Hi All,
Yes, as Sven said, we should profile the presentation at first. It is the
most right way to improve the performance.
And I also agree that the original image should better be kept.
But let's think about this thing:
OO is not a professional software of image processing. What we should do is
to make the customers thinking the images quality is well when printing,
presenting and showing etc. They aren't interesting of whether the image is
scaled or what size it should be, are they? In which condition should we must
use the original pixels to do something?
Let's think about the necessity and feasibility of descaling image which
could be saved in document.
I have tested some images in my computer, I found that the presenting speed
is not depended on the size of image file but on the resolution of it. For
example, I saved an original JPEG image(2304*1728, 371KB) to different formats,
such as BMP, TIFF, PNG. The sizes of them are 15.1MB,18.6MB and 2.42MB
accordingly. It spends almost same time to present them. If the image has
1152*864 pixles with 10MB, the time is 75% of the original. The less
resolution, the faster drawing.
So I think decreasing the resolution can increase the speed of presentation.
And let's see how Microsoft PowerPoint do it. I insert the above JPEG image
with the original rect set by MS and saved as 1.ppt. 2.ppt has the same image
with the 1/4 rect of 1.ppt. Decompress these files to packages with XML files,
we can see that in the 1.ppt the saved JPEG image has the original size and
resolution(2304*1728, 371KB) but in 2.ppt, which has 1100*825 resolution and
169KB size while keeping JPEG formation. If the 2.ppt is copyed to another
computer, the user can not get the original image again. Does this example
prove that MS also don't keep the original files? I think so.
So, I think descaling the image not only can improve presenting performance
but is a feasible way.
Basing on this, our test-department colleagues tested the displaying impact
of downscaled image in printing, presenting, projecting and showing in PC and
MID(Mobile Internet Device). What we used devices are HP LaserJet 1020 with
FastRes 1200(higher than 600 dpi), SANYO PLC-XW6680CA projector and SONY
VPL-CX6 projector, and the MID has 1GHz CPU with 512MB DDR2 memory and 7" LCD
with 800*600 resolution. We set the threshold is 1000 pixel for column and row.
The original image is scaled to that whose column or row has less than 1000
pixels, such as 2304*1728 to 1152* 864. We tested several images with different
formations. Compared with no-downscaled image, the impact has not the obvious
difference and the speed is increased especially for MID.
In conclusion, I think descaling the resolution of image is an acceptable
way to improve performance with no-decreased impact and we need not hold the
original image in our files.
If you agree with it, I think the next step is to find how and where to
descale the high-res image. Maybe we can provide an option to let the user
deciding whether saving the original size or not when he saving a file.
2009-01-12
sunyinan
发件人： Sven Jacobi
发送时间： 2008-11-27 01:23:31
收件人： [email protected]
抄送：
主题： Re: [graphics-dev] [Impress] Information about improvingperformance
Christian Lippka - Sun Microsystems GmbH - Hamburg wrote:
> Hi All,
>
> I personally do not like to scale down images that the user wants to
> embed in the document. I have not
> checked it yet but I believe if Microsoft does it they only do it as a
> cache for non embedded images.
> I'm pretty sure that we will get flames from users if they print their
> documents and the images have
> data loss.
> On the other hand, I think that Sven Jacoby already implemented
> something that loads pictures in a
> smaller size. That was needed to optimize rendering of the preview
> images for slides. Maybe this can
> also be used for speeding up the presentation? I cc'ed him so he
> hopefully will comment on this.
>
> Regards,
> Christian
>
We are able to load jpeg graphics faster by leaving out scanlines and we
also take
care of the png progressive mode when loading preview graphics but this
mechanism
is no solution. Leaving out scanlines is no proper downscale method and
will result
in a bad image quality.
I think before starting a discussion on how to improve the performance,
the presentation
should be profiled so that we have some numbers we can deal with.
Regards,
Sven
> Thorsten Behrens wrote:
>> On Tue, Nov 25, 2008 at 02:01:02PM +0800, sunyinan wrote:
>>
>>> As for a fast scaler, I think there must be two for-loops to
>>> extract the pixels from lines and columns. So from this, it is hard
>>> to be faster.
>>>
>>>
>> Hi sunyinan,
>>
>> well, the referenced bmpfast.cxx does speed things up, e.g. by
>> taking one scanline at a time. But you won't get orders of magnitude
>> with this, that's true.
>>
>>
>>> So I think scaling image when decoding is an acceptable way even
>>> it slows down the inserting speed. What do you think about it?
>>>
>> I don't like that, at least not if it's done unconditionally. Better
>> make that an option, and better still, do both - keep the original
>> file, and have a low-res "preview" bitmap along with it, maybe even
>> stored on disk.
>>
>>
>>> Another question is that GDI+ is used to "slide show" the presentatio
>>> while GDI to the presentation. As we all know, GDI+ is slower than GDI
>>> ( if DrawImage method is repleased by bitblt, the speed is more fast
>>> than now). So, why don't we also use GDI for "Slide show"?
>>>
>>>
>> Because GDI doesn't do antialiasing. But feel free to replace the
>> DrawImage call with a GDI method, the difference in quality is
>> usually not too big for pictures.
>>
> Well we already have an issue with some votes that Impress does not
> scale images as
> nice as PowerPoint does, so I would not count on this.
>
> Regards,
> Christian
>
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