High Resolution Bitmap Export (perhaps via slicing)

[mwenz]

Here's a modified version. The screen shot is of an exported PNG with the 4 slices selected. The slicing rectangles are colored for effect. Both colored and non-colored rectangle versions are in the same document.

The ZIP contains PNGs and a XAR file.

Take care, Mike

[mwenz]

BTW, you do not need to work with transparent slicing rectangles. Like in the XAR file I attached, after you Clip the art into the rectangles, you can select just the rectangles in the Layer gallery and then set them to transparent. I think it helps using colored rectangles and then change the fill afterwards.

[jpavel]

mwenz, thanks for taking the time to look through the files.

Indeed, when I switched page units to pixels, I saw that my rectangles were not whole pixels after all.

When PhilM wrote

It's a good idea to make sure that your tiling rectangles are a whole number of pixels wide and high in the export resolution. E.g. if you are going to export at 300dpi, make the tiling rectangles be a multiple of whole inch sizes.

I'd assumed that because I was exporting at 300dpi, if I made my slice-squares 1in, it would work; however, when I switched to pixels, I saw that the squares were 95.6pix wide. Does Xara work with pixels (or floating point fractions of pixels) internally, and then just map to other units when required? So that minute errors may be introduced when specifying a value in other units?

As in the file you sent me, when I changed all the squares to be 96pix wide, and aligned them to pixel boundaries, the image exported perfectly.

Thanks!
-Jesse

[PhilM]

Designer stores coordinates in high-resolution units called "millipoints", they are 1/72000th of an inch and they can represent inches accurately without rounding. Making a rectangle 1 inch wide and then changing to pixels should show exactly 96 pixels (because there are 96 pixels per inch).

So you probably had line widths contributing to the size of the slicing rectangles while you were constructing and sizing them. You should either remove the line width from the rectangles or turn off "Scale line widths" while you are setting them up. This will make sure the size is accurate and that they snap together properly.

Don't worry about the sizes of the slicing rectangles in screen pixels because screen pixels are not used when you export at a different resolution. Just think about whole multiples of the export resolution (whole number of inches is safe whenever you set an export resolution in "dpi" - dots per inch).

Phil

[jpavel]

Ah, quite useful to know!

It does sound likely that the initial construction of my squares was affected by the width of the lines.

Is there a way to see exactly the position and size of an object, without the sort of display rounding on the infobar that shows, in this case, 95.6 pixels as 1in (in other words, so that I would see the rectangle was only .9958 inches)? If Scale Line Widths is off, a value that I type into the W and H fields will be used as is, without accounting for the line thickness?

Thanks,
Jesse

[pauland]

It's great to see the solution to this problem here, but am I the only one seeing the irony of PhilM giving excellent assistance to solve the problem ( it's good that you chip in on this, Phil), with a manual solution that should be achievable via software? It's definitely doable - we can see that Xara can build the tiles, why can't the software just automatically do the tiling and construct the assembled bitmap as an export?

Quite a few people seem to use Xara for large scale images, is there a click-and-go possibility on the horizon, Phil?

[csehz]

How about this method, which is high-res, non-destructive of your document and avoids the anti-aliased edges:

* Create a new layer on top of all others called "Slice".
* Draw the tiling rectangles on that layer, ensuring that they are all snapped together exactly.
* Make all the rectangles on that layer have no fill and no line colour
* Now select one of them. This is tricky when they are invisible but there are various ways to do it. Either go down to outline mode temporarily to clicl on the outline or use the Tab key in the selector Tool.
* Now choose "Export...", choose PNG, choose Area to save: "Selection", choose Colour depth: "True colour", choose "maintain screen anti-aliasing", and set whatever resolution you like.
* Export and repeat for all the other rectangles on the "Slice" layer.

The resulting high-res bitmaps should fit together perfectly without any edge artefacts.

Also check out Imagemap exporting and the "Save each layer to a file of its own" option to help automate the process a bit.

One more thing: It's a good idea to make sure that your tiling rectangles are a whole number of pixels wide and high in the export resolution. E.g. if you are going to export at 300dpi, make the tiling rectangles be a multiple of whole inch sizes.

Phil

Phil thanks very much for this method