Difference between TIF & JPG

[Brian_A]

Maybe someone can answer this one for me because it's kicking my ass.

When I have my image open in Photoshop, it looks just fine as a TIF. When I save out to JPG it looks like complete crap. I understand I'm jumping from 16 to 8 bit, but it still looks fine when I make that conversion.

Here's an image as an example...

http://www.AkersonStudios.com/temp/bench.jpg

That roof should actually be a greenish brown. Anyways, if anyone has any suggestions, I'd appreciate it. My monitors have been recently calibrated, just for reference.

[Peter De Smidt]

I don't know if this is your problem, but generally Web images should be in sRGB, whereas people often edit the photo in Photoshop in another color space, such as Adobe 1998. If the jpg is in a color space other than sRGB, then it'll look funny on the web.

Before saving as a jpg, use Edit>convert to profile in Photoshop. This will tell you what the current color space is, and it'll give you the option to convert to sRGB, which you want to do for the web. After that, make sure the image is in 8 bit mode and save as a jpg.

Hope this helps.

[Brian_A]

Just out of curiosity, why would you want to give an image a smaller color gamut? I'll have to try your idea though. Thanks for the response! -Brian

[Keith S. Walklet]

SRGB color space was developed with the web in mind. A smaller, compressed color space to expedite image loading. For printing, it is clearly not a desirable color space as compared to something larger, such as Adobe RGB. Charlie Cramer calls it "Satanic RGB." I've also seen "Sucky RGB" and "Stupid RGB."

[Archphoto]

I don't know what setting on the .jpeg's you are using, but it should be at the highest setteing: 12, in that way you loose as little as possible.

Peter

[Andy Eads]

Just to be clear, there are two problems at hand. The first is what level of compression have you chosen? The recommendation to use 12 is good if file size is not an issue. Quality level 12 introduces the fewest artifacts such as banding in smooth areas like the sky.

The second problem revolves around color management. From image capture to the final display, you have to make some choices about the qualities you want to preserve and whether you may be using these photos for some other purpose down the line. I suggest you check out a book on color management by Andrew Rodney.

[Marko]

Just out of curiosity, why would you want to give an image a smaller color gamut? I'll have to try your idea though. Thanks for the response! -Brian

Because most computer screens out there are limited to sRGB and because most browsers are not ICC-aware, your image will simply get squeezed into the available color space without proper conversion. Therefore, you want to convert your image to the same color space prior to saving for Web in order to make it look right.


I don't know what setting on the .jpeg's you are using, but it should be at the highest setteing: 12, in that way you loose as little as possible.

Peter

That will also give the largest file size. Jpg is a compressible format, made specifically to allow reaching the best compromise between file size and image quality. The level of compression at which this point is reached varies from image to image. The best way, IMO, is to use Save for Web (in Photoshop) instead of Save As... That will allow you to vary the compression and a few other parameters while watching the preview AND the resulting file size. It will also avoid saving the thumbnail and other information that is useless for the Web but still increases file size.

[Andy Eads]

I'm a little too fast to post a reply some days. Here is a better response to your original question.

A TIFF image is one that contains a data set for each pixel captured. The data are the color values for that pixel. TIFF images can be compressed in a way that does not introduce any artifacts (lossless)but the level of compression is not adjustable.

A JPEG image is one that started life as a TIFF but has been compressed using a method that is adjustable but is lossy. That is, some element of detail or color may not be restored when the image is decompressed. A TIFF file from a Nikon D70 will be about 17M bytes while the same image saved as a JPEG at best quality will occupy around 2.4M bytes.

There is much more to this story such as bit depth. Again, I suggest you do a little reading to gain understanding.

I hope this helps.

[walter23]

Just out of curiosity, why would you want to give an image a smaller color gamut? I'll have to try your idea though. Thanks for the response! -Brian

Because the smaller gamut is the standard and assumed default for a lot of web browsers which aren't smart enough to look up the colour space of an image.

[Kuzano]

If image quality had been higher up the list of importance when JPEG was originally introduced, it may have been a more justifiable program to use today. JPEG's primary purpose was for the reduction of storage space requirements. It happened at a time when most data transfer over the internet was dial-up and when storage memory was expensive and drives were small. Sometime, look up the mission of the Joint Photographic Experts Group in developing JPEG.

JPEG is very successful for what it was originally designed to do. However it is a "lossy compression" algorithm that lets the user dial in the degree of agressiveness on it's destructive capability. It, quite literally, throws away data from RAW or TIF files.

That's a simplistic answer for you, but the bottom line is that JPEG should never be a part of any work flow that requires the highest image quality.

It's uses should be limited to making files transportable, or web viewable, while it is destroying the quality of the image in some respect at the same time, and to the degree the user sets the percentage of compression.

So, the question ultimately comes down to, given the power and storage space on most comtemporary computers, why do we even use it, other than for the two reason I mentioned previously?

[neil poulsen]

Maybe someone can answer this one for me because it's kicking my ass.

When I have my image open in Photoshop, it looks just fine as a TIF. When I save out to JPG it looks like complete crap. I understand I'm jumping from 16 to 8 bit, but it still looks fine when I make that conversion. . . .



When the image degrades, are you looking at both the TIFF and the JPG in Photoshop, or are you looking at it on the web using a browser? If the web, how did you upload the image? (e.g. through IWEB, through FTP, etc.)