How could I split this image?

[dv8_fx]

I forgot to mention....

Choose "ALL SLICES" from the Slices pop-up....



EDIT CORRECTION....... ....sorry, my mind's somewhere else in workland.....

 

[Tom Mann]

...I don't know whether you require a bleed area but if you do, merely increase the canvas size with the required bleed. For instance, adding 300 pixels (1 inch) gives 150 pixels or half an inch on all sides.

In addition to the bleed area around the periphery of the poster (that dv8 mentioned), you might also find that extending the canvas of each 4x6 by a 1/4 inch or so in both directions to give a thin solid border/bleed (white? black? some other color?) around each 4x6 might be handy depending the exact method you are going to use to physically mount the 4x6's, especially if you are trying to achieve reasonably accurate spacing and alignment of each 4x6. If you need to do this, an easy way to automate the process is to write a short action or droplet to add it to each 4x6. These are the types of "extras" that Adobe Reader and the Rasterbator website methods mentioned above provide to save the end user work.

FWIW, personally, if I'm forced to put together a mosaic-like construction like this, I don't like to use a border of any solid color around each 4x6. This is because if you space one of your 4x6's slightly too far from the next one, the viewer sees the solid color peeking through, and since there will be a lot of places where this will happen when you are hand assembling it, it can come out looking like a bunch of thin, uneven line of varying widths running through the mosaic.

OTOH, if you try to ensure that viewers don't ever see these solid color borders by intentionally spacing the component prints a bit too close, then you are guaranteeing that the neighboring images will never be in perfect alignment - they will all be partially overlapping, and parts of the image will be missing. This can also look quite funky, LOL.

Rather, I prefer to include a true bleed area (ie, extra image area) and possibly even crop marks on each 4x6, but don't actually trim each page as printers would do. This way, small placement errors are less obvious and won't be so visible to the viewers.

Tom M

PS - I now realize that your goal really sounds like it is more in the direction of increasing your knowledge of PS and doing this job yourself, but just in case you are interested, I just double checked the prices for having a 18x24" photo poster made. At the three places that I checked, Vistaprint, Zazzle, and PosterPrintShop.com all were in the $10 - $20 range, and the only work required on your part is to upload your photo.