Is there a way to write a GeoTiff file with Color and Alpha Channel Data using geotiffwrite?

21 次查看（过去 30 天）
Sonoma Rich
Sonoma Rich 2023-4-3
评论： Taylor Shropshire 2024-12-17，21:08
Is there a way to write a GeoTiff file with Color and Alpha Channel Data using geotiffwrite? I tried defining a TiffTag for "ExtraSamples" as shown below, but I got an warning message. The image (img) is a n x m x 4 RGB image where the 4 index on dimension 3 is the alpha channel.
geotiffwrite('img.tif', img, R, 'TiffTags', struct('ExtraSamples', Tiff.ExtraSamples.Unspecified))
Warning Message:
Warning: Sum of Photometric color channels and ExtraSamples does not match the value specified in SamplesPerPixel.
Writing with this configuration will error in a future release. To correct the configuration, define the non-color channels as ExtraSamples.
I get an error if I try defining the "SamplesPerPixel" TiffTag as 4. I don't know how to define the non-color channels as ExtraSamples using geotiffwrite.
I used the following example for Tiff objects to try to create the alpha channel data:
Write Tiff Image with Color and Alpha Channel Data

请先登录，再回答此问题。

回答（1 个）

Shubham
Shubham 2023-5-31
Hi Sonoma,
Yes, it is possible to write a GeoTiff file with color and alpha channel data using geotiffwrite function in MATLAB. However, you need to correctly define the "ExtraSamples" TiffTag in order to do so.
From the error and warning messages you received, it seems like the "ExtraSamples" TiffTag was not defined correctly. Instead of defining it as "Unspecified", you can define the non-color channels as "ExtraSamples". For example, you can modify the "TiffTags" struct as follows:
TiffTags.Photometric = Tiff.Photometric.RGB;
TiffTags.BitsPerSample = 8;
TiffTags.SamplesPerPixel = 4;
TiffTags.ExtraSamples = Tiff.ExtraSamples.UnassociatedAlpha;
This sets the "Photometric" tag to RGB, "BitsPerSample" to 8 (assuming your image has 8-bit color depth), "SamplesPerPixel" to 4 (indicating that there are 4 color channels), and "ExtraSamples" to "UnassociatedAlpha" (indicating that the extra channel is an alpha channel that is not associated with any specific color).
Then, you can pass this "TiffTags" struct to the geotiffwrite function like this:
geotiffwrite('img.tif', img, R, 'TiffTags', TiffTags);
This should allow you to write a GeoTiff file with color and alpha channel data using geotiffwrite function in MATLAB.
  3 个评论
显示 1更早的评论
Taylor Shropshire
Taylor Shropshire 2024-12-17，16:54
I also had the same issue and have not found a solution. Shubham could you provide more information?
Its possible to modify a tiff object (T) as you describe. This can then be used to create a tiff image write(T,rgb_with_alpha). Although I don't think there is a way to convert the tiff object to a geotiff.
setTag(T,'BitsPerSample',8);
setTag(T,'SamplesPerPixel',4);
setTag(T,'ExtraSamples',Tiff.ExtraSamples.UnassociatedAlpha);
Creating a TiffTags Structure does gives the error described by Sonoma Rich
TiffTags.Photometric = Tiff.Photometric.RGB;
TiffTags.BitsPerSample = 8;
TiffTags.SamplesPerPixel = 4;
TiffTags.ExtraSamples = Tiff.ExtraSamples.UnassociatedAlpha;
geotiffwrite('file.tif', img, R, 'TiffTags', TiffTags);
Thanks for any support.
Taylor Shropshire
Taylor Shropshire 2024-12-17，21:08
I stumbled upon a very easy solution... geotiffwrite will create transparency for all grid cells that have RGB=[NaN NaN NaN]. I used QGIS to load the file. Hope this helps someone else.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Other Formats 的更多信息

标签

产品


版本

R2020b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by