Changing DPI on Canon Rebel

Haystack

My friend and I have digital rebels. My shots come out at 180 dpi and hers come out at 72 dpi. Can't for the life of me figure out how to change that setting. Anyone know?:dunno

ziggy53

As far as I know, there is no way for the setting to be changed. If you shoot and save in RAW format, many RAW conversion software programs allow you to choose the output file dpi setting.

I think you can automate JPGs to losslessly convert to another dpi using software like IrfanView, but it does require a batch operation and I don't think you can record back to the original filename and subdirectory in a single operation (nor would you want to.)

ziggy53

TristanP

Where exactly are you getting that info from? Is it PS info, properties of the pics themselves? My 20D reports them as 72 dpi (which is a complete misnomer because dpi only refers to actual printed output). PPI is a meaningless measurement until you print the file.

cmason

DPI is meaningless on cameras and is therefore not set in the camera. The difference is likely in the software you are using, and the default settings in that software. Change the default to whatever you like...I have mine set at 300.

Haystack

Hello,

This information is coming from image size in photoshop cs2. just thought it was strange how they were different and no way to change it in the camera - but it makes sense that if it only is used for printing output there wouldn't be a need to change it in the camera-and it is a default in the program.

I am creating a book at fastbackbooks.com and they require 300 dpi images. I upsized my photos to that and it will be interesting to see if they turn out awful or not. I always worry a bit when I upsize.

Thanks for your help all.

mercphoto

Haystack wrote:

I am creating a book at fastbackbooks.com and they require 300 dpi images. I upsized my photos to that and it will be interesting to see if they turn out awful or not. I always worry a bit when I upsize.

300 dpi, sure. But at what image size? DPI is meaningless unless you know the inches as well (the "I" part).

300 dpi at 4" by 6" is 1200 by 1600 pixels. 300 dpi at 8" by 12" is 2400 by 3200 pixels. Big difference, right? I'm still surprised the publishing industry can't figure this simple thing out.

ziggy53

Folks,

The camera is assigning an arbitrary dpi to the tag in the EXIF. It really does cause problems in that even PhotoShop uses this information and gets confused when compositing images of dissimilar dpi, for instance. It is not just a printing and display problem.

Should this be the case? Of course not, but please don't bash Haystack and others for identifying the problem and having to deal with it.

So go ahead and blame the camera manufacturers for making this setting a non-changeable tag, and blame the software manufacturers for not having more usefull automation in dealing with it.

When PhotoShop senses a colorspace other than the working color space, it pauses the File Open operation to ask the user which color space to use or convert to. Would it be asking too much for the software to ask which dpi/ppi the user wishes and allow a user default?

This part of digital imagery is still in the "Dark Ages" of development I'm afraid.

ziggy53

ziggy53

Haystack wrote:

Hello,

This information is coming from image size in photoshop cs2. just thought it was strange how they were different and no way to change it in the camera - but it makes sense that if it only is used for printing output there wouldn't be a need to change it in the camera-and it is a default in the program.

I am creating a book at fastbackbooks.com and they require 300 dpi images. I upsized my photos to that and it will be interesting to see if they turn out awful or not. I always worry a bit when I upsize.

Thanks for your help all.

Haystack,

All you need to do is not select the "Resample" when you change the "Resolution" in the "Image Size" dialog box. Also use quality level 12 when you re-save the image to avoid JPG recompression artifacts.

Like this:

ziggy53

Haystack

Thanks Ziggy.

Actually I followed Scott Kelbys resizing tutorial in The Photoshop CS2 Book for Digital Photographers, he recommends you upsize to whatever dpi and select bicubic sharpener.

Now - I don't know the difference between that and not resampling. I will try your method also.

ziggy53

Haystack wrote:

Thanks Ziggy.

Actually I followed Scott Kelbys resizing tutorial in The Photoshop CS2 Book for Digital Photographers, he recommends you upsize to whatever dpi and select bicubic sharpener.

Now - I don't know the difference between that and not resampling. I will try your method also.

Haystack,

The printer RIP (Raster Image Processor) also does resampling (usually quite well), so unless you exactly match their print size "and" resolution, you can actually degrade the image over just letting the RIP handle it from original (double manipulation). You also have much larger file sizes and risk the JPG recompression artifacts I mentioned before, when you resize and resample and save (unless you use like a TIF file and RLE compression, which is lossless).

It looks like Fastback Creative Books likes to use Adobe InDesign and finished printer-ready PDFs.

If you have InDesign, you should be able to just drop the image into a frame, and then the output should go to a PDF using their PDD.

If you use another publishing program, the procedure would be similar, except in very simple word processors, where you would simply use a PostScript print driver to print to a PS file and then process with Acrobat Distiller to get the PDF.

If you are using Fastback Creative Books services to do your layout, you need to follow the guidelines in the "Preparing Your Files" document, which I'm afraid I just don't have time to read. I suspect that except for the "resolution" requirement, and maybe a minimum total file size for the intended frame, you are still better off letting them resize and upsample, if required.

ziggy53

mercphoto

ziggy53 wrote:

Should this be the case? Of course not, but please don't bash Haystack and others for identifying the problem and having to deal with it.

I'm not exactly sure who was bashing Haystack. :shrug

Haystack

Never felt bashed, no worries...

Ziggy-thanks for that explanation. I layed it out in Indesign, exported to print ready pdf and used tif's. Fastback books is the only company I have come accross that requires photgraphs to be in tifs, seems like all others want Jpegs. Will be interesting to see how it comes out.