Help with images please

[AlexBell]

Most of the ebooks I prepare for the MobileRead library are a hundred or so years old, and in some of them the associated images have a grey or sepia background so that they do not show well on a monochrome ebook reading device.

I know virtually nothing about images or image properties - I don't even know enough to know where to start googling. Can anyone point me to information on how to lighten the background and increase the contrast so as to make the images appear better?

I have on my computer PMView (which I've used since my OS/2 days), GIMP 2, IrfanView, and Paint.NET. But except perhaps for PMView I haven't the sightest idea how to use any of them or where to begin.

[Toxaris]

Both with GIMP and Paint.Net you can run the contrast filter. Put it on 25 and apply. For most pictures that is sufficient.

[AlexBell]

Originally Posted by Toxaris

Both with GIMP and Paint.Net you can run the contrast filter. Put it on 25 and apply. For most pictures that is sufficient.

Thanks, Toxaris, I'll give Paint.Net a try.

[dwig]

Simply increasing contrast can work, but often creates problems with detail loss. In the case the OP describes the undesirable loss would be in the shadows; the desirable loss being the highlights gray/sepia tones.

A better control with which to make the adjustment is either Levels or Curves (Photoshop terms, most apps use similar). These can alter the highlights without a complimentary change in the shadows.

While I'm primarily a PS users (20+ years), I have found that PhotoScape (freeware) is quite usable for basic changes. It has a Luminance Curve (click the "Bright, Color" button in the Editor to get the menu) control that is similar to PS's Curves and handles this type of edit easily. Dragging the upper right control on the curve allows you to adjust the highlight clipping (remove the gray/sepia background tone) and you can click and drag on the curve to bend it for further adjustment, again like PS's control.

[AlexBell]

Thanks, dwig, I've just added PS to my list of graphics programs.

[SBT]

Hmm... isn't this a good idea for a wiki page?
I've previously suggested using imagemagick. Though excellent if you need to batch-process dozens of files, it's rather demanding to master.

Gimp isn't the most user-friendly either, but you get decent results with it:

1. Load image
2. Rotate as necessary [From toolbox]
3. Crop as necessary [Select rectangle tool in toolbox, then Image->crop to selection]
4. Choose Tools->Color->desaturate to get B&W
5. Choose Tools->Color->levels:
6. Tweak black and white levels by:
   • selecting the black or white eyedropper tools and click on a region of the image that should be black/white.
   • and/or Use the sliders beneath the histogram.
   • and/or click on 'Edit as curves' to get even more control.

I also like to use Filters->Unsharp to enhance the image.
There's also an excellent wavelet denoising plugin that can be installed which works wonders on grainy images.

[Jellby]

When i want to make sure the background is really white, after converting to grayscale (Image -> Mode -> Grayscale):

1. I create a new black layer on top of the image.
2. I set the layer mode to blacken (not darken): everything that's not pure white in the bottom layer appears black.
3. I set the black layer opacity to ~50%
4. I apply the Levels command to the bottom layer (move the white level until most background is white, without losing detail in the picture).
5. I delete (paint white) all remaining speckles in the background (making sure I paint on the bottom layer, not on the black layer).
6. I delete (or hide) the black layer.

[AlexBell]

Originally Posted by SBT

Hmm... isn't this a good idea for a wiki page?

Yes!

Thanks for all the suggestions - I'm still trying but can't get the hang of it.

For graphics I really need instructions with one syllable words suitable for a five year old.