I recently backup my images on Google drive. The images were bigger in size and were in GBs in size which i reduced to ~700MB (deleted few repeated images). Among size reduction methods most of us reduce the image resolution i.e. number of pixels are reduced. For example Full HD images are reduced to qHD or 720p. But i didn't reduced the number of pixels but number of colors!
This is already a reduced image of size ~900KB. I captured this image in my garden in 2016 summer using my Nubia Z9 mini phone. Its already reduced in size to load faster on website.
- ImageMagick's convert tool. This s a commandline tool which can reduce jpg size to desired size. Example: convert -define jpeg:extent=500kb nubia_bks_camera.jpg out.jpg. This will reduce original image to ~500KB without changing resolution.
- jpegoptim: this tool is same as imagemagick with desired jpg size.
- IrfanView. This is a windows only GUI software which can reduce jpg files to desired size.
I have created my own Android app which can do above size reduction and is very easy to work with. Here is the link to my app Jpg Image Size Reducer: https://play.google.com/store/apps/details?id=org.greh.imagesizereducer. A quick usage example of this app is you share your selfie which is 2MB and want to reduce size quickly without editing the image. Share it with any image app and select jpg image size reducer and reduce to whatever % or KB and then share the copy to wherever you want!. It can also reduce many files in batch. Its also an image converter and can convert non-jpg files to jpg and reduce its size.
The software above reduce number of colors which reduces size of image even more than reducing size does. However Using both methods can give very small size images. Reducing total colors to few thousand or hundreds can be noticed easily by zooming. Another method to reduce image size is to change image mode to INDEXED from RGB. Indexed mode means all colors are collected at a place/table and index/position of a color from table is used. This can reduce size. However this is not always better.