Map resizing

[Gamegasm]

I am trying to figure out how to keep the pixels from a map (https://hero339.deviantart.com/art/Sandpoint-Swallowtail-Festival-444154646) to stay the same when I am bringing up in FG.
I am using PS and I am starting by cropping the picture in half (3600x2500), then changing the style to fixed size to show how many px (50px square using the "steeple on the front of the church").
Then save for web (JPEG, Quality 50, optimized checked, 50% (to make image 1830x1275) quality: Bicubic Sharper) ~750k file size
when I bring up in FG and set grid 50px it doesn't match up to the square on the church steeple (I used that as a reference)

How can I make the scaling stay when I reduce the image size to keep 50px?
Basically I don't want that huge of a map and trying to keep my map sizes under 750kb size.

[Trenloe]

If you want to keep a certain pixel size for the FG grid (jn your example 50 pixels) you can't reduce the dimensions of the image as this will automatically reduce the pixel count per 5 foot square (or whatever dimensions you will be using for the FG grid).

The image you link to above is 1024x1399 pixels - which will give you 20.5 x 50 pixel squares wide.

If you want to keep a certain pixel size, but reduce the storage size of the image to below 750KB in size then you need to experiment primarily with the JPEG quality and colour depth (reduce to 8-bit). There'll be a point in the JPEG quality setting where the look of the image will really begin to degrade so just above that will be your lower limit. But, if you have a large image (in pixel dimensions) you may not be able to reduce it to 750KB without it beginning to look crappy - you may have to live with the image size being above 750KB to keep it good looking and 50 pixels per grid square.

[Gamegasm]

whoops sorry forgot to mention used the download link on that site to make it 3660x5000.
I guess I can just crop it down some more to keep size down and keep one full sized copy that has quality set to 1 if they decide to start chasing down the street

[Trenloe]

Ah, OK - got the full sized one.

You'll find a number of example images in this folder: https://www.dropbox.com/sh/rc5m9buybtkps62/AACwTpmwuNODDpjLbxd4332La

I used GIMP to reduce the colour depth to 8-bits per pixel (256 colours) and then exported with various quality settings from 50 down to 5.

5 is pretty poor when you zoom in, but 8 is usable (1MB in size).

[Gamegasm]

Been working on it, got to 2200x2200 with 696kb desktop looks like this now:
7135

[Trenloe]

Cool. :)

Very nice image by-the-way.

[Blacky]

I would recommend using ScriptJPG to reduce the file weight (byte size). It's better than anything Photoshop or The Gimp can do out of the box, even with manual optimization (by the way, in Photoshop save for Web, better to stay at 51% quality, at 50% and under the quality drop like a stone but the file weight not so much).

I mean, on your map there, ScriptJPG reduce the map weight from 28776KB to 4220KB with (for a rpg battlemap) very little visual quality drop. And it's still at 3660×5000.

At 50% pixel size, it's 1034KB.

Etc.