Oversized images from Photoshop

JM
Posted By
James McNangle
Apr 24, 2006
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735
Replies
11
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Closed
I have been grumbling for a long time that Photoshop seemed to produce oversized images, but today I took a photo from the Web, clipped it in Photoshop, so it was slightly smaller, and resaved it using quality setting 7. I was astounded to discover that the saved image was almost three times as large as the original. I tried saving at progressively lower quality settings, and while the image became obviously degraded, the file size fell only very slightly. Even at quality setting 0 the new image was still almost 2.5 times the size of the original. What am I doing wrong?

I have made a demonstration page showing this effect at the web site below. The original photo was "borrowed" from the Canon web site.

http://www.corybas.com/Technical/Image_size.htm

James McNangle

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P
PiT
Apr 24, 2006
hi james,

was slightly smaller, and resaved it using quality setting 7.

i’ve checked the three pics with irfanview (image information). the original image contents no exif data – both of yours content exif information created by photoshop cs.
perhaps there you can find the real cause


PiT
HL
Harry Limey
Apr 24, 2006
"James McNangle" wrote in message

What am I doing wrong?

James McNangle

Use the ‘Save for Web’ function – I just tried a camera image from Canons site – the original was 7.71kb – I cropped it to approximately half its size and saved at 50% quality – the file size was less than 2kb. If you use the normal ‘save’ or ‘save as’ functions, Photoshop adds quite a bit of exif detail!! which does not make much difference to large images but certainly shows up in small file sizes.
T
Tacit
Apr 24, 2006
In article ,
James McNangle wrote:

I have been grumbling for a long time that Photoshop seemed to produce oversized
images, but today I took a photo from the Web, clipped it in Photoshop, so it was slightly smaller, and resaved it using quality setting 7. I was astounded
to discover that the saved image was almost three times as large as the original.

That is because you have instructed Photoshop to save lots and lots of extra data, such as color profile information, thumbnails, previews, EXIF data, and so on, in your image.

If you wish to save an image for Web use, do not use the Save As command. Use the Save for Web command. Save for Web does not save this extra data.

Or, instruct Photoshop not to save extra data in its images.


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JM
James McNangle
Apr 24, 2006
"Harry Limey" wrote:
Use the ‘Save for Web’ function – I just tried a camera image from Canons site – the original was 7.71kb – I cropped it to approximately half its size and saved at 50% quality – the file size was less than 2kb. If you use the normal ‘save’ or ‘save as’ functions, Photoshop adds quite a bit of exif detail!! which does not make much difference to large images but certainly shows up in small file sizes.

Thank you all. This seems to be the answer. I opened the original again, and selected "save for Web". It seemed only to want to save as .gif, which gave a file which was only 75% greater. But then I tried again and discovered that I could select to save as .jpg. This time I got a file which was only 4.1k, as against the original 6.67k, and was not visibly different from the original. So now I can save a lot of Web space (and loading time for viewers)!

Nothing I have read ever suggested to me that using "save for Web" would make such as spectacular difference.

Thank you again.

James McNangle
JM
John McWilliams
Apr 24, 2006
tacit wrote:
In article ,
James McNangle wrote:

I have been grumbling for a long time that Photoshop seemed to produce oversized
images, but today I took a photo from the Web, clipped it in Photoshop, so it was slightly smaller, and resaved it using quality setting 7. I was astounded
to discover that the saved image was almost three times as large as the original.

That is because you have instructed Photoshop to save lots and lots of extra data, such as color profile information, thumbnails, previews, EXIF data, and so on, in your image.

If you wish to save an image for Web use, do not use the Save As command. Use the Save for Web command. Save for Web does not save this extra data.

Or, instruct Photoshop not to save extra data in its images.
In the example James showed, he tried to reduce a 6k file that had already been optimized by professional PS/web designers. Doubt anyone could reduce that significantly without loss of resolution.


john mcwilliams
JM
James McNangle
Apr 25, 2006
tacit wrote:

That is because you have instructed Photoshop to save lots and lots of extra data, such as color profile information, thumbnails, previews, EXIF data, and so on, in your image.

If you wish to save an image for Web use, do not use the Save As command. Use the Save for Web command. Save for Web does not save this extra data.

Thank you for this information. It answers most of my questions. I used to be fairly familiar with file formats, but I had no idea that all this extra stuff could be could be hidden in a .jpg file. Is it all described anywhere?

Or, instruct Photoshop not to save extra data in its images.

Is this an option?

I resaved all the Images in one directory using the "Save for Web" option, and almost halved the size of the directory. However one particular .gif file, which I had found somewhere on the Web, grew in size, regardless of the quality setting. Even more puzzling, the original file shows no visible artefacts, yet the lowest quality .jpg file shows obvious artefacts, even though it is bigger.

This image is shown at http://www.corybas.com/Technical/Image_size.htm#Peynet

I tried saving all the Images as .gif, but most grew alarmingly in size. However this particular image only grew by 1KB, and was still smaller than any of the .jpg files.

Can anyone explain this?

James McNangle
JM
James McNangle
Apr 25, 2006
John McWilliams wrote:

In the example James showed, he tried to reduce a 6k file that had already been optimized by professional PS/web designers. Doubt anyone could reduce that significantly without loss of resolution.

I have not been trying to reduce the size of existing photos, but to explain why if I took an existing photo from the Web, and edited it in any way, it almost always became much larger. For my demonstration I simply resaved an existing photo without altering it so that the change in size was not confused by size changes due to editing.

James McNangle
2
2
Apr 25, 2006
"James McNangle" wrote in message

I resaved all the Images in one directory using the "Save for Web" option, and
almost halved the size of the directory. However one particular .gif file,
which I had found somewhere on the Web, grew in size, regardless of the quality
setting. Even more puzzling, the original file shows no visible artefacts, yet
the lowest quality .jpg file shows obvious artefacts, even though it is bigger.

This image is shown at
http://www.corybas.com/Technical/Image_size.htm#Peynet

Let’s step back a bit. First of all, the GIF is not really big. Don’t sweat it. The GIF is only four ‘colors’ (shades of grey) and won’t ever get smaller than 12 to 13K and retain quality. That’s tiny!

The JPEG was likely saved incorrectly somehow. Why not save it as GIF anyway? It will probably shrink to 8K.

The more often you change, save, and open a JPEG the more likely it is to diminish in quality.

GIF is good for things with fewer than 255 colors especially with monochrome line-art. JPEG is good for retaining colors. You images have no color. Use GIF.

== and a small side note – when you save from a smaller disc to a much larger one, images will almost always be a bit bigger because of a thing called "cluster factor". Don’t worry about it.
2
2
Apr 25, 2006
Two more things: Of course the lowest quality JPEG will look wors: it is low quality – it throws away and mungs more detail.

More important – when you use Save For Web, look to the right of the screen and you will see the number of colors in the image. For your particular monochrome line art all you need is four (4) colors. Two colors will destroy the subtle boundaries – not good. If your colors setting is not AUTO, then set it so, or change the number of colors to 4. If it looks bad, then try 8.

GIF is generally sharper than mid-to-low quality JPEG when the GIF image has a range of colors (or greys) that fit into its narrow scale of colors.
I
iehsmith
Apr 25, 2006
On 4/25/06 8:10 AM, 2 commented:

GIF is generally sharper than mid-to-low quality JPEG when the GIF image has a range of colors (or greys) that fit into its narrow scale of colors.

I’d just like to reinforce what you intimated, for these lineart images select grayscale for your colors, and there is no need for dithering an dithreing adds a bit to K. Choosing GIF format is best for these particular images because it handle areas of solid color so much better than JPEG, whereas JPEG is normally better for photo or art with a lot of colors and blends. It really is a matter of experimenting and practice. There is no one set way to save all images for the web. You just need to learn what does what and decide how much quality you want to trade off for optimization. Use your eyes, don’t just depend on numbers, unless you don’t care what they look like;)

If you need to scale a GIF image remember to change your Image>Mode to RGB or Grayscale first (replacing Indexed). This allows the bits to be resampled properly. Then change your image size, unsharp if needed, then re-Save for Web. That GIFs are indexed color is one reason they are sharper and more define. For this same reason, you cannot force-resize them by html for thumbnails and such as they will generally look like garbage. I like that though. <rant>I hate forced sizing for thumbnails; the things take just as long to load because they still contain the same size information. Lazy, bad web people; and lazy to use JPEG just because you can force the size!</rant>

Others will have to tell you the technical reasons the images act in particular ways.
T
Tacit
Apr 26, 2006
In article ,
James McNangle wrote:

Thank you for this information. It answers most of my questions. I used to be
fairly familiar with file formats, but I had no idea that all this extra stuff
could be could be hidden in a .jpg file. Is it all described anywhere?

It’s described on Adobe’s Web site. The metadata Photoshop saves in its files includes EXIF data, thumbnail previews, custom icons, color profile information, and paths,

Or, instruct Photoshop not to save extra data in its images.

Is this an option?

Yes. Preferences->File Handling, and Color Settings (for color profile information).

I resaved all the Images in one directory using the "Save for Web" option, and
almost halved the size of the directory. However one particular .gif file, which I had found somewhere on the Web, grew in size, regardless of the quality
setting. Even more puzzling, the original file shows no visible artefacts, yet
the lowest quality .jpg file shows obvious artefacts, even though it is bigger.

GIF and JPEG compress and store image information differently. If you take a GIF and then re-save it as a JPEG, the file size will change. If it started out as a GIF, re-save it as a GIF.


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Nanohazard, Geek shirts, and more: http://www.villaintees.com

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