path is not too long. A long path will occupy all of the title bar and you will not be able to see important information. (2) I didn't implement scrolling so you will only see part of a large image. This should not be a problem as your settings will work on hidden parts of the image too.
Click on the blackest part of the image you can find and note the Red, Green and Blue values shown in the title bar. Sample many points and pick the lowest values you can find. Enter them into the Black Point boxes.
Repeat for white areas and enter the values in the White Point boxes.
Click the Process button and the correction will be made.
If you are unhappy with the result, press Reload and adjust the settings. When finished, press the Save button to save the processed image.
No transaprency adaptor for your scanner? Click here to find out how to make one.
