The DiffALL Blog
Practical guides on image and video quality metrics, compression, and media comparison workflows.
How to Compare a 4K Video to a 1080p Copy
Did the downscale lose anything beyond resolution? What a comparison of two resolutions can tell you, what it cannot, and which check answers the rest.
Audio ComparisonHow to Compare Only Part of a Long Recording or Video
When the part you care about is in the middle, compare from there. How to pick a start point, and why a short clip against a long file scores low.
Image ComparisonHow to Compare Two Photos Taken From Slightly Different Angles
Two phone photos of the same thing never line up pixel for pixel. How a comparison can align them first, what it can and cannot correct, and how to read the result.
Audio ComparisonHow to Compare Two Recordings That Start at Different Times
Half a second of extra silence at the top can make two identical recordings look completely different. How automatic alignment works, and where it stops.
Audio ComparisonCan You Compare Two WhatsApp Voice Messages to See If It's the Same Person?
Voice notes are short, compressed and recorded on phones. What that does to a same-speaker check, what we measured, and how to give it the best chance.
Image ComparisonHow to Find Colour Changes Between Two Images
A recoloured button with the same brightness can fool a greyscale comparison completely. How colour is compared, and what the score tells you.
Audio ComparisonHow to Null Test Two Audio Files (and Hear Exactly What Changed)
Flip one file's polarity, line them up, and what is left is the difference. Why a null test by hand fails on one sample of offset, and how to get a clean one.
Image QualityWhat Is Chroma Subsampling (4:2:0), and Why Does My Text Look Smudged?
JPEG and most video store colour at a quarter of the detail of brightness. Invisible in a photo, obvious on red text and logos. What 4:2:0 means and how to avoid it.
Audio ComparisonCan a Voice Comparison Tell If Someone Is Disguising Their Voice?
Phone lines and faster speech barely move a voiceprint. A voice changer moves it a lot. What a speaker comparison can and cannot tell you about a changed voice.
Image QualityDoes My Photo Show Where It Was Taken? Checking for GPS Location
Phone photos often carry the exact GPS position they were taken at. How to tell if yours does, when it survives sharing, and how to remove it first.
Image QualityHEIC vs JPEG: What Actually Changes When You Convert an iPhone Photo
iPhones save photos as HEIC. Why the files are smaller, why so many apps cannot open them, and how to convert to JPEG without losing visible quality.
Video QualityHow to Tell If a Video Is Too Shaky — and Why a Pan Isn't Shake
Shake is not movement. It is a change of movement from one frame to the next — which is why a smooth pan is fine and a handheld close-up is not.