What is the difference between bmp & jpg? After editing a photo, my program saved it as a bmp file. I copied it and resaved it as a jpg. The bmp file is 4 times as big; yet they both look and print the same. Why??

-- harlow blodgett (blodgett_harlow@marconidata.com), February 03, 2000

Answers

The .jpg file is compressed. JPEG compression is a lossy compression, if you are going to do alot of editing and save the file multiple times save it as some other format. Every time you save a jpeg it throws away a little more data, this is how they get so small. I use LZW compressed tiff format for images that I am going to edit.

-- Don (deldon@hotmail.com), February 03, 2000.

BMP and JPG are two different file formats. Jpg is compressed meaning it throws away information (the information which is deemed to be "unumportant") and thus takes less room to store. The designers of the jpg format were good and so even though files are compressed as much as 1/10 or 1/20 their original size, the lost information is usually undetectable to the average viewer. Compression of more than 1/20 (i.e. the final file is 1/20 or less of the original bmp size) will start to become more and more detectable, with unsightly flaws generally called "jpg artifacts."

BMP always saves everything just perfectly. The file format called TIF (also known as TIFF) also does so.

If you, for one reason or another, wish to save uncompressed perfect renditions of your images you would be wise to use TIF and not BMP since TIF is universal standard readable on both IBM and Apple type computers, while BMP format is invented lately by Microsoft for Windows (i.e. IBM type) computers and is thus not as universal.

Generally, consumer type images can be stored as jpg, while highly important images such as hospital x-rays and battlefield satellite images are saved as bmp or tif, for obvious reasons.

-bruce

-- bruce komusin (bkomusin@bigfoot.com), February 06, 2000.