sliced image too big when exporting

I tried resizing the original image so the exported slices are smaller but the quality was bad, tried resizing the exported images but same result. At 72dpi the size is perfect but rubbish resolution.

By @katinkaing

That would have worked if they were saved out after resetting the ppi, without any resampling.

You said the tiles ended up 83*108 cm each. If what it actually said was 83.33 x 108.34 cm, and we assume 72 ppi (the default assumed for images with no ppi metadata), then:

83.33 x 108.34 cm at 72 ppi actually equals 20 x 26 cm at 300 ppi. It’s the same number of pixels (2362 x 3071).

So then, if I was trying to fix this, one way would be to create a Photoshop action that does this:

1. Open a tile.

2. Choose Image > Image Size.

3. Make sure Resample is deselected (very important).

4. Change Resolution to 300 ppi. It should now read 20 x 26 cm at 300 ppi.

5. Click OK.

6. Choose File > Save a Copy, choose a file format, save.

Run the above action on all other tiles.

If you watch the pixel Dimensions line in the demo below, it does not change during this edit. That shows that the image content does not change, no detail is being lost, because it’s the same number of pixels before and after (because Resample was disabled). The only thing that changes is how dense the pixels should be assumed to be, which is what ppi resolution metadata is all about.

The reason to use Save a Copy in step 6 is so that the resolution metadata is embedded. Most other export methods in Photoshop do not preserve resolution metadata.

What file type are saving the slices as?

In Save for Web it seems if one sets the Metadata to All, JPEG saves the resolution, but PNG-24 does not.

This is with Photoshop 2024 (ps ver 25.4) running on macOS Ventura 13.6.4

@katinkaing 

As mentioned by @D Fosse – the issue is that the very old code used for Save for Web (Legacy) has an 8192 px limit as the input size, before it scales down the original oversized image (check the % value, it will no longer be 100%).

So you can crop the original to less than 8192 px on the longest edge, then Export > Save for Web (Legacy), then undo the crop and redo the crop on the other side and then repeat the export etc...

In addition to the input size issue, Save for Web (Legacy) will strip the resolution/print size metadata, so even if the slice size is correct in pixels, it will likely be incorrect in physical size. If saving to JPEG, I have a script that can reset the missing resolution metadata to 300ppi:

Photoshop version:

Bridge version:

Otherwise, some scripts can save slices to files or layers without using Save for Web, so don't have the size limitation:

There is no size change. The file is just pixels, and image pixels have no physical size, they are just data points. The image has no physical size.

The physical print size is set by assigning a pixels per inch-number (ppi). That number can be anything you want, and the pixels in the file will print at the size defined by the ppi number. "Pixels per inch" means exactly what it says. But the pixels are the same, and you can change the ppi number without changing a single pixel in the file.

Pixels per inch is a formula for translating pixels into physical sizes. It's a simple equation: ppi = pixels in the file/print size in inches.

Save For Web strips the ppi number from the file. It is irrelevant for web/screen which is what Save For Web is intended for.

Most applications will assign a default ppi number when opening the file. A ppi number, any ppi number, can be required for other reasons such as calculating font sizes. Photoshop assigns 72 by default.

Nothing in the file changes.

Note that Save For Web has one limitation: it will not accept files bigger than 8192 pixels long side. Anything bigger will be downsampled.