Image Analyzer examples

Help index

Fourier transformation

I have been asked about saving the result of the Fourier transform and editing it in another program. It is simply not possible to save the result of a Fourier transform to a standard image file. A Fourier transform produces complex numbers whereas e.g. BMP files can only contain ordinary integer numbers in the range [0; 255]. If you want to edit the Fourier image and be able to do an inverse transform, you have to either use the editing function in Image Analyzer or edit the MAP file you get when saving the Fourier transform. In Image Analyzer you can use the eraser tool or make a selection and hit Ctrl-Delete to remove frequency components, or you can use the Frequency domain filter option in the Filters menu.

PNG versus GIF and JPEG

Why is there no GIF under File format options so that I can make transparent GIFs etc.?
Most people only use GIF for single images because of ignorance. There is really no reason to use the old GIF format anymore. Use PNG instead! All modern browsers and graphics programs support PNG, it has better compression (produces smaller files) and it supports more color formats (e.g. 24 bit). The 256 x 256 grayscale image in the top of this page takes up 63 kb as GIF and only 41 kb as PNG. This means 30% disk space saved and 30% less download time.

If using the lossy version of PNG the size reduction is even greater. With a quality setting of -7 the PNG file size is 21 kb - only one third of the GIF file and without significant visual quality loss. Lossy JPEG can produce even smaller files, and is in most cases better for photographic images. But JPEG does not support transparency, and is not very good at compressing images with sharp edges like diagrams and screenshots.
Note that the lossy PNG compression is not as effective with 256 color palette images as with grayscale and 24 bit images.

Auto color correction

Auto color correction adjusts black/white point, gamma and saturation. This will improve the contrast and enhance details in the image. Black/white point and gamma are adjusted in the same way as when you press the Auto button in Color mapper. The adjustment is based on an analysis of the image. By making a selection before clicking Auto color correction you can tell the program to only analyze that part of the image. You would probably want to do that when correcting a picture with e.g. a black background.



Red eye removal

Make a selection around the red part and click Red eye removal (Alt-E). The selection does not have to be very accurate, but making it too large might result in loss of color around the eye.

Saturation and Vibrance

Saturation and Vibrance is almost the same thing in Image Analyzer, except that vibrance will do less correction of colors that are already highly saturated to avoid color clipping.


Help index       Last updated 2017-01-15 by Michael Vinther       [Send e-mail]