PNG vs JPG question.

[casterle]

I was reading an article about sizing images for Facebook and ran across the following "JPG is generally used for images with blended tones, like photos, and GIF and PNG are better for images of flat tones like logos, text and graphics."

I've never heard this assertion before and can't imagine why it would be true, but I'm not an expert. What say ye?

[carl123]

True

[PixelPest]

You might want to use PNG over JPG for decals/overlays etc because it supports alpha channel.

[gdenby]

Some comments. Rake w. grains of salt,

.GIF is a really old format, and can only offer 256 colors. Gradients must be dithered, and edge blending is likewise ragged. So simple forms w. a small number of colors are well suited for .gif. The format is 8-bit, and so tends to be small by contemporary standards.

.PNG was developed to replace .gif, but  accommodates up to 64-bit color depth. In images w. few colors, the .png routine can produce files smaller than .gif. But for images w. greater bit depth the files can become much larger. While ,png will ignore any colors not present, any of the million that are there will be recorded. The format us considered lossless. Add to that the space for transparency, and metadata, and the file size balloons. 

Also, at one time, the amount of computation necessary for the encoding was noticable. 

,JPG is considered lossy, although when the quality is set to 100%, it creates files of about the same size as .png. As compression increases, the routines average areas of color, and use methods that keep the image looking smooth to the eye. Lots of colors, and smooth smears for color gradations. Only at high compression that the artifacts become obvious. The artifacts will be there even for simple forms, so a highly compressed .jpg well not be so good for a geometric shape.