[FIXED] Why '.png' files produced by ImageMagick are so much bigger than '.jpg' & '.gif' files?

Issue

I'm using ImageMagick to convert some files from one format to another. I was always under the impression that .png files were supposed to be as big/small as .jpg if not smaller, and definitely smaller than .gif.

However when I run

convert photo.jpg photo.png 

The files I'm getting out is about 6 times bigger than the original jpg.
Original jpg is a regular photo about 300x500 px, 52 kb. Output is a proper png of the same dimensions, but size is about 307 kb?

Does anyoone know what the hack is going on? Am I doing something wrong?

P.S.:

I tried both on Debian and Windows with the same results.

P.P.S.:

Also when I add resize option to this and resize to 10000 x 10000. Converting and resizing to jpg takes a few seconds, but it works, if I do the same of png, I jsut strt running out of memory altogether

P.P.P.S.: For people who keep marking this question as duplicate of PNG vs. GIF vs. JPEG vs. SVG - When best to use? . Please read carefully and understand the question. It's not a duplicate, since this question asks' about files produced programmatically with specific application (image magick). The question you marking as duplicate, is asking which image format is better to use on the web. Two DIFFERENT questions.

Solution

JPG is a lossy compression algorithm while PNG is a lossless one.

This fact alone will (in general) make JPG images smaller than PNG ones. You can tweak the compression ratios for each format, so it could also be that you're not compressing your PNG files as much as your JPG ones.

For a photographic image saving as JPG will usually produce a smaller file than PNG as there's more noise or randomness in the image for the compression to work with. Images created by graphic art tools will tend to have more hard edges and areas of solid colour which will compress better in PNG.

If you have text in your image then PNG is going to produce a better quality image as the harder edges of the characters won't be blurred like they would be if JPG is used.

GIF is smaller because it's based on an colour palette (of 256 colours) rather than the separate RGB values for each pixel (or group of pixels) in JPG and PNG.

Answered By - ChrisF

Answer Checked By - Candace Johnson (PHPFixing Volunteer)