BMP 2 JPG without Dithering?

(Is dithering the correct word?)

When I have a bitmap picture (that I probably got from Print Screen) and I save it as a jpeg, it gets all messed up. Is there any way around that? Thanks in advance.

AR

I dont know if this exactly answers your question, but:

BMP is a pure, uncompressed format. Every pixel you see on screen is stored directly in the BMP file.

JPG is a compressed format. Groups of pixels are compressed according to the JPG algorithm and then stored in the JPG file. Some data is generally lost during this translation.

One thing thats very important here is the "level" of JPG compression you chose. This will depend on the tool you are using for the format conversion. Better tools, such as Photoshop, offer you a choice of compression levels when you save something as a JPG. Choose "high quality" rather than "high compression" in order to improve your picture quality.

(If you can mention the tool you are using or the exact problem you are seeing with the JPGs, then people may be able to provide more help. For instance if the JPG has "jaggies" that means everything is working right, but your compression setting is too high. If the JPG is just a random jumble of pixels, something more serious has gone wrong.)

IIRC the JPG format is lossy, which is what Gizzard described above - you lose some resolution, but have vastly smaller file sizes. You can try raising the compression (and thus raising file-size) - PSP, Photoshop, and GIMP can do this easily (and GIMP is free!).

The word is artifacting, fyi. Dithering is where a color is simulated by displaying a pattern of several other colors. If you save a 24-bit bmp as a gif, for instance, you'll get dithering because gif only supports 8-bit (256) color. Artifacting is where lossy data compression creates undesireable "weirdness" and is common is JPEGs.

The key to reducing artifacting is using a better program, as mentioned. The JPEG format supports a wide variety of quality settings. In a high-end program like Photoshop you can save out very low quality JPEGs (but with a tiny file size), you can save out very high quality JPEGs (but with a commensurate large file size) JPEGs, and you can save out anything in between. Definitely get a better tool and then save it with a higher quality setting.

Thanks for the info. Here's an example of what I mean:

first pic is the bmp version 66k
second pic is the jpg version, minimum compression 15k
third pic is the jpg version, medium compression 4k
fourth pic is the jpg version, maximum compression 2k

AR

Yup, that's artifacting. As mentioned, the jpeg format is a lossy compression method, meaning some information is thrown away to help keep the file size down. The more you compress it, the more info is thrown away and the worse the artifacts get.

Even the best jpeg compression will throw away some data, and will generate artifacts. The key is to find the balance for a particular picture where the artifacts are least noticeable and the filesize is acceptable. The pictures you attached are particularly bad because of what jpeg is designed for. The algorithm is meant to be applied to 'natural' pictures: landscapes, skintones, etc. Content with harsh or sharp lines such as text always get mangled by jpeg. For these types of pictures, I usually prefer using the png format, it's losless (no information loss), though it generates bigger file sizes.

Here are two other versions (from your bmp). The first is Photoshop's Save for Web "JPEG High" version, the second if Photoshop's Save for Web "128 bit GIF". Both look pretty clean to me and are reasonably sized.