Is it possible to make converted files darker than original

[mrjacoby1]

Is there some contrast setting or other way to make PDF files that I output darker? The incoming CAL files are very light and hard to read. Is there some setting I can play with to make the type darker? Thanks.

[cday]

The best solution is probably to use a 'Levels' adjustment and to experiment with the settings of the sliders for the black and white points -- a levels adjustment can be very effective.

Image > Adjust > Levels... or just hit 'L' on the keyboard for the keyboard shortcut.

Check the 'Apply to image' checkbox to see the adjustments you make full-size.

In XnViewMP the Levels interface also has a third slider to adjust gamma to further optimise the results.

There are also brightness and contrast adjustments as in any image editor.

[XnTriq]

Alternatives (especially useful for batch processing):

• Image » Map
  • Automatic levels (Ctrl+Alt+L)
  • Automatic contrast (Ctrl+Alt+O)
  • Normalize

Normalization is commonly used to improve the contrast in an image without distorting relative graylevel intensities too significantly.

[mrjacoby1]

Thanks for the suggestions, but they don't seem to work on my .CAL files. When I first go into Image>Adjust>Levels (this is in regular XnView, NOT MP), all the options are greyed out. By first clicking on Image>True Colors or Image>32 bit, THEN the "Adjust>Levels" options become available.
However, when I go into the "Levels" menu, I can't make the changes apply to the original CAL file. The "Black point" gets set to 207 and the "White point" 255 by default. By default, the "Preview" pane is also open, and the image looks substantially darker (and nicer) in that "Preview" pane. But the changes do not get applied to my original file. The "Apply to Image" box is checked by default, yet nothing happens to my original file. Even un-checking and then re-checking the "Apply to image" box has no effect on my file.
It's like it doesn't want to work on CAL files.
Any suggestions?

[mrjacoby1]

Also, I just tried the "Image>Map" suggestions. Nothing changed. Clicking on "Automatic Levels", "Automatic Contrast", and "Normalize" did NOTHING to my image.

Is there something I need to do BEFOREHAND to my CAL file so that these adjustments can be made?

[cday]

Thanks for the suggestions, but they don't seem to work on my .CAL files.

Your .CAL files were engineering drawings and likely to be black and white images with 1-bit per pixel: that would I think invalidate all the suggestions above. You can confirm the bit depth by looking in the status bar at the bottom of the screen, or using Edit > Properties.

If the images are black and white, I suspect that the lightness you're experiencing is due to the large pixel dimensions of the images, with fine lines not displaying well on your screen, which almost certainly has a much lower resolution. You could check that by zooming well in and seeing if details in the image are then well defined.

If both the above are confirmed, you will probably need to think about how the images are to be used in practice, either zooming well in when needed, using a higher resolution and probably larger screen, or by printing the files. It might be possible to resample the images to thicken details, but I wouldn't expect that to be a good solution, although you could try.

[mrjacoby1]

To your first point: Yes, 1 bit per pixel. When zooming in, the letters are very well defined.

[cday]

To your first point: Yes, 1 bit per pixel. When zooming in, the letters are very well defined.

Given that the pixels are already pure black, I don't think any of the previously mentioned enhancement methods will improve the images.

Well, you have the options listed above depending on how you actually need to use the images: you could simply zoom well in when needed, obtain a better monitor such as the recently released but expensive '4K' monitors with around twice the number of pixels (without checking), you could possibly print the images, or just possibly resample them successfully but remembering that you would be changing an engineering drawing slightly...

Another possibility might be to crop out areas of the image of interest and save them as more-viewable images.

Edit:

On checking '4K' monitors have around twice the number of pixels in both width and height, so total number of pixels is four times that of a standard widescreen monitor. Better, but possibly still not good enough for easy viewing...

[XnTriq]

Thanks for the suggestions, but they don't seem to work on my .CAL files.

Since I wasn't familiar with this file format and because I didn't have any samples, I failed to realize that CALS images are always binary (black & white).

Let's give it another try:

1. Image » True Colour
2. Filter » Effects... » Misc. » Minimum (Filter size: 3x3)
3. Image » Convert to Binary » Binary (No Dither)