"JPG - Compression - DPI - H&M vs Photoshop - Probl

C.Trautmann · Unread post by **C.Trautmann** » Tue Dec 05, 2006 4:19 pm

I already know that my version of H&M contains bugs that other users and especially Tim dont have. So I'm cautious with reporting bugs...

But today I found something totally crazy:

Normally I take my Screenshots with Alt+Druck (ger), so that I make some Screenshot of the active window. My screen has 72 DotPerInches, dpi, like the most screens. (96 dpi for notebooks, ...)

So my screenshot should also have 72dpi, because there are no more picture-informations.

So if my picture have a length of 300 pixels and 72dpi I can compute my length in inch (300/72=4,17inch=10,583cm).

Now I took this screenshot and "paste" it into my H&M directly. Than H&M askes me where I want to save that, which compression, dpi, ... I take 100%, 72dpi and save my picture. The size is 280kb.

Now I open the fileproperties via right cklick/Properties/Fileinfo ans WOW, there is 300dpi!!!
This is bullshit, because the total lengt is 300, so the picture can only have 1inch, as soon as i printed it I measured a length of 10,583cm, or 4,17 inch.

I thought well, lets look for the dpi-number in photoshop and what a pleasure, there it is 72dpi what is logical.

At last I saved the picture in Photoshop as jpg with no compression. Now the size is not 280kb, but 120kb and the dpi-number in the properties are also different, namely 72dpi!!!

The time of saving images via copy and paste directly into H&M is now over, because our CVS-Server need place and images with the SAME INFORMATION and DOUBLE SIZE aren't enforceable.

So (at hundredth time) is it a bug or do I sth wrong. I work since 5 years in the designer-section and know much about dpi and so on. Maybe it is a way of compression in the jpg-file. But in both file-informations you will find the entry (uncompressed). All is the same, only the dpi is different (300 in the H&M and 72 in the photoshop file).

Its crazy...and im exhausted

Regards, Christoph

Unread post by **Tim Green** » Tue Dec 05, 2006 5:31 pm

Christoph,

I can confirm the DPI error when you save to JPG. When I save with 72dpi Paint Shop Pro tells me that it has 300, so the wrong DPI number is being saved with JPGs. This is a cosmetic bug.

However, remember that the DPI setting has no effect on the physical size of the image, not in any graphics program. Some annoying programs that try to think for you (like PhotoShop) may make you think that these two things are linked because they always try to resize the image when you change the DPI setting -- but that is just Adobe programmers trying to be clever. The DPI setting is really just a number associated with the image, nothing more. Some devices use it to render the image, others don't, but it doesn't do anything to the physical image file. The pixels stay the same.

PS: The automatic mail telling you that this topic had been moved got bounced back to me saying that your email address is invalid ("Recipient address rejected: User unknown in virtual alias table"). Maybe you should check it...

C.Trautmann · Unread post by **C.Trautmann** » Wed Dec 06, 2006 1:57 pm

Your answer sounds logical but I cant imagine that the dpi number is only a cosmetic thing....for print I need minimaly 300 dpi for good solutions.

So if I have some picture with 10x10cm and 100dpi, I will have 400x400 pixels. But if I have a picutre with 10x10cm and 400dpi, I will have 1600x1600 pixels, and feel certain that the filesize will increase in this case.

But my problem isnt the thing with the dpi, because this numer is wrong, the total pixel-number is the same, and the length in cm also, so the dpi-number cant be higher. But the problem is, that the filesize of my picture, directly pasted in H&M and than saved is about 200% of the uncompressed, directly pasted into photoshop and there normally saved picture.

I hope that Photoshop is stil better in picture-editing and saving than H&M

but such a difference isn't normal or?
The dpi-problem could only be a evidence for some bug...

Regards, Christoph

PS: Thanks for this information Tim, I heard such a problem 2 days ago from a friend and thought it was a random bug, but now I have to look for it...