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I photograph a leaf on a blue background. The original image is 6000x4000. I want to make the background transparent. So I use the Color Range selection tool to select most of the blue background. Then I use Select and Mask to tidy up.

In particular, I need to remove some dust spots from around the leaf and select areas the Color Range selection missed. I invert the selection so that the leaf and dust spots are surrounded by marching ants. Then I use the lasso tool in subtract mode to select large areas around the outside of leaf, thus deselecting any dust and left over blue. I run the lasso tool well outside the borders of the image so that I am cleaning up right to the edge of the image. Then I save out to New Layer With Layer Mask.

The problem comes when I "Export As" that created layer+mask so that I can end up with a PNG file with transparency. The size of the image as reported in the Export As dialog is now smaller - Might be an odd number like 5829x3650. I have determined that this size reduction happens when I have used the lasso tool outside the image and essentially deselected an entire original edge. It's hard to explain.

But I think PS thinks its doing me a favor by reducing the image (and canvas) size to only the part containing the selected leaf. Changing the canvas size back to 6000x4000 will indeed export a 6000x4000 image, but then the registration of the leaf is off (it has shifted location relative to the original image). This is important, because later, I will also export the black and white mask (which remains at 6000x4000 for some reason). I need the mask for other operations, but the exported leaf must be registered with the exported mask.

So, is this normal behavior? It sure surprised me. Is there any way to prevent Select and Mask from changing the size of the image? I think this also happens if you use the selection brush and brush all along an edge. Any other ideas about how to restore the image size without shifting the location of the leaf?

Image descriptions:

First: Just about to close lasso loop selecting area to remove from selection. Note that includes the entire top border

Second: The "Export As" dialog showing that the image size has changed, and its consistent with more or less having deleted the top part of the image where the lasso tool was used

Just about to close lasso loop selecting area to remove from selection.  Note that includes the entire top border

The Export As dialog showing that the image size has changed, and its consistent with more or less having deleted the top part of the image where the lasso tool was used

  • Hi Dave, welcome. Could you add some screenshots to help make you problem easier to understand? – Luciano Dec 23 '16 at 17:14
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Select and Mask doesn't change the size of anything. When you do any sort of copy it only copies areas that have content. So there's some minor outliers you missed. In fact you can see some particles on the left of the second image. If it weren't for those it would be to the edge of the leaf.

You need to either Duplicate to a New Document using Copy Merged. Or Export using Save For Web, instead of Save Layer As.

  • But I don't really copy anything. I left the outliers at the bottom half of the image to demonstrate that that part of the image does not get cropped. But I removed outliers from the entire top half all the way to the top border, and that's the key. So upon Export As, the image has actually changed size. My work around currently is to use the lasso tool to remove the outliers all the way to the border but just keep a tiny bit of each corner unselected. In that way, PS CC 2017 doesn't crop the image or whatever it is doing. – DavePSB Dec 23 '16 at 21:17
  • @DavePSB I feel like you read the word copy then ignored the rest of my answer. Nothing in your comment leads me to believe my answer isn't the correct one for you. Either Duplicate it to a New Document first or use the Save For Web. You're using Save Layer As -- thats the issue; Layer is confined to its contents. – Ryan Dec 24 '16 at 1:26
  • You are right. I'm sorry. Indeed, if I use Flatten Image and then Export As, the export remains at full size regardless of what I do with the lasso tool. I was definitely confusing exporting layers as opposed to exporting a flattened image. I will check out Copy Merged as that sounds less destructive than Flatten Image. Makes sense now, and thank you, you answered my question. – DavePSB Dec 24 '16 at 9:07

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