I need to make from big png-file image less in width/height with maximum quality, despite of its size
I use imagemagick command like:
/usr/bin/convert -sample 1201x847 -density 600 "source_file.png" -quality 100 "dest_file.png"
I get png file but I would like to get image of better quality...
I set width/height of output file as -sample 1201x847
That is clear with -quality 100 - best quality
Not clear with density parameter
I read a doc:
-density width
-density widthxheight
Set the horizontal and vertical resolution of an image for rendering to devices.
This option specifies the image resolution to store while encoding a raster image or the canvas resolution while rendering (reading) vector formats such as Postscript, PDF, WMF, and SVG into a raster image. Image resolution provides the unit of measure to apply when rendering to an output device or raster image. The default unit of measure is in dots per inch (DPI). The -units option may be used to select dots per centimeter instead.
The default resolution is 72 dots per inch, which is equivalent to one point per pixel (Macintosh and Postscript standard). Computer screens are normally 72 or 96 dots per inch, while printers typically support 150, 300, 600, or 1200 dots per inch. To determine the resolution of your display, use a ruler to measure the width of your screen in inches, and divide by the number of horizontal pixels (1024 on a 1024x768 display).
If the file format supports it, this option may be used to update the stored image resolution. Note that Photoshop stores and obtains image resolution from a proprietary embedded profile. If this profile is not stripped from the image, then Photoshop will continue to treat the image using its former resolution, ignoring the image resolution specified in the standard file header.
The -density option sets an attribute and does not alter the underlying raster image. It may be used to adjust the rendered size for desktop publishing purposes by adjusting the scale applied to the pixels. To resize the image so that it is the same size at a different resolution, use the -resample option.
Did they mean params of monitor of client screen.width and screen.height ?
As it was written:
use a ruler to measure the width of your screen in inches, and divide by the number of horizontal pixels (1024 on a 1024x768 display
It was not actually very clear about these parameters and how to calc it.
Also googling I see using of parameters -sharpen, -trim, -resample - do they influence quality of resulting and if yes how to use them ?
About source png file I know only that it is result of fabrics js canvas using html2canvas function.
How to get image of better quality?
Thanks!
Related
I am using GIMP 2.10.24. I have some image and I need to change Print Size Width to 21mm and Height to 30mm.
I can do that with Set Image Print Resolution Dialog (Menu->Image->Print Size):
screenshot
But there is my question: how could I do that using script-fu or python-fu?
Print size, size in pixels, and print definition are completely related:
print size = size in pixels ÷ print definition
So to change the image print definition you use
In Python:
pdb.gimp_image_set_resolution(image, xresolution, yresolution)
In Script-fu:
(gimp-image-set-resolution image xresolution yresolution)
In both case the X/Y resolutions are in dots per inch.
However if you are using Gimp just for this creating a Gimp script is overkill (the learning curve is quite steep). If the image is in a common format (JPEG, PNG, TIFF) the print definition is part of the image metadata (JPEG header, or EXIF data) and can be changed directly without decoding/reencoding the image using CLI utilities. For instance with ExifTool:
exiftool ${your_image} -xResolution=321 -yResolution=321
I have a bunch of auto-scanned slides using a slide scanner (Hamamatsu), which I can export from the NDPview software at different magnifications. So far, I have been zooming in to where I get the best resolution of my region on interest and add a scale bar for 1mm (as 1000 um) using the native scale bar option in the NDP view software. I then export the "view" from NDPview to TIFF. This TIFF is then imported into ImageJ (Fiji) where I set the scale using the scale bar I drew. This has been working well, but with over 500 images to do it's a bit of a pain.
Since the TIFF imports to ImageJ with inchxinch dimensions, I figured I can go to Image -> Properties and just change the unit of length to um. To test this, I selected an area to measure. I then compared this to my old method... and the values are completely different. Any idea why? 1 is the old method, 2 is the new method.
I made certain to "remove scale" in the scale bar window between each test. The whole image dimensions are different too:
If the images are all the same magnification and resolution, then as long as you know a measured distance (in pixels) and the physical distance (in microns or mm), you can set it using Analyze > Set Scale...
To do this in a macro you can use
run("Set Scale...", "distance=255 known=1 pixel=1 unit=micron");
where 255 is the distance in pixels for your known unit (1 micron). This can be applied to all TIFFs in a folder if you wrap that line in a loop operating on all TIFFs and save each resulting image.
I have designed a lock icon in Sketch to add to a button in my application:
I exported it both in pdf and png (2x, 3x) to add to Xcode assets. Problem is when I run the app on iPhone (SE), heavy pixelation can be seen around the edges of the icon:
I've tried both pdf and png formats, but result stays the same. Am I missing any settings that need to be applied for image to look sharp on screen?
Bigger is not necessarily better for a UIButton's image. Try to export your icon in more or less the same size with which it will be used. (Note that this also frees up memory in comparison to a way bigger image).
To adapt to different screens' resolutions, you should provide up to three images (#1x, #2x, #3x). You should read this excellent Apple's documentation on Image Size and Resolution. It explains perfectly how big should the images you provide in Xcode be.
They also have a good explanation on which format you should use according to the purpose of the image.
EDIT:
You can also use vector ressources (.pdf files for instance) that will render perfectly for any resolution. You can read this article about how to implement it in your Xcode project (If you do so, please be careful in the attributes of the asset to check Preserve Vector Data and the Scales to Single Scale, otherwise it may not render well).
It will happen if image sizes are not correct
check the size of images. 1x,2x and 3x sizes are should be as followed
1x = 24x24 px
2x = 48x48 px
3x = 72x72 px
If images size are too big than ImageView then pixelate will happen
Hope this will help you
I have to write a CGPDFContext. This PDF contains just one image.
The image has 2100 x 3000 pixels.
Suppose I open this image on Photoshop and print it at 300 dpi. Photoshop will use 300 pixels to build every inch of printed material, so this image will have 7 x 10 inches.
This image has this size because of that.
Now I have to create a CGPDFContext. I read somewhere that this context has to be created in points and there is a mention that on a CGPDFContext one point = 1/72 inches, meaning that the context will have 72 dpi (?).
So, what size should I create this context to have maximum quality at 300 dpi.
Another question is this: supposing this context is created based on the 1/72 stuff, than 7 x 10 inches will represent 504 x 720 pt. If this is the size I have to create the context, what happens when I write the image to the context using this?
CGImageRef imageRef = image.CGImage; // this image is 2100x3000 pixels
// mediaBox = 0,0,504,720
CGContextRef pdfContext = CGPDFContextCreate(dataConsumer, &mediaBox, auxillaryInformation);
CGContextDrawImage(pdfContext, CGRectMake(0.0f, 0.0f, 504, 720), imageRef);
will the 2100x3000 pixels image be embedded on the context without losing pixels? I don't want the image to be reduced to 504x720
If your image is 2100*3000 pixels and you draw it on a PDF page that is 7*10 inches (504*720 points) then your image will be embedded at 300 dpi.
The image size will be kept at 2100*3000 pixels and it will not be downscaled at 504*720 pixels.
Both other answers are technically correct, but let me try to answer explicitly on both of your questions:
Now I have to create a CGPDFContext. I read somewhere that this
context has to be created in points and there is a mention that on a
CGPDFContext one point = 1/72 inches, meaning that the context will
have 72 dpi (?).
The parameter you have to pass is the location and size of the mediabox of the PDF you want to create. The mediabox is the canvas you have at your disposal to put stuff on.
PDF uses a space where 1 point equals 1/72 inch, but you shouldn't think of this as dpi in the traditional "image" way. This is simply a convention so that you know that specifying a mediabox with a size of 72 x 72 points will give you a PDF file that is 1 inch high and wide in the real world.
So, what size should I create this context to have maximum quality at
300 dpi.
Your code is correct :-)
The image you place on this context will always be inserted as full size (meaning, Apple will not throw away pixels behind your back). That means that the final resolution of your image is determined by the number of pixels of your image and the size of the rectangle (again in points) where you chose to put it on the page.
So you're fine in this simple example. However (at the risk of hurting your brain), keep in mind that PDF contexts - just as any other contexts - allow you to transform them. You could rotate or shear the current transformation matrix of your PDF context. In that case your image would still have all pixels, but it's effective resolution would be dependent on what evil thing you did to the transformation matrix.
The resolution is independent of the media size, in PDF. The media size is given in 1/72 inch, so 2100x3000 'units' (aka points) is a media size of 29.166x41.666 inches. PDF files do not have a resolution.
In general the content of a PDF is vector information and so is resolution independent. Bitmaps may be drawn in a PDF, and those do have a resolution, but its not 72 dpi. The resolution of the image depends on the number of image samples in each dimension, and the scale factor which is applied to put it on the medium.
Consider an image which is 300x300 image samples. If we place that onto a PDF which is 72x72 (ie 1 inch square), and scale it to fit exactly, then the image is, effectively, 300 dpi internally.
In PDF terms I can take the same image, make a PDF page which is 144x144 (2x2 inches), and scale the image to fit that. Now the image is 150 dpi. The image hasn't changed, but the scale factor has.
Now the final 'resolution' of any images in your PDF file, when rendered, will depend on the number of samples and scale factor (as above) and the resolution you render the PDF file at. Taking the 2 cases above, if I render at 300 dpi, the image won't change at all, but in the first case will map 1:1 the original image samples onto the final output pixels. The second image, however, will map each image sample into 4 pixels in the output (because its been scaled by 2 in each direction).
If you render your PDF file (2100x3100 points) in Photoshop #300 dpi then Photoshop will create a bitmap which is 8750x12500 pixels. It will still be 29.16x41.66 inches, at 300 dots per inch. If you render it at 600 dpi, then you will get 17500x25000 pixels, and so on.
It sounds like the context is created in the default PDF space of 1/72 inch, so you just need to use the media size from the PDF file, ie 2100x3100.
My netbook has a monitor with 10.1 inch length and 1024*600 solution. I think 1pt is about 1/72inch - is the following computation right?
Since the resolution is 1024*600, the
diagonal has about 1186.83 pixels,
thus 1 inch is about 1186.83/10.1 =
117.51 pixels, and thus 1pt is about 117.51/72 = 1.63 pixels, or 1 pixel is about 0.6127 pt.
Using this relationship, I've inserted an image into a LaTeX document, converting pixels to pt, and take the result as a parameter to includegraphics, but the figure in the resulting document is rather blurred.
Is the computation correct? if
not, how or
where am I wrong?
How can I insert an image into a LaTeX document
with precisely the same dimensions as the
original?
Updated:
I'm using pdflatex to compile the document and the image is a png file, and the reason why I do such a stupid computation is that with no width parameter set, the image shown in the document is larger than the actual size, and I can't work out why.
LaTeX is for creating paper documents. The units it uses refer to distance on the paper output, not on the screen. So if you ask for a distance of 72pts in LaTeX, you'll get 1 inch on your printout, but the distance you get on your screen depends on the zoom-level of your pdf or ps reader, which probably doesn't know how big your screen is.
If you simply want to get the raster grid of your image to fit to the screen grid, I'd say the best thing to do is get a higher-quality graphic if you can.
(PS there's a TeX stack exchange site where you could ask your question too...)
I don't know if it will make any difference, but TeX actually uses 72.27 points to the inch (as it predates PostScript, which set the standard 72 points to the inch).