I won’t be able to advise you on the code side of things, but for general image resizing we have a tool that can help you - the Online Image Resizer. It can help you change your images to be the same size - however this option may not be ideal for you as you would have to do it manually and one by one.
Another option for you to explore would be to go directly to the developer of the Impulse theme, and I had a look and found some contact options on their website here. They would be able to look into this even from the coding perspective as they know their theme’s code best.
Lastly, you could also look into this with a Shopify Expert. Shopify Experts are people who work externally to Shopify and charge their rates based on the work that they do. They can also look into code related questions.
I also wanted to ask you about your business - what kind of products are you selling? I might be able to advise something else based on that also.
If you have any other questions, please feel free to let me know.
I have Impulse Theme as well. I don’t have the option to change the product image size from square to 4:3. Does anyone know why this would be and how can I change it?
Thank you for the image; however, my Impulse theme is not showing the different grid image size options. Do you know why it wouldn not be showing up in my customize shop area?