Photoshop DPI question

[Psydrop]

I have a very large file (psb) for print, can i change the dpi to lets say 50 and work on it that way, and when it is finished change it back to 150dpi without losing quality?

It is way easier to work that way, sincs working at 150 is immensely slow.

Thanks!

 

[WV1989]

No, I would'nt advise this. You will lose quality.

 

[Psydrop]

So my only option is to work really slow? (or ask my boss for a MacPro)

 

[MrToM]

Despite what you may see in any PS dialogs, images don't have a DPI as it's a printer setting....dots per inch....the 'dots' being dots of ink.
(And before anyone say's anything when I say 'printer' I refer to that lump of cheap plastic sat on a desk with the extortionately expensive ink in it....not the guy down the road that will 'fit you in' after his lunch.)

If you mean PPI as in Pixels Per Inch then yes, by all means you can change it but it won't affect the size of the image as its a value used by the printer to determine how 'big' to print your image.

You can however re-sample the image using PPI as one of the re-sample values in the settings, but in doing so you will PERMANENTLY lose those pixels thrown away by the process.

Re-sampling back UP from a down-sampled image will not retain the same 'quality' as the original.

In short, PPI has no affect on digital images but can be used for re-sampling.
Re-sampling should be avoided at all costs as loss of 'quality' is not preventable.

So in a word, no, I wouldn't touch it.

Regards.
MrTom.

 

[WV1989]

It's not about working "really Slow" its about how do you want the end product to look.

Mr Tom, has answered properly.

 

[Psydrop]

Offcourse I want it to look good, the workflow is just really slow, since when I make an adjustment (let say transform a layer) I have to wait 4 minutes..

Anyway, thanks for the answers.

 

[MrToM]

Is it possible for you to work on just a small area rather than the image as a whole?

If so, you could divide the image into, say, four parts.....save each part as its own PSD file and then use 'Place Embedded' to preview all the parts together when you need to.

This does of course depend on your version of PS.

Regards.
MrTom.

 

[Tom Mann]

What you are suggesting is common practice in the billboard / very-large-format-printing industry.

First, go to: http://graphicdesign.stackexchange....on-should-a-large-format-artwork-for-print-be

Scroll about 40% down the page to the section titled, "Raster Image Data" and read it.

Basically, in contrast to some of the other posts in that thread, this section (#11) is written by a knowledgeable person, and says that for printing large items, you rarely need the high ppi numbers that you might think you need, and often, surprisingly low ppi numbers are entirely adequate, and even preferred by the printing company.

Then, and only IF you have established that you actually need the 150 ppi that you stated in your first post, and can't work at 50 ppi (ie, with smaller pixel dimensions), there is a technique called, "scaling" that is also very commonly used in the billboard industry. It is done exactly for the reason you gave.

The basic idea behind this technique is to do all of the development and refining of the adjustments that your image may need on a low resolution (ie, low pixel count) surrogate version of the image, and then, if the adjustments are mostly adjustment layers, you can just pull the layers over from the surrogate to the unwieldy, full resolution version with the high pixel dimensions. You bring all the adjustment layers over, and let PS chew through them only once. This way, you are not waiting 4 minutes every time you want to do an experiment with a slightly different adjustment.

The basic idea that I described in the previous paragraph runs into problems if your work on the image includes sharp edged, detailed layer masks, compositing, or local (not global) adjustments. If you need to do such things to achieve final product, you may have to do things like develop your layer masks or component images on full rez versions of those images, and bring them into your final PS file only once, near the very end of the process. The speed advantage of generating detailed masks and component images separately comes from the fact that you can do such work in one or more separate files, each with the absolute minimum number of layers, maybe as few as one layer, so you are taxing your computer resources vastly less than trying to do something like develop a detailed mask in a file that might have dozens of full rez layers.

HTH,

Tom M

 

[ALB68]

One could make a good case here for use of vector images. It just doesn't seem practical to create output for a huge sign as a bitmap image but I suppose one has to do what fits the situation.

 

[Hoogle]

Have you setup photoshop properly to suit your needs. ie in performance settings have you increased the ram which your allowing photoshop to use if you have 16gb of ram then increase it to 12gb which photoshop can run at if you have 8gb then try setting it to 6gb never set it to use 100% of your available ram as it will cause your computer to freeze.

if your still having problems then maybe go down the approach of resizing the image while working on it and using a specific method of resizing it back up when ready to print. I am not saying this is the best idea but you may get away with some good scaling once again it depends on the type of image on what method you use or if you use a 3rd party plugin for it. I must stress it is a lot easier to downsize an image and retain quality but a lot harder to blow up the image and keep the desired quality.

 

[Tom Mann]

You are absolutely right about trying to vectorize it if at all possible, but many billboards contain photos and other images that can't be vectorized without imparting a completely different look. So, the best one can do is to work on each of the bitmapped areas in separate PS files, using low rez surrogates along the way, if possible and necessary, and then put them together with the vector parts in AI or PS as a near-final step.

T