Image dimensions, resolution & file size ..

[dec]

i am confused. there is something i obviously do not know/understand about image files

i do not understand why files can have same size image and resolution, but different file sizes, or different variations of that issue

i have attached some examples

it makes me really worried that i don't understand what is going on and have been culling the wrong files

kindest

[cday]

I do not understand why files can have same size image and resolution, but different file sizes, or different variations of that issue.

An image consists of a matrix of pixels, each pixel having a colour value, most commonly expressed by RGB (Red, Green, Blue) intensities. For example, pure red has RGB pixel values of 255, 0, 0.

An image can be saved in different file formats, for example JPEG, PNG, TIFF or in many other less-common formats. The size of the resulting file depends on the format used, and often also on the particular format saving options used, for example which of several available compression options is selected.

The saving process may be lossless, when the image displayed when the file is opened in an image viewer is an exact copy of the original image, or lossy, when the image displayed when the file is opened in an image viewer may differ slightly from the original image saved. The practical advantage of lossy compression can be that images can be saved as much smaller files, with little or no perceptible difference in quality when they are displayed. In practice that is often an acceptable, or for large image collections a very useful, trade-off.

The quality required when an image file is opened depends on how the image will be used: whether as a photo on a webpage that will only be viewed quickly, or maybe as an image containing fine detail such as thin lines and text that may be viewed closely.

[XnTriq]

• Wikipedia
  • Image quality
  • Peak signal-to-noise ratio (PSNR)
  • Generation loss
  • Lenna → TinEye
• Softpedia
  • GIPSA-lab: PSNR
  • RGBchannel: PhotoDefiner PSNR Calculator
• XnView forum: Image Compare - add 'find difference' feature
• Kornel: How to compare images fairly
• Stack Exchange: Two EXACTLY the same .jpg images with one image more than twice the file size of the other - Why?
• Stack Overflow: Can we programmatically compare different images of same resolutions?
• Adobe: Compare image files