I've moved this to a new topic by itself. Are you talking about changing the quality as they appear in Photoshop, or in your output from InDesign?
Anytime you reduce the image size you risk some loss of image detail, but how much depends on the amount of reduction and the individual image. That said, most output settings from InDesign are going to downsample your images if they are over some resolution value of your choice, and if you are printing, the RIP or your printer may throw out excess image data even if you don't downsample, so this is a difficult question to answer with a single definitive response.
- If possible, determine the physical size of the images in the layout, and size the images in Photoshop accordingly before you place them.
- If that's not an option, work with small placeholder jpgs to begin with, and replace them with high quality images when their size has been established.
Remember that if you resize images in Indesign, the ppi will change. In the screenshot below, the placed image that originally was 150 ppi has become 307 ppi because it has been scaled down..
- Make sure that the images are 8-bit, not 16-bit.
- Set the image size as shown in the screenshot below. Make sure that the padlock icon is active (constrains proportions) and check Resample.
300 ppi is commonly used for offset printing, but check with your printer. If you reduce the ppi, file size will also be reduced.
are very large (some pictures might be 20mb)
20mb doesn't seem very large relative to the current cost of storage—which runs around 4 cents a GB—so your 600 images at 12GB would cost 48 cents to store. Are you really willing to resample and permanently loose the higher quality originals? If you link the files the ID pagelayout file size will be manageable and you can then compress and resample a PDF version of the ID layout without compromising the original photographs.
xatzis123, I always presume that people will work on copies of their original images if resizing them using lossy resampling/interpolation.
As Rob points out, storage is cheap. Are you losing performance due to having all of these images in the file?
As Per notes you may have very high effective PPI values.
If you do use the scripts linked in my previous post, ensure that you work on copies of the original layout and linked images, such as using the package option to generate a copy.
On your previous message you said that: "Remember that if you resize images in Indesign, the ppi will change. In the screenshot below, the placed image that originally was 150 ppi has become 307 ppi because it has been scaled down.."
I can't understand how reducing the images is increasing the ppi. Shouldn't be reducing the ppi as reducing the file size?
Also, i have seen that you are using jpeg images. I was using jpegs but i couldn't place something behind the image size frame without cutting everything sourounding the frame. look at the picture bellow:
Another question is: when placing images to InDesign, images has to be in CMYK or RGB? Because later on i am exporting the file to Press Quality pdf and converting the files to CMYK.
I have a screenshot of a linked image details in InDesign. As you can see the actual ppi is 300 but the effective ppi is 667. Are those values too big for today's printing machines?
Also the scale is 45%. If i reduce the dimensions so the scale is 100% will that affect the image quality when printed?
can't understand how reducing the images is increasing the ppi. Shouldn't be reducing the ppi as reducing the file size?
When you scale an image you are scaling the size of its pixels. So if the actual image res is 100ppi and you scale the image to 50% a pixel becomes half it's original size--there are now 200 pixels per inch.
Also the scale is 45%. If i reduce the dimensions so the scale is 100%
If you change the image dimensions so that it can be placed at 100% the actual and effective resolutions will match—the effective res is the output resolution. Lowering the resolution in PS to some target res like 300ppi is usually not worth the effort — it certainly won't improve quality.