When I want scale down an image to a particular number of pixels, I use a little spreadsheet I wrote.  It is cumbersome, I have to copy the existing image dimensions into the spreadsheet, then read the output pixel dimensions and transfer that back to the image/scale dialog. Then let photoshop scale the image and save it under a new name.

I would like to figure out how to tell photoshop to create a downscaled image with a given number of pixels, for example 10,000,000 if I need a 10 megapixel image to post. I cannot just enter a fixed dimension in the height and width boxes because all my images are a variety of shapes, so each one needs a different setting.  Then I could automate the thing pretty easily to do a whole raft of images at once.

Do not know how to do this, either by some windows automation, or photoshop special trick. Do you know how?
thank you

What?  Use the PS image scale function to resize an image.

But he wants to do it as a batch function with different size images if I understand correctly.  So I believe he wants multiple images of different sizes to "automatically" be brought up to one "global" size with a batch function.

Write an action in photoshop.  Batch processing can be started from within Bridge using the photoshop batch.

Patrick.

I have a PS script somewhere on my blog you could use.

You can type in a w or h and it will show number of pixels.

In the days when Alamy required images to be upsized to 48MB uncompressed, there was a script that would do this automatically for you - it's gone now, but I still have a copy.

It has a variable set to 48 which is then converted to an absolute pixel count and does the appropriate conversion.  Not exactly what you're asking for perhaps, but I should think if you can do a little scripting you could easily convert it for your purpose.

I've put a copy here http://www.bullersofbuchan.me.uk/istockphoto/stuff/Alamy%20Resize.zip if you want to try it.

Sean's iStock resizing script should also be easily adaptable to do the sort of thing you want - it's the same principle as I recall, but has a pull-down menu to select specific sizes to suit iStock's XXXL, XXL, XL, L and M sizes.

He has it here http://digitalplanetdesign.com/index.php?page=istocktools

Quote from: Gannet77 on August 27, 2011, 13:46

In the days when Alamy required images to be upsized to 48MB uncompressed, there was a script that would do this automatically for you - it's gone now, but I still have a copy.

It has a variable set to 48 which is then converted to an absolute pixel count and does the appropriate conversion.  Not exactly what you're asking for perhaps, but I should think if you can do a little scripting you could easily convert it for your purpose.

I've put a copy here http://www.bullersofbuchan.me.uk/istockphoto/stuff/Alamy%20Resize.zip if you want to try it.

Okay worked out that what Photoshop calls "pixel dimensions" of 71.5 correspond to a total number of 25000000 pixels (5000X5000 pixel square image) which is the maximum size for a raster illustration on SS. So for my use I just changed the 48 to 71.5 in the script and it now does exactly what I wanted. Thanks!

Now can anyone explain what "pixel dimensions" in the PS "Image Size" pop up menu means? It sounds like it should be the result of height X width but it clearly isn't.

Hi. Yes, I just figured that out.  There is two factors in it, the use of 1024 x 1024 rather than 1000 x 1000 for the term 1 Meg. And the use of 3 bytes per pixel. When you peer into that script that was kindly provided, the author multiplies his desired size (TargetMb) by 1,024, by 1,024, then divides by 3.  (In memory, 24 bit images use three bytes of storage per pixel). And his term was Mb not MP.

So if you look at an image size, then do the same calculations, you will get the number that Photoshop rather mysteriously describes as pixel dimensions. They are describing memory use not image size.

For my use of the script, I just put my target size straight away into, 25 megapixel is 25000000, ditched the divide by 3 and set the new dimensions to  these factors:

target = 25000000;
(...get existing height and width..)
var aspectRatio=width/height;
var newHeight=Math.sqrt(target/aspectRatio);
var newWidth=newHeight*aspectRatio;

and this produces the desired image dimensions. (For worriers, these are in floating point figures, when you chop them to ints, then the overall
image size is alittle shy of what you want, so you have to jack around somewhat.

Huge thanks to Gannett, I am solving my file creation problems readily now.

You're welcome...  though acknowledgment is really due to Steve Smith at www.paw-print.com, who wrote the script originally.