How Does One Clip, Copy Or Export An Image And Preserve The Original Quality?
I have been trying to clip an image using ArcGIS Pro (2.3). I need to send this image to a 3rd party, so it's not going to be used in my system. I am simply trying to convert an ESRI GRID format image into a smaller ESRI GRID format image. I have tried various geoprocessing tools:
- Extract by Mask
- Clip (using a polygon)
- Copy Raster (after using clip in Raster Functions)
And have used various compression settings:
- LZ77
- JPEG
- LZW
I also always let the software build pyramids using the -1 option, and have tried setting "no data" to both "0" and "256". I have not changed the projection.
None of my methods seem to work and in every case the resulting image appears coarse and no like the original at all. All I want to be able to do is capture a piece of our high-res orthophoto and preserve the original image quality in the resulting image, which sounds fairly straight forward.
Because each iteration of my workflow takes about 15 minutes this project is starting to cost me hours...even days. Surely there's a smart way to deal with this, right?
Original Image
Resulting Image
Suggestions?
Thank you
I just used #clip raster by polygon with default Environments settings on a GRID image and the clipped out put was indistinguishable from the original. In screen shot below, the area inside the yellow polygon is a clip raster output laying on top of the original raster - no visible difference.
I'd recommend trying NOT using 0 as a NoData value - that might be why you are getting those "speckles" in the dark water areas. Those look like they might be valid black 0 values within the image. Once you've done that, make sure that the #Raster Layer Appearance Stretch Type is set to None.
Good luck.
Jay:
Thanks very much for your response...most appreciated. I took a little while to respond because I wanted to try this out a few times to make sure I could replicate your results.
I tried processing this clipped imaged 3 different ways using just the default settings, but it sill produced the same grainy coarse results (as per below). This is very frustrating. I tried Clip Raster using my polygon, Copy Raster, and then Clip from Raster Functions using the Export Raster option...all with just the default settings, but nothing seems to change.
I'm wondering if there is a default setting somewhere that is overriding my process each time? I say this because no matter what settings I use the results never seem to change regardless of what compression method was selected, which to me seems odd.
Yeah - this is very puzzling.
Is your output actually a different pixel size than the input? Can't tell from the screen shots. Rt-click raster layer, Properties, Source, Raster Info:
There ARE other default Environment Settings under Analysis, Environments. Guess you could check those to make sure there is nothing weird set there, although I'd assume these would get over-ridden by whatever you set in the tool.
Have you tried doing the same operation in ArcGIS Desktop?
Jay:
Thanks a lot for your time on this...this has me double-checking my entire workflow too, which is a good exercise.
The cell size in both original and resulting images are identical (x=0.1, y=0.1), which is a good thing to check as that could have this affect if these were different. I checked the general Environment settings too and those turned out to be the same as default settings when I use the tools in ArcGIS Pro. So I'm pretty sure that there was nothing there that could be affecting my output.
I also tried my workflow 3 different ways using ArcMap (Raster Clip, Raster Export and Extract by Mask), but all 3 returned the exact same results. In one method I tried using a different compression option, but that too made no difference.
Raster Clip using ArcMap in ArcGIS 10.6.1
I had this same issue when I originally created the image from 192 TIFF images, but what ended up resolving that (for some reason) was using JPEG compression (not sure why). That has no effect here though.
Interestingly, with exception to the resolution over the water, when I zoom in to a larger scale I cannot see the coarseness anymore...it's only at the smaller scales where this becomes more obvious.
This is quite baffling. One would think that one should just be able to clip the image while maintaining the quality of the original image...I wonder what's really going on in the background when I process this image?
Original Image
I hope this can be resolved...I would hate to quit on this.
The source data specs are:
The specs on the clipped raster:
One question though...could this be a problem because my original raster image was created using JPEG compression? Just a thought.
Thanks
Jay:
Thanks again...this gives me an opportunity to explore a different angle to this problem. I will work on this today and see what happens. The latest version of the clipped images is 1 GB...it's a fraction of the original (10 cm resolution), so if I could share that somehow I would. However, I did take a peek at it using the "Zoom to Source Resolution" and it pretty well substantiates my observation on the coarseness disappearing when zoomed in. The clipped image is to the right of the red line:
This is a snapshot of what it looks like when I zoom out to 1:30,000 scale:
Thanks again.
Jay:
I have 192 original TIFF files that pieced together form our orthophoto. Each TIFF is simply named after the NW corner of a UTM coordinate, so it was fairly simple to find the right TIFF files (there are 9 of them for the area I was trying to clip). Why I cannot clip or export the raster to a new GDB is beyond me.
So what I did was create a new Mosaic using those 9 TIFF images, but instead of using an 8-bit unsigned pixel type I used a 64-bit instead, and it works perfectly. The new image is virtually indistinguishable from the original:
Now I have a format that I can share with our 3rd party...a clip would have been so much easier though.
The one thing that bothers me about Mosaics though is that periodically the Mosaic path gets corrupted, and then one has to fix that, which can be a pain as it doesn't always work.
I tried clipping this image, exporting it as a GRID file, and using that Mosaic to New Raster tool, and none of them worked (i.e. they all produced the same coarse imagery as I was experiencing before).
It looks like I will have to go with this Mosaic and hope for the best.
