Posted by Tim Behle on September 2, 2007 at 1:45 PM
I'm finding out in another thread, that everything that I thought I had learned about posting pictures on the Web the last 15 or so years was wrong. I have always had the belief that by reducing a file from 300 pixels, down to 72 (or 96) would make it hard for anyone to copy that file, increase it back to 300 dpi and have a usable image. That it would depend more on file compression. What is Jpeg compression and how does it work? Could it help me to protect my pictures?
Posted by Paul DeCesare on September 3, 2007 at 1:07 AM
Hi Tim,
JPEG is a small file size at a cost. EVERY time you save, it compresses the image and degrades quality. Your size doesn't change, but the quality degrades. You always, always, always only want to save a JPEG ONCE. Always work on your images in another format such as TIFF or PSD if you have Photoshop, and then when you're ready to send it up to the Web, save it as JPEG. Now to answer your question: if you want good quality on the web when viewing, first and foremost, make sure you are in the sRGB colorspace (good for Web, not so much for printing... Adobe1998 is good for printing). Then save the image as 96 or 72 dpi (I use 96), and make the short side of your photo divisible by 12 (i.e. 240, 480, 960 pixels), depending on how big of an image you want to display. This yields good results, and you want the sRGB colorspace because that's what web browsers can render. NOW, image protection: The bigger you display, the easier it is for someone to upsample the image and print it (although there are limitations). If you have a standard 3:2 image file (let's say a 3000x2008 like I get from my Minolta 7D), and you want to display it w/o fear of someone rehydrating it for print, make the short side no bigger than 240 pixels at 96 dpi (i.e. 360x240). The image won't be huge, and that's the protection. Actually, since someone can do a screen capture, DPI is almost irrelevant here. The caveat is the image size. Give 'em a 180x120, and they won't be able to do much print-wise!
Hope this helps.
Posted by William Callis on September 3, 2007 at 1:37 AM
Reducing your images to 72 dpi for the web would make the file pretty much usless for someone that would want to make a print from your image. There's not much you can do to protect your images from being used elsewhere on the web short of stamping an ugly copywrite notice across your picture. Jpeg compression is a method of reducing the size in megabytes/kilobytes of an image without reducing the image size with respect to pixel size. I does this at the cost of image quality. There are some ways to make image theft more difficult. There are softwares available that are specifically designed for that purpose. You can also try a Flash website. Even with these precautions all a user has to do is press his "print screen" button and they'll have a low grade copy of any mage saved to their computers memory.
Personally I don't worry too much about those issues.I own the copywrite of my images and I can do what I wish with them. No one can take that away from me. A person that would steal from me wouldn't purchase my work even if it were not available for theft. If I ever get so fortunate someday that I had a well known reputation as a photographer I won't have to put my photos on the internet anymore.
Good Luck,
Bill
http://portfolio.bcallis.com
Posted by Richard Ditch on September 3, 2007 at 12:57 PM
Before you get flooded with lots of incorrect information again about dpi (totally irrelevant to jpeg compression and protecting content from theft), here's what jpeg compression is about.
It simply looks for groups of adjacent pixels that are ALMOST the same and uses a SINGLE set of RGB values to represent that group of pixels. So, jpeg compression works great when the image has lots of areas with very little variation, such as a uniform color sky. It doesn't work very well when there is lots of variation across the frame - highly textrued surfaces such as fine feather detail or an autumn leaves landscape with lots of color variation. To get these variations to compress you must increase the amount of variation you are willing to replace by a SINLGE RGB value - essentially you toss out color change and texture for smaller file size.
Now, before you get flooded with incoorect info:
the only thing that matters for web wiewing is TOTAL PIXELS, and not DPI/PPI. 400 pixels x 600 pixels is exactly the same at 10 ppi as it is at 1000 ppi. When a viewer downloads you image they will get the same 400 x 600 pixels and can try to print it at whatever dpi their software charges it to. By setting the ppi to a large value you can force the thief to making a very tiny print only if the thief is too stupid to know how to reset the dpi value in the printing application.
You are almost completely CORRECT. As long as downloading a file gets all of the data, it does not matter whether it was set for 72, 96, 10 or 1000 dpi. But, you must download all of the file. When with some ISPs which further compress web display data, when doing a "Save as" one will get all of the data. Otherwise, one could not safely download software, etc.
Reading a comment on the thread about 72 vs 96 dpi, it appears that some of the dial-up services which advertise higher "through put" are in fact reducing the amount of data being delivered. The "through put" is actually the same, but the amount of data is reduced giving the illusion of increased speed. The result may be faster loading images, but they are of significantly reduced quality. However, with a broadband connection there is no degradation and therefore absolutely no effect of specifying the resolution. Thus, setting the resolution at 72 dpi would NOT protect an images as erroneously advised above.
Discussion
4 repliesJPEG is a small file size at a cost. EVERY time you save, it compresses the image and degrades quality. Your size doesn't change, but the quality degrades. You always, always, always only want to save a JPEG ONCE. Always work on your images in another format such as TIFF or PSD if you have Photoshop, and then when you're ready to send it up to the Web, save it as JPEG. Now to answer your question: if you want good quality on the web when viewing, first and foremost, make sure you are in the sRGB colorspace (good for Web, not so much for printing... Adobe1998 is good for printing). Then save the image as 96 or 72 dpi (I use 96), and make the short side of your photo divisible by 12 (i.e. 240, 480, 960 pixels), depending on how big of an image you want to display. This yields good results, and you want the sRGB colorspace because that's what web browsers can render. NOW, image protection: The bigger you display, the easier it is for someone to upsample the image and print it (although there are limitations). If you have a standard 3:2 image file (let's say a 3000x2008 like I get from my Minolta 7D), and you want to display it w/o fear of someone rehydrating it for print, make the short side no bigger than 240 pixels at 96 dpi (i.e. 360x240). The image won't be huge, and that's the protection. Actually, since someone can do a screen capture, DPI is almost irrelevant here. The caveat is the image size. Give 'em a 180x120, and they won't be able to do much print-wise!
Hope this helps.
Personally I don't worry too much about those issues.I own the copywrite of my images and I can do what I wish with them. No one can take that away from me. A person that would steal from me wouldn't purchase my work even if it were not available for theft. If I ever get so fortunate someday that I had a well known reputation as a photographer I won't have to put my photos on the internet anymore.
Good Luck,
Bill
http://portfolio.bcallis.com
It simply looks for groups of adjacent pixels that are ALMOST the same and uses a SINGLE set of RGB values to represent that group of pixels. So, jpeg compression works great when the image has lots of areas with very little variation, such as a uniform color sky. It doesn't work very well when there is lots of variation across the frame - highly textrued surfaces such as fine feather detail or an autumn leaves landscape with lots of color variation. To get these variations to compress you must increase the amount of variation you are willing to replace by a SINLGE RGB value - essentially you toss out color change and texture for smaller file size.
Now, before you get flooded with incoorect info:
the only thing that matters for web wiewing is TOTAL PIXELS, and not DPI/PPI. 400 pixels x 600 pixels is exactly the same at 10 ppi as it is at 1000 ppi. When a viewer downloads you image they will get the same 400 x 600 pixels and can try to print it at whatever dpi their software charges it to. By setting the ppi to a large value you can force the thief to making a very tiny print only if the thief is too stupid to know how to reset the dpi value in the printing application.
You are almost completely CORRECT. As long as downloading a file gets all of the data, it does not matter whether it was set for 72, 96, 10 or 1000 dpi. But, you must download all of the file. When with some ISPs which further compress web display data, when doing a "Save as" one will get all of the data. Otherwise, one could not safely download software, etc.
Reading a comment on the thread about 72 vs 96 dpi, it appears that some of the dial-up services which advertise higher "through put" are in fact reducing the amount of data being delivered. The "through put" is actually the same, but the amount of data is reduced giving the illusion of increased speed. The result may be faster loading images, but they are of significantly reduced quality. However, with a broadband connection there is no degradation and therefore absolutely no effect of specifying the resolution. Thus, setting the resolution at 72 dpi would NOT protect an images as erroneously advised above.