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Home - General / All posts - M9 handling 2 byte color brightness in images, 255 max vs 65535
736 post(s)
#20-Mar-23 18:23


I am importing (or linking) an image, in TIF format, georeferenced by someone else. In M9 the incoming raster image renders as a completely black rectangle, On reading the manual and searching the Internet for channels, RGB, and brightness, I understand that channel values in M9 can be from 0 to 255 (256 steps in brightness). In the M9 manual examples, the maximum channel values I see are 255.

After importing the TIF image and inspecting the Style panel, I see the channel values are 65535. If in the Style pane I change these channel values to 255, the formerly black rectangle renders correctly in black and white similar to the original paper map.

Testing the georeferenced image in ER Viewer and in QGIS, the image immediately renders properly upon importing (render as a map in black and white, the same as the original paper map).

On my reading, I understand RGB channel brightness can be represented in one byte (max value 255) or two bytes (max value 65535). So the maximum brightness doesn't change, only there is finer gradation. It seems M9 can handle already channel values > 255, the image becomes darker and darker as I enter values > 255.

Note. The TIF image came with additional files, .ovr, .aux, and .xml.

In a future version could M9 handle channel brightness represented by one byte or two bytes values? Unless there is a reason not too, I will submit a feature request. So the request is not to handle finer gradation of brightness but to simplify importing images that use two bytes for channel brightness.

channel brightness.jpg


503 post(s)
#20-Mar-23 18:50

Try adjusting the range by Ctrl-clicking on the three channels and right-click choosing autocontrast at 2.0 std. The choice of Full Range may also help to illustrate the details of the channels.

736 post(s)
#20-Mar-23 19:06

Thanks oeulong. Wow, I would have never found that as the right click options only are available on CTRL-Click. I will experiment some more with the different autocontrast ranges and full range. Anyways, that did the trick.

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