Image size control when creating mosaics in Arc

[Yaneev]

Hi, question about the ESRI Mosaic Process:

I have a folder of about 40 small uncompressed tif files, totaling 6 to 7 gb. . When I try to use mosaic tools like "Mosaic to New Raster" the output raster is over 55gb. I'm wondering what is going on here that the product of the mosaic are about 10x the size of all the uncompressed mosaics put together, and what I can do process-wise so that the created mosaic represents the size of the files going into it. Ultimately, I'd like to compress the mosaic into an ecw or jp2, but I need to understand why Arc expands the file size 10x during the mosaic process. 

Any advice is appreciated. Thanks so much.

[james-noble]

Hi @Yaneev, are you processing the new raster into the same file type as the input, and have you compared the raster properties of both the input and output raster? As an example, Mosaic to New Raster allows you to control the pixel type and cell size, which could have a big impact on the output size.

Ref: Mosaic To New Raster (Data Management)—ArcGIS Pro | Documentation

[YaneevGolombek]

Thanks for the response James. A lot had to do with the size of the overall footprint, when I removed some of the outlying rasters, the uncompressed size shrank exponentially. A little confusing since I thought NoData values take up no space, but perhaps they do. Thanks again!