Open Photoshop and create a new document. Set image size to 128x128 pixels @ 8 pixels per inch & change to greyscale colour mode.
Next click Filter>Add Noise
I've used a setting of 40% Gausian for this particular map, but a higher noise % will give stronger variance.
However use settings which best suit the variance map you need to create.
Next we need to double the size the document, to allow for a 50% offset to alternate rows. It's important that 'Nearest neighbour' is selected in the resample drop down list.
This is important because any other setting will cause the map to blur, which defeats the object of this method.
Now we need to change the selection box tool to 'Single Row Marquee Tool' - This will allow us to select single rows of pixels in one click. Right click the selection box tool button to open the menu.
As we doubled the resolution of the image, we need to select two rows of pixels per single row of variance. Hold SHIFT key down and click both pixel rows of each alternate variation row, working your way down the image.
Now we need to create the offset for the alternate rows we have just selected. Click Filter>Other>Offset
Enter 1 pixel for the X offset (Make sure 'Wrap round' is selected) & 0 pixels for the vertical offset.
If a different offset is required, 1/4 for example, then the image needs resizing to 4x original (512x512) then an X offset of 1 pixel would give a 1/4 running offsdet to the variance map. If this is the case jump back to step 4 and resize accordingly.
Next Resize the image to a decent scale - 2048x2048 in this example, again make sure 'Nearest neighbour' is selected in the resample drop down list, to stop any blurring of the map.
Then save the map as a .PNG file for use.
Using the textures.
If you know the required size of one block on the texture, ie if this was a paving variance map, then you can multiply up this dimension by 128, as this map has 128 x 128 blocks.
For example, a paving block dimension of 600mm x 900mm would require the following to be used in 'Real scale' UV projectors. (Maxwell & Lightwave.)
128 blocks x 600mm = 76800mm or 76.8m of real scale paving blocks
128 blocks x 900mm = 115200mm or 115.2m of real scale paving blocks.
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