One of our clients at work demands the lowest filesize possible for their jpegs causing us to use the save-for-web function. However they also require that the jpegs be 72 dpi. Photoshop CS2 automatically sets the dpi at 100 dpi while saving for web whether you want it to or not. Is there any way round this other then saving them through another program afterwards thus degrading the jpeg quality further?
Just scale it to 72 dpi and size it to whatever seems reasonable. You should be able to batch it with an action and save it into a seperate folder. Cliff Moore
DPI, or more correctly, PPI, is immaterial for the web. Things are represent pixel per pixel according to the resolution of the viewing screen.
I think (unless things are changed in CS2) that ppi is not even stored in a jpg saved with Save for Web.
You want to make images smaller in one of two ways: a higher jpg compression (as high as possible without ruining the image) and reducing the size of the image as much as possible. A 72×72 pixel image is only half the size of a 100×100 one, and is only slightly smaller.
Photoshop CS2 automatically sets the dpi at 100 dpi while saving for web whether you want it to or not.
Is this really true or is your Photoshop CS2 assigning a ppi of 100 to an undefined resolution in the JPG file when opening the file again? I am not at CS2 right now. Previous versions of Photoshop do not include any resolution data in the JPG file when Save for Web is used.
A 72 ppi image that is 2000 pixels wide by 2000 pixels tall is going to be bigger than a 300 ppi image that is 1500 pixels wide by 1500 pixels tall. Do your math and ask what pixel dimensions are required for this task. No web designer cares about ppi.
Thanks for all the replies. I completely understand that the dpi has no bearing when used for the web. The images are for airlines who use them on the inflight AVOD systems. To be honest i don’t think it really matters at all for them, but thats what they want and as long as windows says that the images are 72 dpi then they are happy. The problem i have is for example i will crop an image 800px x 274px at 72 dpi which will save perfectly well using save-as, but when using save-for-web it saves the image with a dpi of 100. I would just use the save-as function but some of the airlines demand tiny filesizes.
when using save-for-web it saves the image with a dpi of 100
How do you know this? Again, we ask if Photoshop is reading it as 100 ppi or if Photoshop is automatically assigning a file without resolution data a new resolution of 100 ppi upon opening? History indicates the latter.
Try opening the file in another image program to see the ppi.
I have been checking the dpi of images using program such as xn-view and Ifran-view. The images normally start off with a dpi of 300 as obtained from distributors websites and promotional cd-roms. These would then be cropped in photshop with the dpi setting on the crop tool set at 72 dpi. Then upon saving via save-for-web the dpi appears to be 100 (as checked again using xn-view and Ifran-view)
" Send them a batch of images saved at 1 dpi[Ho, you know better than to use dots ;)]"
This kind of reminds me about the time someone asked me to create a 10-up business card template for them in Photoshop at 8.5" X 11".
I did everything with paths, and the file was really tiny. The recipient was all prepared to slog through an AIM file transfer (over a glacial dial-up connection) when "TOOT!" the file I prepared showed up as an attachment in their email in box.
They were stunned, because they expected a file size of 25-30 MB; Then, I had to explain how to use it [si-i-i-i-g-g-g-g-h-h-h-].
James why don’t you resize – with or without resampling – and set the ppi to 72 (just to please the client!). Then "Save As" a Jpeg at the required compression rate. And then strip out the extraneous, non image, data.
Jpeg Cleaner will do the job effortlessly and losslessly. You can download it from Rainbow Software:
Resolution for screen use is device dependant (and almost none, btw, use exactly 72 ppi for display purposes); resolution info for screen use is irrelevant. Only the dimension matters. Educate your client.
I do not use Ifranview much but I was under the impression that XNView’s default reading resolution for any image without resolution metadata was 100 ppi. That same ‘Save for Web’ image that reads at 100 ppi in XNView reads as 72 ppi in Photoshop upon load.
The JPEG File Interface Format standard allows the pixel density to be specified as pixels/inch, pixels/cm, or aspect ratio (no specific "resolution"). If aspect ratio is specified, the application opening the file has to make its own assumptions about how the image gets displayed. Thus, it’s possible that some applications use the display resolution as specified in the OS, others use the display resolution as specified in the application, and others use the default of 72 or a fixed figure such as 100.
Mathias: You are correct insofar the application is displaying at 100% zoom. If the application is not an image editing program at 100% zoom, or a browser, it may be sized at more or less than one pixel per pixel. For example, a simplistic photo viewer may attempt to display all images within a fixed screen size, regardless of pixel dimensions. Or an application such as a word processor or a presentation program may display the image in accordance with its intended print dimensions (number of pixels/resolution) if that data is present, or at some default size.
In the case of the simplistic photo viewer – resolution info hardly matters.
In the latter cases, yes, you are correct about a print application might use the info to scale the graphics. Key word here is print (print preview, print application, etc). Just for good measure, not even the mighty Photoshop scales an image correctly, when I set the zoom level to ‘print size’ (running 1600×1200 on 15").
not even the mighty Photoshop scales an image correctly
Hmmm. You’re right.
I remember someone here saying that because most monitors display at 96 DPI (as determined from the SETTINGS>ADVANCED tab of "Display Properties") you should really work at that resolution when designing for the web to ensure it displays at actual size on the screen.
HOWEVER, a 5×5" 96 PPI image displayed at "Actual Pixels" on my 19" CRT ends up just under 6.5 inches, and at "Print Size" is displays at 4.75 inches. Windows Picture and Fax Viewer displays the same image at 6.5 inches.
Resampling the image to 72 PPI causes it to dispaly at 4.75 inches at "Print Size" and at "Actual Pixels"
Everybody, thanks very much for taking the time to reply, you’ve all been very helpful and informative. I’ve found a program, Fast Stone Image Viewer, which appears to change the dpi information without having to re-save the the image, although it can’t do this in batches. I’m also gonna check out Jpeg cleaner as mentioned above. Thanks again.
"I remember someone here saying that because most monitors display at 96 DPI …"
I think someone was mistaken. That figure (which should really be Ppi) describes what a printer will do if the image is printed from MS Paint, or some image viewer, or almost anything other than Photoshop or equivalent. Transfer the same image to a Mac and it will print at 72 ppi (using Apple’s "Preview" applet, or similar). In Photoshop, ppi/dpi is simply an instruction to the printer about what to do with the image if it is printed. There’s just no such thing as one 800 x 600 image with an image resolution of 96 dpi, and another 800 x 600 image at 72 dpi (or any other dpi/ppi). The image resolution is 800 x 600, period. Simple proof: Look at any image on monitors of different sizes. Same image–different ppi.
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