If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Rate Thread | Display Modes |
#1
|
|||
|
|||
Reducing picture size with same quality.
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter |
Ads |
#2
|
|||
|
|||
Reducing picture size with same quality.
On Fri, 23 Mar 2012 14:46:51 +1100, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter, I would be asking this question in one of the Photoshop newsgroups, of which I see about 10 on my news server. |
#3
|
|||
|
|||
Reducing picture size with same quality.
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter There are a couple ways to shrink picture size. 1) Resolution change. You can use "scale image" in your image editor, and change the locked together "X resolution" and "Y resolution" settings from say 1200 DPI to 600 DPI. That cuts the number of pixels by a factor of 4. 2) You can use a lossless compression format. I think GIF is lossless, but it only supports pictures with 256 colors. There are other examples here of lossless methods. You might get a factor of 3 using a lossless method. Using (1) and (2), we can get close to a factor of 12. http://en.wikipedia.org/wiki/Image_compression 3) Once you move to a lossy compression method, then you're in control of the picture quality versus size tradeoff. http://en.wikipedia.org/wiki/Jpeg If you look at the "Jpeg tombstone" image further down that page, and look at Q=10, you get a compression of 46:1 . Which is a significant improvement. There are other methods of compression. The JPEG article mentions the algorithm isn't applied all that intelligently, and there are some options for further improvement. But then, the person receiving the picture, might not have a decoder for it. Another form of compression, involves fractals. http://en.wikipedia.org/wiki/Fractal_compression That article says fractal compression starts to win, at compression ratios higher than 50:1. And that's why I picked the Q=10 picture in particular, from the JPEG article. If the picture quality at Q=10 is good enough, you probably can't do much better with the fractal method. But if the quality is unacceptable, then a fractal method taking a long time to compress, may achieve a more pleasing result. Most good lossy compression methods (100:1 compression), will tend to have a weakness for certain kinds of content. They may do better with "natural images", than with artificially generated images (like a cartoon with solid colors). A cartoon sees excellent compression with GIF, probably higher than the factor of three that I quoted above. The best way to learn about this stuff, is to play with it. Paul |
#4
|
|||
|
|||
Reducing picture size with same quality.
On 23/03/2012 2:46 PM, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter http://answers.microsoft.com/en-us/w...9-ad9acd370b9b |
#5
|
|||
|
|||
Reducing picture size with same quality.
On 03/22/12 23:46, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter Because, when you transfer one gallon of beer, into an one pint glass, some of the beer will spill out. And that's against the Law in most Countries, (spilling beer, that's it)..... |
#6
|
|||
|
|||
Reducing picture size with same quality.
In message , Peter Jason
writes: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter My first reaction was to say they can't, but then I got to wondering what _method_ you are using in Photoshop (and, for that matter, the camera) to achieve smaller sizes. If you're reducing the image size in pixels, you obviously will lose definition. If you're reducing it by image compression, you won't lose definition, on the whole - you'll just risk getting artefacts visible in some places. If the "smaller" pictures your camera takes have quality/definition that's "very good", why do you take the larger ones at all (i. e. why not leave the camera set to "smaller")? [I'm curious to know whether it's a pixel-size or a "quality" setting thing in the camera. -- J. P. Gilliver. UMRA: 1960/1985 MB++G.5AL-IS-P--Ch++(p)Ar@T0H+Sh0!:`)DNAf ....Every morning is the dawn of a new error... |
#7
|
|||
|
|||
Reducing picture size with same quality.
On 3/22/12 9:46 PM, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter One question no one asked, what makes you say you lose definition? -- Ken Mac OS X 10.6.8 Firefox 10.0.2 Thunderbird 10.0.2 LibreOffice 3.5.0 rc3 |
#8
|
|||
|
|||
Reducing picture size with same quality.
On 22/03/2012 11:46 PM, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Peter Reducing image size (eg from 4000x3000 pixels to 1200x800 pixels) will "lose definition" as you cal it. There is no way around that. Reason: a detail that was shown with a 6x6 pixel square in the original image will now be shown by a 2x2 pixel square in the reduced image. You can use a a"lossless compression" algorithm, but your camera has already done that. The original image it took was a bitmap. The built in software converted that to the *.jpg image that you copied to your computer. Bottom line: unless you have good reasons to do so, do not make image files smaller. And if you must do so, always work ona copy, never on the original image. FWIW, I have a "working copies" folder to ensure that I don't mess with originals by mistake. Takes an extra step to copy the image, but worth it. HTH, Wolf K. |
#9
|
|||
|
|||
Reducing picture size with same quality.
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. -- Crash English is not my native tongue; I'm an American. |
#10
|
|||
|
|||
Reducing picture size with same quality.
On Fri, 23 Mar 2012 13:43:22 -0400, "Dave \"Crash\" Dummy"
wrote: Peter Jason wrote: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. No smiley? :-) -- Char Jackson |
#11
|
|||
|
|||
Reducing picture size with same quality.
On 23/03/2012 1:43 PM, Dave "Crash" Dummy wrote:
Peter Jason wrote: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. Won't work if by "reduce the image" you mean "change pixel dimensions." HTH Wolf K. |
#12
|
|||
|
|||
Reducing picture size with same quality.
Wolf K wrote:
On 23/03/2012 1:43 PM, Dave "Crash" Dummy wrote: Peter Jason wrote: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. Won't work if by "reduce the image" you mean "change pixel dimensions." Depends on what you mean by "won't work." Any reduction is going to lose detail because there are fewer pixels, but I have found that I get better quality when I scale down a lossless format than I do when I scale down a lossy one. -- Crash What happens online, stays online. |
#13
|
|||
|
|||
Reducing picture size with same quality.
Dave "Crash" Dummy wrote:
Peter Jason wrote: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. Doing that might make sense if the JPG was Q=95 and 4MB in size, and dropping to Q=10 would provide enough extra compression to shrink the file (and degrade the quality of the image). The question would be, whether PNG has a compression option, and once the JPG is decompressed, the PNG compression is better than the JPG compression (at whatever Q setting was used). http://en.wikipedia.org/wiki/Portabl...cs#Compression "Comparison to JPEG JPEG uses a lossy encoding method specifically designed for photographic image data, which is typically dominated by soft, low-contrast transitions, and an amount of noise or similar irregular structures. Using PNG instead of a high-quality JPEG for such images would result in a large increase in filesize with negligible gain in quality. By contrast, when storing images that contain text, line art, or graphics – images with sharp transitions and large areas of solid color – the PNG format can compress image data more than JPEG can, and without the noticeable visual artifacts which JPEG produces around high-contrast areas." So PNG is kinda like GIF, in that it likes "cartoon" type pictures, more than camera-captured pictures of natural scenes. For the most part, if it's a camera, sticking with JPEG and twiddling the Q knob, is a pretty good approach (in terms of being easy to understand, and easy for a recipient to deal with). HTH, Paul |
#14
|
|||
|
|||
Reducing picture size with same quality.
On 23/03/2012 3:14 PM, Dave "Crash" Dummy wrote:
Wolf K wrote: On 23/03/2012 1:43 PM, Dave "Crash" Dummy wrote: Peter Jason wrote: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. Won't work if by "reduce the image" you mean "change pixel dimensions." Depends on what you mean by "won't work." Any reduction is going to lose detail because there are fewer pixels, but I have found that I get better quality when I scale down a lossless format than I do when I scale down a lossy one. That's interesting, since AFAIK when the JPG is displayed or converted, it's first reconstituted as a bitmap. Thus the quality of the resulting PNG image would depend on the quality of the source JPG. AFAIK, the scaling algorithm works on the actual JPG/PNG/etc data. If, as you say, PNG reduced is better quality than JPG reduced, then there must be a subtle differences in the algorithms. Or else the data structures differ in what they conserve. Dash it all, now I'll have to do some research to find out what's going on! Anyhow, a JPG isn't necessarily lossy, it depends on the compression ratio. Cameras generally use the lossless ("high quality") compression ratio. Anyhow, all our cameras do so. Many simple image-viewers/processors use a lower quality ratio by default. You can find out if your does this by doing Save As on the original image with small name change, then comparing the file sizes. The programs I use offer setting the default compression ratio, so apart from the effects of the processing itself, there is no change/loss in quality. HTH Wolf K. |
#15
|
|||
|
|||
Reducing picture size with same quality.
On Fri, 23 Mar 2012 15:16:27 -0400, Paul wrote:
Dave "Crash" Dummy wrote: Peter Jason wrote: I have Win7 SP1. I take pictures of about 4 MB with a good quality camera. These are excellent, but I lose definition when these are reduced to about 500KB with software such as Photoshop. When I take small pictures with the camera the quality/definition is very good. I don't want to take two shots of everything just to be able to get small pictures for emailing. Why cant large quality pictures be reduced to smaller ones - with the same definition? Convert the large JPG image to a lossless format, like PNG, then reduce that image. Doing that might make sense if the JPG was Q=95 and 4MB in size, and dropping to Q=10 would provide enough extra compression to shrink the file (and degrade the quality of the image). The question would be, whether PNG has a compression option, and once the JPG is decompressed, the PNG compression is better than the JPG compression (at whatever Q setting was used). http://en.wikipedia.org/wiki/Portabl...cs#Compression "Comparison to JPEG JPEG uses a lossy encoding method specifically designed for photographic image data, which is typically dominated by soft, low-contrast transitions, and an amount of noise or similar irregular structures. Using PNG instead of a high-quality JPEG for such images would result in a large increase in filesize with negligible gain in quality. By contrast, when storing images that contain text, line art, or graphics – images with sharp transitions and large areas of solid color – the PNG format can compress image data more than JPEG can, and without the noticeable visual artifacts which JPEG produces around high-contrast areas." So PNG is kinda like GIF, in that it likes "cartoon" type pictures, more than camera-captured pictures of natural scenes. For the most part, if it's a camera, sticking with JPEG and twiddling the Q knob, is a pretty good approach (in terms of being easy to understand, and easy for a recipient to deal with). HTH, Paul Clearly this will take some research. I am impressed by the quality of many Internet images that are merely about 150KB in size and yet I cannot get mine anywhere near this quality, even with an expensive camera. Would taking in RAW help, and using this in some imaging software? I wonder how the Internet sites get their great detailed pictures. Peter |
Thread Tools | |
Display Modes | Rate This Thread |
|
|