Hi Monika,

I haven't experienced a loss in quality with scaling photos smaller; as you mentioned, loss of quality will occur with enlargements.

Are you scaling before you crop the photos? How are you scaling (I scale with Image->Scale Image). What are your original & target sizes?

Regards,

Erik.

Monika Himpelmann wrote:

Dear all,
I have a question and maybe it is easy to answer and has been answered before although I didn't find it in the FAQ's.

When I try to scale a foto in order to get it passport photo size it looses quality. The fotos I want to scale are of good quality but too large and are showing not only the head and upper chest of people but often more and so I have to cut them which is possible without any problem and then scale them in the format I need.

I would understand the loss in quality if I would try to enlarge the fotos but making them smaller in size should not make them loose quality???

Any hints from you out there? Thank you in advance for any answer.

Best wishes Monika

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On 08/17/2009 11:33 AM, Monika Himpelmann wrote:

Dear all,
I have a question and maybe it is easy to answer and has been answered before although I didn't find it in the FAQ's.

When I try to scale a foto in order to get it passport photo size it looses quality. The fotos I want to scale are of good quality but too large and are showing not only the head and upper chest of people but often more and so I have to cut them which is possible without any problem and then scale them in the format I need.

I would understand the loss in quality if I would try to enlarge the fotos but making them smaller in size should not make them loose quality???

Any hints from you out there? Thank you in advance for any answer.

Best wishes Monika

Monika,

I agree that it does not make sense to loose quality when scaling smaller.

The only thing I can think of is that if the photos are JPEG / JPG (or some other "lossy" format then, *EVERY* time a photo is saved it looses quality. If somehow in the process you are saving it multiple times, then you might loose quite a bit of quality.

With JPEG (that you want to keep as JPEG) that best method is probably to make a copy of the file and then open the copy in Gimp. Do all your work on it (scaling, cropping, etc.) WITHOUT doing any saving until you are DONE. Then save it. When you do that "save", select the highest possible quality setting.

If in the future you have to open the file for some reason (for example, printing) do NOT save it again in the process of closing it (unless you have specifically made some change that you really intend to save -- but understand you will lose some quality.

If that is not the problem, then the situation really does sound odd.

Jay

Jay Smith wrote:

Monika,

I agree that it does not make sense to loose quality when scaling smaller.

I'm confused I think. Isn't scaling smaller an inherently lossy process? If there's information in a section that's 20 bits across and it gets reduced to 5 bits across it isn't possible to still contain the same information, is it?

Patrick

On 08/17/2009 06:38 PM, Patrick Horgan wrote:

Jay Smith wrote:

Monika,

I agree that it does not make sense to loose quality when scaling smaller.

I'm confused I think. Isn't scaling smaller an inherently lossy process? If there's information in a section that's 20 bits across and it gets reduced to 5 bits across it isn't possible to still contain the same information, is it?

Patrick

As you state it, my understanding is, yes. Scaling smaller is a "lossy process". But at higher compression (more lossy) settings, JPEGs can be extremely lossy. Hopefully, however, when scaling smaller, there is adequate data in the image to not result in actual visible loss of quality in the image (other than it is smaller, etc.).

However, my point was that if the user is one who, perhaps simply out of habit, saves every time they do anything, a JPEG can be turned from sharp and clear into visual mush after just a few saves.

Back in the days when I was using Photoshop on Windows 95 on a 128 MB memory machine, I _did_ save every time I did anything simply because Windoze was going to crash -- it was not a question of IF it was going to crash, it was only a matter of WHEN. (But... I was editing TIFFs, not JPEGs, so there was no "lossyness".)

Jay

On Mon, Aug 17, 2009 at 10:33 AM, Monika Himpelmann wrote:

I would understand the loss in quality if I would try to enlarge the fotos but making them smaller in size should not make them loose quality???

Any hints from you out there? Thank you in advance for any answer.

Are the images in RGB mode? (Image->Mode->RGB) Scaling indexed images can cause problems...

Chris

On Monday 17 August 2009, Monika Himpelmann wrote:

Dear all,
I have a question and maybe it is easy to answer and has been answered before although I didn't find it in the FAQ's.

When I try to scale a foto in order to get it passport photo size it looses quality. The fotos I want to scale are of good quality but too large and are showing not only the head and upper chest of people but often more and so I have to cut them which is possible without any problem and then scale them in the format I need.

I would understand the loss in quality if I would try to enlarge the fotos but making them smaller in size should not make them loose quality???

Sorry if I cover ground that has already been trod. I haven't had time to follow the discussion before now My take:

scaling an image to a smaller size forces the program to interpret a group of pixels as a single color/pixel which leads to blockiness and lost quality.

If I were trying to reduce the size of an image while preserving definition I would look at changing its resolution ie from 72pix x 72pix to 288pix x 288pix, reducing the images apparant size (to 1/4 the starting size) while keeping all the pixel information. This could be done at the time of printing (setting the printer resolution) or within gimp.

If I am in error please let me know

HTH

On 08/17/2009 08:33 AM, Monika Himpelmann wrote:

Dear all,
I have a question and maybe it is easy to answer and has been answered before although I didn't find it in the FAQ's.

When I try to scale a foto in order to get it passport photo size it looses quality.

Seems like a confusion about the scaling process. Your printer probably prints color at 300 or 600 dpi. When you work on that size of an image on your computer screen, your computer monitor probably only displays about 96 dots per inch (pixels per inch). That means that at 100% size, the photo will look HUGE on your computer screen at 100% zoom. That is how it is supposed to be. At 100% size on a printout from your printer, the photo will be much smaller, because your printer uses smaller dots to print the image.

It's like a mosaic made of tiles. If I give you tiles that are the size of your fingernail, and tell you to create a smiley-face mosaic with those tiles, you'll have a fairly small mosaic. But if I give you the same number of tiles that are the size of dinner plates, your mosaic will be much bigger. But both mosaics have the same amount of detail, because you're working with the same number of tiles.

Printer = small tiles (dots) Monitor = big tiles (pixels)

If you use the scale image command to resize your image in GIMP before printing, you are losing quality and will print an inferior quality image.

This may help you: Some people prefer to save the "huge" image from GIMP in PNG format, then import that photo into e.g. OpenOffice and scale the photo to size (in inches or cm) there. When you print, you'll have a nice high-res photo.

If I were trying to reduce the size of an image while preserving definition I would look at changing its resolution ie from 72pix x 72pix to 288pix x 288pix, reducing the images apparant size (to 1/4 the starting size) while keeping all the pixel information.

HTH

I agree with this completely. I make a lot of sigs for people that normally cannot exceed 500x200px. As such I will use many photos/pic that need to be rescaled to a much smaller object. The only way I have found to maintain clarity is to change the resolution to a much higher res. Nothing else has worked for me.
Mark (via www.gimpusers.com)

Von: "Mark"

I agree with this completely. I make a lot of sigs for people that normally cannot exceed 500x200px. As such I will use many photos/pic that need to be rescaled to a much smaller object. The only way I have found to maintain clarity is to change the resolution to a much higher res. Nothing else has worked for me.

Interesting. If you change the resolution from e.g. 72ppi to 300ppi, the image data stays the same, so it's hard to believe that this should have any effect on scaling or other transforms.

Can you prove that it does have an effect?

Michael

Il giorno ven, 21/08/2009 alle 13.45 +0200, Mark ha scritto:

If I were trying to reduce the size of an image while preserving definition I would look at changing its resolution ie from 72pix x 72pix to 288pix x 288pix, reducing the images apparant size (to 1/4 the starting size) while keeping all the pixel information.

HTH

I agree with this completely. I make a lot of sigs for people that normally cannot exceed 500x200px. As such I will use many photos/pic that need to be rescaled to a much smaller object. The only way I have found to maintain clarity is to change the resolution to a much higher res. Nothing else has worked for me.

I usually apply two or more times the sharpen filter before scaling the image at a lower size. To obtain better results I perform one or more intermediate steps before getting the desired size (for example, to reduce a 3000x2000 image to 900x600 I apply few times the shapening, then resize to 1200x800, then sharpen again few times, then reduce to 900x600).

Marco